Alternative Underground Propane Tank Materials, Final … Alternative...... for pressure vessels....

Alternative Underground Propane Tank Materials, Phase II

Final Report By

Joan Muellerleile, Barry Hindin, and Rodney Osborne Battelle Memorial Institute

Chad Cederberg, Brian Yeggy, and Norman Newhouse Lincoln Composites

Prepared for

Propane Education & Research Council 1140 Connecticut Ave. NW, Suite 1075 Washington, DC 20036 Dockets 12069 and 12096 September 2009

Disclaimer Battelle does not engage in research for advertising, sales promotion, or endorsement of our clients' interests including raising investment capital or recommending investment decisions, or other publicity purposes, or for any use in litigation. Battelle endeavors at all times to produce work of the highest quality, consistent with our contract commitments. However, because of the research or experimental nature of this work, the client undertakes the sole responsibility for the consequences of any use or misuse of, or inability to use, any information, apparatus, process, or result obtained from Battelle, and Battelle, its employees, officers, or Directors have no legal liability for the accuracy, adequacy, or efficacy thereof.

Alternative Underground Propane iii September 2009 Tank Materials, Phase II—Final Report Battelle and Lincoln Composites

EXECUTIVE SUMMARY

Currently in the U.S., all underground propane tanks are made of steel and conform to the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code. The cost of steel is increasing and additional costs are incurred for corrosion protection if the tank is buried. The result is a significant rise in the overall cost of underground propane tanks. Composite materials are used for a variety of structural components because of their lighter weight and higher resistance to chemical attack, including corrosion. Composite materials are used for low-pressure liquid storage tanks and, increasingly, for pressure vessels. Several manufacturers worldwide produce high-pressure composite vessels for compressed gas use, such as the storage of compressed natural gas and hydrogen. At least four international companies and one U.S. company are producing and marketing composite liquefied petroleum gas (LPG) or propane cylinders. Two manufacturers have U.S. Department of Transportation (DOT) approval to market cylinders for sale and use in the U.S. In this context, the Propane Education & Research Council (PERC) launched a study to determine the feasibility of developing propane storage tanks from materials other than steel. In the initial Phase I study (PERC Docket 11728, Muellerleile, et al., 2005), Battelle determined that alternative materials were sufficiently plausible to warrant a more detailed design study involving a tank manufacturer. For this Phase II effort, Battelle partnered with Lincoln Composites, a manufacturer of high pressure composite cylinders, based in Lincoln, NE. This report is a summary of the Phase II detailed design continuation of the initial Phase I preliminary design work. In this regard, the current report presents the design methodology and design details for a 500-gallon (1900 liter) composite propane tank for underground service. This design is based upon previous experience with the manufacturing of composite pressure vessels for high-pressure use, underground petroleum storage tanks. The design process considered tank static pressure and soil loading. As a result of this Phase II study, the current preferred design for a composite propane tank is composite tank design and tooling developed for a 41-inch diameter pressure vessel. The composite propane tank consists of a high-density polyethylene (HDPE) copolymer liner fully wrapped with AdvantexTM glass fiber-reinforced epoxy. A boss, made from aluminum alloy 6061-T651X, is in each head of the composite propane tank. The boss at the service end provides a single penetration into the tank for vapor service, filling, liquid level gauging, and the safety relief valve flow path. The boss at the non-service end serves a tail-stock-type function during the fiber winding process as well as providing structural support at confluence point of the fibers over the head. The current composite propane tank designs include nominal 250-, 500-, and 1000-gallon tanks. As a result of the ability to change length with minimal impact on tooling, all three designs are simply length variations on a single composite layup. The baseline composite propane tank is designed for 250 psi with a 5:1 stress ratio and 20 percent margin for internal pressure loads. However, this requirement does not drive the thickness of the design. Rather, the design thickness is driven by external underground loading requirements per AWWA M45 Fiberglass Pipe Design Manual (AWWA, 2005). This thickness results in a stress ratio from

Alternative Underground Propane iv September 2009 Tank Materials, Phase II—Final Report Battelle and Lincoln Composites

internal pressure near 7.4:1. In addition to the tank itself, the development effort includes a riser design. The proposed riser extends to the ground surface from one of the composite propane tank end openings. This riser includes a vertical pipe housing a tube to connect the vapor space of the vessel and riser, and space for a fluid level sensing system. The riser pipe is topped with a combination valve typically used for underground service applications. A gusset system is included for stabilizing the riser to the vessel during transport. Figures ES-1 and ES-2 show engineering renderings of the current composite propane tank design. In order to help strengthen the case in support of composite use as an alternative to steel for underground propane tanks, a materials compatibility evaluation was performed using literature data to assess the compatibility of the proposed composite materials with components found in commercial propane. There were no laboratory tests performed on this project. We believe that there are no issues of concern at this point regarding chemical compatibility. The details of the materials compatibility study are detailed in a subsequent section of this report. It is of importance to note that the appurtenances in the alternative materials composite propane tank are metallic and, therefore, subject to potential corrosive deterioration. The appurtenance corrosion issue is also addressed in a subsequent section of this report, and it is believed to be manageable in most underground environments.

Figure ES-1. Side View Rendering of Preferred Underground Composite Propane Tank

Alternative Underground Propane v September 2009 Tank Materials, Phase II—Final Report Battelle and Lincoln Composites

Figure ES-2. Vapor Space Connection

Engineering estimates for the marketer’s price for different sizes of underground propane tanks based on variants of this basic conceptual design are shown in Table ES-1. Also shown here are estimated tank weights.

Table ES-1. Comparison of Steel, Phase II, and Potential Optimized Composite Tank Costs of Various Volumes

Attribute Steel

Composite Phase II Design

Current Design Potential Optimized Costs

(Estimated)

Volume (g=gallons, l=liters)

250 g 950 l

500 g 1900 l

1000 g 3800 l

250 g 950 l

500 g 1900 l

1000 g 3800 l

250 g 950 l

500 g 1900 l

1000 g 3800 l

Weight (lb) 480 930 1750 436 733 1325 420 700 1250

Dimensions (inches)

32 (d) 86 (l)

38 (d) 120 (l)

41 (d) 192 (l)

41 (d) 61 (l)

41 (d) 110 (l)

41 (d) 208 (l)

41 (d) 61 (l)

41 (d) 110 (l)

41 (d) 208 (l)

Marketer Cost, US$*

$1230 $1716 $2810 $3676 $4406 $5863 $1700 $2400 $3600

* F.O.B. factory, including combination valve.

Alternative Underground Propane vi September 2009 Tank Materials, Phase II—Final Report Battelle and Lincoln Composites

These estimated marketer’s prices are based on current equipment and tooling and include an estimate for hardware for fluid level monitoring. Hardware for fluid-level is an estimate only because at present there is no code-approved commercially available means for fluid level monitoring in a buried tank. Various approaches have been identified and assessed, but still required development for a field-ready practical system. Through increased production volume, specialized tooling, and continued development effort, it should be possible to reduce the gap between these projected prices and those realized once serial production is reached. It is important to note that for the Phase I preliminary design, a number of issues regarding manufacture and cost were not examined in detail for that initial work. As a consequence, there are additional cost and weight issues regarding manufacture and design that came about with the more detailed Phase II design. The last columns in Table ES-1 show projected prices based on aggressive cost reductions achieved through these development efforts. However, with oil-based polymers (resin and liner) comprising approximately 60 percent of the material cost of the composite tank, it is likely that the long-term costs are likely to track future oil prices. While the composite tank does have desirable features above steel tanks, the possibility of long-term price instabilities may offset these features.

Alternative Underground Propane vii September 2009 Tank Materials, Phase II—Final Report Battelle and Lincoln Composites

Table of Contents Page

Executive Summary ....................................................................................................................... iii

Introduction ......................................................................................................................................1 Background ................................................................................................................................1 Project Objectives ......................................................................................................................1

Summary of Previous Phase I Work ................................................................................................3

Phase II Engineering Design and Analysis ......................................................................................5 Customer Requirements .............................................................................................................5 Regulatory Requirements ...........................................................................................................6 LPG Tank Design Development and Selection .........................................................................6 Tank Construction ......................................................................................................................6 HDPE Copolymer Liner ............................................................................................................8 Composite Shell .........................................................................................................................9 Hardware ..................................................................................................................................10

Filling and Vapor/Liquid Service Interface .................................................................11 Riser Construction .......................................................................................................11 Vapor Space Connection..............................................................................................12 Liquid Draw .................................................................................................................13 Gusset ...........................................................................................................................13 Fluid-Level Sensing .....................................................................................................13 Pricing ..........................................................................................................................15 Cost Estimates ..............................................................................................................15 Opportunities for Price Reduction ...............................................................................16

Detailed Design Conclusions ...................................................................................................18

Composite Materials Compatibility ...............................................................................................20

Corrosion of Appurtenances ..........................................................................................................23 Underground Environments – Corrosion Processes in Soils ...................................................24

Soil Classifications .......................................................................................................24 Soil Parameters ............................................................................................................25 Soil Conductivity .........................................................................................................26 Temperature Considerations ........................................................................................26 Oxygen Concentration .................................................................................................27 Role of Galvanic Corrosion .........................................................................................27 Role of Crevice Corrosion ...........................................................................................28 Role of Microbiologically Influenced Corrosion (MIC) .............................................28 Estimate of Corrosion Rates of Appurtenances in Soils ..............................................28 Estimate of Atmospheric Corrosion of Appurtenances Under the Dome ....................30 Aluminum ....................................................................................................................31 Copper and Brass .........................................................................................................31 Ductile Iron ..................................................................................................................32 Stainless Steel ..............................................................................................................32

Alternative Underground Propane viii September 2009 Tank Materials, Phase II—Final Report Battelle and Lincoln Composites

Steel..............................................................................................................................32 Zinc ..............................................................................................................................33

Summary of Corrosion Data and Analysis ..............................................................................33

Conclusions and Recommendation for Future Work.....................................................................36

References ......................................................................................................................................38 Appendix A. Product Design and Analysis Report: Underground LPG Storage Tank

Alternative Underground Propane ix September 2009 Tank Materials, Phase II—Final Report Battelle and Lincoln Composites

Table of Contents (Continued) Page

List of Tables

Table ES-1. Comparison of Steel, Phase II, and Potential Optimized Composite Tank Costs of Various Volumes .......................................................................................................... v

Table 1. Estimated Underground Tank Costs – Steel and Phase I Composite Design ................... 3 Table 2. Service Conditions and Nominal Tank Properties ............................................................ 5 Table 3. Typical Properties for the High-Density Polyethylene Copolymer .................................. 8 Table 4. Properties of 6060-T651X Aluminum Alloy .................................................................... 9 Table 5. Composite Shell Layer Architecture ................................................................................. 9 Table 6. Properties of Owens-Corning 158B Type 30 Glass Roving ........................................... 10 Table 7. Properties of the Lincoln-Formulated Neat Epoxy Resins ............................................ 10 Table 8. Fluid Sensing Level Options .......................................................................................... 14 Table 9. Comparison of Initial Estimated and Potential Costs After Reductions (U.S. Dollars) . 17 Table 10. Required and Observed Chemical Compositions of Commercial Propane ................. 21 Table 11. Chemical Compatibility Data for Phase II Tank Design Components ........................ 22 Table 12. List of Alloys Used in Appurtenances .......................................................................... 23 Table 13. Nominal Alloy Composition of Alloys (Compositional data, accessed May, 2007) ... 24 Table 14. Types of Soils Listed in Order of Water Retention Capacity (Corrosion Doctors, 2007)

..................................................................................................................................... 25 Table 15. Corrosivity Ratings Based Upon Soil Resistivity ......................................................... 25 Table 16. Numerical Corrosivity Scale (ANSI, 1999) ................................................................. 26 Table 17. Corrosion Rates of Zinc in Various U.S. Soils (ASM, 2005c) ..................................... 30 Table 18. Summary of Expected Corrosion Performance for Appurtenances in Soil and Under

Dome ........................................................................................................................... 34

List of Figures Figure ES-1. Side View Rendering of Preferred Underground Composite Propane Tank .......... iv Figure ES-2. Vapor Space Connection ........................................................................................... v Figure 1. Tank Construction Section View. ................................................................................... 7 Figure 2. LPG Cluster Valve. ...................................................................................................... 11 Figure 3. Side View Rendering of Preferred Underground Composite Propane Tank ............... 12 Figure 4. Proposed Tank System Vapor Space Connection and Side View ................................ 13 Figure 5. Cost Estimates for the 250-, 500-, and 1000-Gallon Underground Composite Propane

Tanks ........................................................................................................................... 15 Figure 6. United States Carbon Steel Prices, January 1997 to September 2009 .......................... 17 Figure 7. United States Carbon Polyethylene Resin Prices, October 2003 to September 2009 ... 18 Figure 8. Depth of Atmospheric Corrosion Attack on Aluminum Alloys 1100 (ASM, 2005a) .. 31 Figure 9. Typical Thickness Loss for Brass Alloys in Marine Atmospheres as a Function of Time

(ASM, 2005b) ............................................................................................................. 32 Figure 10. Corrosion Rates of Zinc Exposed to Different Atmospheric Environments

(ASM, 2005c) ............................................................................................................. 33

Alternative Underground Propane 1 September 2009 Tank Materials, Phase II—Final Report Battelle and Lincoln Composites

INTRODUCTION

Background

Steel pressure tanks and cylinders have been used for decades for propane storage and transportation. Above-ground storage tanks range from one hundred to tens of thousands of gallons. In the past several years, there has been increasing interest in burying tanks at customer sites, both residential and commercial. While underground tanks may have safety advantages, such as removing the tank from traffic areas, the main reason for burying propane tanks is for aesthetics, as a buried tank is out of sight, except for the access lid. Unlike the environmental issues associated with the underground storage of other fuels such as gasoline and fuel oil, the environmentally nontoxic nature of propane eliminates concerns regarding potential soil and water contamination (Sympson, 2005). Without proper corrosion protection, however, underground steel tanks are susceptible to corrosion and potential problems stemming from corrosion issues, such as a propane leak at a site in the tank wall that has corroded through (May, 2005; Nicholson II, 2005-2006; Eastern Propane, 2004; NPGA, 1991; NPGA, 1994). For additional details regarding general corrosion and corrosion protection of steel underground propane tanks, the reader is referred to the Phase I report for this project (PERC Docket #11728, Muellerleile, et al., 2005). The corrosion assessment reported in this present Phase II report, described below, considers the corrosion of appurtenances without the presence of general cathodic protection associated with standard underground steel propane tanks. Steel costs have dramatically increased in response to surging worldwide demand. Additionally, the costs involved with underground installation, cathodic protection, and monitoring result in the price of procuring and installing underground steel tanks to raise even higher (Sympson, 2005; Ryman and Ryman, 2005). In the past five years, steel prices increased sixfold, from just over $200 per ton in 2001 to over $1200 per ton in the summer of 2008, before falling back to $800 per ton at the end of 2008 (MEPS, 2009). Worldwide demand, especially in rapidly developing countries such as China, is also leading to shortages and increasingly stiff competition from European and Asian manufacturers, which are also driving steel prices higher (Ostroff, 2006; Rey, 2004a). Composites can offer a number of significant advantages over standard steel for cylinder and tank applications. Composite resistance to corrosion, especially for underground applications, is particularly attractive, as it eliminates the need for cathodic protection and monitoring of the tank. Its lighter weight also provides ease of handling for transport, installation, and removal compared to its steel counterparts (Rey, 2004b).

Project Objectives

Based upon these advantages of composites, and in response to continuing skyrocketing steel prices, the Propane Education & Research Council (PERC) continues to investigate alternative materials for underground propane tanks. To that end, the purpose of the present Phase II work


is to develop a detailed design for an underground composite propane tank starting from the previous Phase I preliminary design. An additional objective of the present Phase II work is to work with a composite pressure vessel manufacturer to develop a more fully detailed underground composite propane tank design, including addressing issues such as manufacturing costs and considerations that were not considered in detail for the Phase I preliminary design.


SUMMARY OF PREVIOUS PHASE I WORK

Before discussing the Phase II results, the previous Phase I preliminary design work will first be summarized for reference. Phase I of this project developed preliminary designs for composite propane tanks for underground service. The designs were based on previous experiences with underground petroleum storage tanks, considering tank design pressure, cyclic pressures due to temperature and filling, and soil loading. This feasibility design approach for underground composite propane tanks for residential use was based upon a combination of design codes: the American Society of Mechanical Engineers (ASME) Section X (Fiber-Reinforced Plastic Pressure Vessels) for the primary pressure vessel design, and the American Water Works Association (AWWA) Manual of Water Supply Practices M45 (Fiberglass Pipe Design) to account for the buried installation of the tank (ASME, 2004; AWWA, 2005). The Phase I preliminary design assumed a filament-wound tank using fiberglass and a good quality isophthalic resin for adequate performance in order to help minimize the cost of the tank. The approximate dimensions and marketers’ costs for 250-gallon and 1000-gallon composite tanks, based upon this feasibility design, are shown in Table 1. For comparison, estimated steel tank dimensions and marketers’ costs (from the 2005 report) are also shown in Table 1.

Table 1. Estimated Underground Tank Costs – Steel and Phase I Composite Design

Steel 250-gallon

Composite 250-gallon

Steel 1000-gallon

Composite 1000-gallon

Weight 484 lbs 260 lbs 1741 lbs 970 lbs

Total length 5 feet 5 feet 13 feet 13 feet

Diameter 32 inches 32 inches 41 inches 41 inches

Thickness 0.20 inch 0.42 inch 0.25 inch 0.51 inch

Cost* (F.O.B. plant site)

$800 (tank) + $ 75 (1 anode) $875

$1000 (appurtenances in head) $1125 (appurtenances in side wall)

$2075 (tank) + $ 150 (2 anodes) $2225

$2400 (appurtenances in head) $2550 (appurtenances in side wall)

* 2008 Dollars

Note that the costs for the steel tank in the above table do not include any cathodic protection monitoring costs over the service life of the tank, which are estimated to be on the order of $550. If these costs for periodic inspections are included, the total life-cycle cost of the composite tank may compare favorably to the steel tank. Thus, this Phase I preliminary cost analysis showed


that such alternative material underground tanks are potentially competitive with steel construction from a life cycle cost standpoint. The ASME design code for Fiber-Reinforced Plastic Pressure Vessels (ASME Boiler & Pressure Vessel Code, Section X) has more restrictive constraints for vessels that have both external and internal loads, such as when an empty tank is first buried and then filled. While the Section X constraint is intended for extensive load reversals, a propane tank will typically experience one load reversal during the initial burial followed by filling. The relaxation of this restriction could reduce the design margin, and therefore the manufacturing costs, of the composite tank for underground propane use. The standard National Fire Protection Agency (NFPA) Liquefied Petroleum Gas Code (NFPA 58, NPFA, 2008) governs the installation of propane systems. Section 5.2.1.1 (LP-Gas Equipment and Appliances, Containers, General) requires that containers be designed in accordance with the regulations of the ASME Boiler and Pressure Vessel Code, Section VIII, “Rules for the Construction of Unfired Pressure Vessels.” Section VIII allows metallic materials only. As mentioned above, pressure vessels fabricated from composite materials are addressed in Section X. Therefore, NFPA 58 would have to be modified to allow Section X-designed (composite) vessels in addition to Section VIII-designed (metallic) vessels.


PHASE II ENGINEERING DESIGN AND ANALYSIS

Starting with PERC’s requirements and Battelle’s Phase I preliminary concept design, Lincoln Composites, Inc., a manufacturer of high-pressure composite pressure vessels located in Lincoln, NE, revised and refined various composite propane tank design options, resulting in the preferred composite propane tank design described below. Following is a summary of the initial design requirements, with service conditions and nominal tank properties listed in Table 2. The full design report is provided in the Appendix.

Table 2. Service Conditions and Nominal Tank Properties

Property Value

Service Pressure 250 psi

Operating Temperature Limits -40 F to 125 F

Minimum Rupture Pressure 1250 psi, 5:1 Stress Ratio (ASME Section X)

Structural Material Filament-wound AdvantexTM glass fiber/amine-cured epoxy composite

Liner Material Polymer: HDPE, ASTM D 3350 Cell Classification 345464A End Boss: ASTM B 221 6061-T6 Aluminum (UNS A96061)

Vessel Mounting Buried Underground

Vessel Diameter 40.7 inches (existing steel)

Vessel Length 110.25 inches (existing steel)

Vessel Empty Weight (excluding hardware)

740 lb (existing steel)

Vessel Volume (unpressurized) 500-gallon water capacity

Customer Requirements

The primary design requirement was for a baseline 500-gallon tank. This design is readily scalable to a 250- and 1000-gallon tank in new Lincoln Composites manufacturing line for large vessels. In the process of designing the tank, the impact to both design and manufacturing were considered to mitigate issues associated with the length change. Options for a side port were evaluated to take advantage of existing hardware, which would conceivably help to lower costs if custom-designed hardware were not required. Designing for buried operating conditions per required standard AWWA M-45 utilized the following conditions: (a) burial depth of 24 inches to 48 inches, (b) water table at ground surface, and (c) vehicle traffic load without a slab above the vessel (8000 lb on dual rear tires at 10-inch to 20-inch imprint).


Regulatory Requirements

The tank design was to conform to ASME Boiler and Pressure Vessel Code, Section X: Fiber-Reinforced Plastic Pressure Vessels for the primary design and AWWA Fiberglass Pipe Design Manual M45 to account for the buried installation. This was consistent with the recommendations of the Phase I PERC study, Study of Alternative Tank Materials, Docket 11728. As previously mentioned, NFPA 58 requires tanks to be designed in accordance with metallic tank guidelines. Regulatory authorities accept ASME in general, which permits the use of Section X for building codes, and NFPA 58 could be revised to change regulatory view of the loading stresses on a freshly buried and unfilled tank.

LPG Tank Design Development and Selection

The product designed is a 500-gallon composite propane tank for underground use. Physical dimensions for the tank are specified in Table 2. A survey of product literature for similarly sized steel tanks suggests a 3-foot diameter x 10-foot length to be typical. LPG storage tanks are often installed underground; the tank is designed to be compatible with this type of environment. The proposed design consists of an FRP (fiber reinforced plastic) structural shell with an internal HDPE copolymer liner. The FRP shell is a multi-layered angle-plied filament wound composite structure consisting of continuous glass fiber in an epoxy resin. The liner is constructed of a high-density polyethylene (HDPE) copolymer, which provides a gas containment barrier. Steel tanks typically have a side port for appurtenance hardware. As a consequence of the nature of laminated composites and the filament winding process, a side port presents a significant challenge which can lead to reduced safety margins in the wall and higher manufacturing costs. Thus, the baseline configuration utilizes a port in one head. A hardware configuration has been proposed for accommodating this setup. Other shapes were not considered for this prototypical design. Other shapes could be envisioned that would still use Lincoln Composites’ 41-inch winder limitation, such as cylindrical. However, a 41-inch diameter sphere would yield a tank with only approximately 170 gallons.

Tank Construction

Lincoln Composites’ polymer-lined composite propane tank consists of a high-density polyethylene liner fully wrapped with a glass fiber-reinforced epoxy. A section view illustrating the tank construction is provided in Figure 1.


Figure 1. Tank Construction Section View.


HDPE Copolymer Liner

The HDPE copolymer liner is a non-structural fluid barrier for the containment of liquefied petroleum gas (LPG). It consists of a high-density polyethylene (HDPE) copolymer. By virtue of its low modulus, the liner transfers all loads to the composite shell. The plastic liner is an assembly of two injection-molded heads and an extruded pipe section joined together by butt fusion welds. Nominal wall thickness of the liner is 0.50 inch. This relatively heavy wall thickness is needed due the stiffness required from the liner during the winding process, when the liner serves as the winding mandrel. This method of liner construction was selected because of its high reliability and resistance to permeation and leakage. Typical property values for this material are provided in Table 3.

Table 3. Typical Properties for the High-Density Polyethylene Copolymer

Property Reference Value

Tensile Strength at Yield (2 in/min) ASTM D 638 3300 psi

Elongation at Break (2 in/min) ASTM D 638 > 800%

Flexural Modulus 1 ASTM D 790 120 ksi

Melt Index 2 ASTM D 1238 6.5 g/10 Minutes

Vicat Softening Point ASTM D 1525 259ºF

Brittleness Temperature ASTM D 746 < -180ºF

Density ASTM D 4883 0.944 g/cc

Hardness (Shore D) ASTM D 2240 66

Environmental Stress Crack Resistance3 ASTM D 1693 > 2000 Hours

Environmental Stress Crack Resistance4 ASTM D 1693 > 5000 Hours

Notch Tensile (PENT) ASTM F 1473 > 100 Hours

Notched IZOD Impact Strength (23ºC) ASTM D 256 6 ft-lbf/in

Cell Class ASTM D 3350 PE 345464C 1 2% Secant-Method 1 2 190 C 3 16 kg 3 Condition B, 10% 4 Condition C

An aluminum end boss is inserted into each liner head. The boss at the service end provides a single penetration into the tank for vapor service, filling, liquid level gauging, and the safety relief valve flow path. The boss at the non-service end serves a tail-stock-type function during the fiber winding process as well as providing structural support at confluence point of the fibers over the head. A circumferential keyway in the boss flange provides the mechanism for insert molding the end boss into the liner head. The flange keyway is coated with a thin layer of elastomeric material which serves as a low pressure gasket. The interface is purely mechanical, and is designed such that there is no tendency for the plastic to creep under pressure. This interface is further described in U.S. Patent 5,429,845.


The end bosses are machined from aluminum alloy 6061-T651X extruded bar certified to ASTM B 221. Typical properties for this material are provided in Table 4. The end bosses are anodized to provide a galvanic barrier.

Table 4. Properties of 6060-T651X Aluminum Alloy

Property Value

Yield Strength 38 ksi

Tensile Strength 42 ksi

Elongation 10 %

Tensile Modulus 10,000,000 psi

Shear Strength 20,000 psi

Density 0.098 lb/in3

Poisson's Ratio 0.33

Composite Shell

The composite shell is a multi-layered, angle-plied laminate structure produced by filament winding a continuous band of resin impregnated roving over the polymer liner. The design role of the composite shell is to resolve internal pressure loads and to provide the general strength and durability of the tank. The laminate architecture of the composite shell is shown in Table 5. Nominal wall thickness of the composite shell is 0.43 inch.

Table 5. Composite Shell Layer Architecture

Layer Description Wind Angle, deg Thickness, inch

1 Composite Material 82.6 .062







The composite material is a continuous glass fiber-reinforced epoxy and is the load-carrying element of the tank. Glass fiber provides exceptional strength, lightweight construction, and durability. Glass roving is Owens-Corning 158B Type 30, with the trade name AdvantexTM. This material has improved corrosion resistance and environmental stability over previous forms of E-glass. Fiber volume fraction in the laminate is 55 to 60 percent. Typical properties for these materials are provided in Table 6.

Roving is a collection of several individual fiber threads


Table 6. Properties of Owens-Corning 158B Type 30 Glass Roving


Tensile Strength ASTM D 2343 350,000 psi

Tensile Modulus ASTM D 2343 12,000,000 psi

Yield ASTM D 578 1341 ft/lb

Density ASTM C 693 0.093 lb/in3

The resin system is an amine-cured epoxy formulation developed by Lincoln Composites to address the operating environment and manufacturing considerations for plastic liners. Because the characteristics of this resin are unique and not generally available in commercial systems, Lincoln Composites regards the resin formulation as proprietary. Typical properties of resin are provided in Table 7.

Table 7. Properties of the Lincoln-Formulated Neat Epoxy Resins


Tensile Strength ASTM D 638 13,500 psi

Tensile Modulus ASTM D 638 460,000 psi

Elongation ASTM D 638 7.0 %

Shear Strength ASTM D 732 8,100 psi

Specific Gravity ASTM D 792 1.15

Tg, Dry, DMA ASTM D 4065 246 F

Tg, 24 Hour Water Boil, DMA ASTM D 4065 229 F

Degradation Temperature, TGA ASTM D 3850 680 F

Between the composite shell and the polymer liner, a thin annular rubber shear ply is applied to the flange of the end bosses. By virtue of its low shear modulus, the shear ply precludes frictional contact between the end boss and the composite shell accounting for the differential strain that exists between the two surfaces. The shear ply is formed of a nitrile Buna rubber with an ASTM D 2000 material designation of M2CH-614-A25B14EF31. A coating of paint is applied over external surfaces of the composite shell. The paint improves aesthetics of the tank.

Hardware

Current steel tank designs typically use a sidewall connection location for penetrating the vessel wall. Implementation of a side port in a filament-wound pressure vessel provides several challenges. The first challenge is to add the side port to the liner wall. For a tank with a non-metallic liner and a non-metallic overwrap, the side port addition would involve welding a circular disk, which is manufactured to match the curvature of the tube, into the cylinder section of the liner. The second challenge is the creation of wind patterns that accommodate the disruption to the winding path created by the port. The larger the port, the more difficult it will be to accommodate. The final challenge to this approach is to ensure that the opening in the composite created by the side port retains enough strength to contain the port under pressure. It


is possible to overcome these challenges, but resolution will result in increased expense. As a result of the increased expense of a side wall approach, this Phase II program approach uses a port in the center of the head. This change requires a new hardware approach in the system design. The following is a proposed hardware concept that would be compatible with the proposed tank design.

Filling and Vapor/Liquid Service Interface

The customer/user interface as seen from the surface would be virtually identical to that of a standard underground system. Figure 2 shows an example of a combination valve for ASME underground propane tanks. The example shown is by Sherwood Valve LLC (Niagara Falls, NY). The composite tank interface system was designed using this valve assembly, although other manufacturers’ designs could easily be used as well. The only modification to the standard Sherwood valve assembly is the removal of the float gauge. The horizontal entry into the tank prevents the standard float gauge from being used.

Figure 2. LPG Cluster Valve.

Riser Construction

The proposed riser can be seen in Figures 3 and 4. It consists of hardware for interfacing the valve assembly with the tank. Port connections and pressure containment is handled with use of pipe. The proposal is shown with four pipe components, which include (a) a 72 inch-long pipe


with 2.5-inch tapered pipe thread connections; (b) a 90 degree elbow with 2.5-inch tapered thread connections; (c) a nipple with 2.5-inch tapered thread connections; and (d) a flange with a 2.5-inch taper thread and ASME B16.5 bolted flange connections. Within the pipe components are two tubes. One tube is for vapor space equalization, and the other is a guide for positioning the level sensing equipment. Various material options exist for these components. The proposed system shown uses standard steel pipe. Alternative pipe materials, such as aluminum or composite, could be used for improved corrosion resistance.

Figure 3. Side View Rendering of Preferred Underground Composite Propane Tank

Vapor Space Connection

Use of a side port in the head of the tank creates a situation not found in standard installations. As the liquid level of the propane raises above the side port, the vapor space in the riser is separated from the vapor space in the tank. This would prevent the tank from filling beyond this point. To alleviate this problem, the two vapor spaces must be connected. This is accomplished by routing a tube through the port and into both vapor spaces. This tube is shown in Figure 4.


Figure 4. Proposed Tank System Vapor Space Connection and Side View

Liquid Draw

A liquid draw option is not shown in the images. A liquid draw would require a tube similar to the tube shown for the fluid level sensor equipment guide. The line would need to connect the valve and enter the tank to a suitable depth.

Gusset

A gusset system is shown in the images. The gusset is provided to stabilize the riser relative to the tank. The primary use for this gusset is to reduce the risk of damage at the tank to riser interface during transport. This gusset could be removed or remain for burial in the ground.

Fluid-Level Sensing

The standard method for monitoring fluid level is the use of a float. Due to the orientation of the riser in the proposed system, a standard float system will not work. Several alternative approaches currently under investigation are listed in Table 8. None of the options investigated currently provides an off-the-shelf solution.


Table 8. Fluid Sensing Level Options

Method Description Advantages Disadvantages Pivoting Float

A float is located on the end of a rod that pivots at the opening of the tank. A linkage or cable is then used to transmit float position to through the riser to the surface.

Common method level measurement Reduced cost Provides continuous liquid level Does not require electrical power

No off-the-shelf options available Installation/Removal would require removal of the riser

Float on Rail

Use of a float that can move along a non linear path, such as along a rail.

Reduced cost Provides continuous liquid level Does not require electrical power

Horizontal section through the vessel opening could cause the float to bind up Rail installation through the vessel and riser would be difficult

Unpowered Fiber Optics

Uses fiber optic lines at discrete points to detect liquid level. Would require operator at surface to provide light source to lines.

Potential for reduced cost due to simplicity of design Does not require electrical power Could be uninstalled/ removed from the surface without unearthing the tank.

No off-the-shelf options available Not a technology currently used by sensor manufacturers Only provides levels at discrete points

Powered Fiber Optics

Use fiber optic lines at discrete points to detect liquid level. Light applied automatically and results interpreted electronically.

Potential to be installed/removed from the surface without unearthing the tank.

Off-the-shelf options available, but are not intended to be submerged Requires a power source Only provides levels at discrete points.

Pressure Sensors

One pressure gauge reads the pressure of the vapor space. A second pressure sensor is submerged at the bottom of the tank. Uses the difference in pressure to calculate fluid height.

Potential to be installed/removed from the surface without unearthing the tank Provides continuous liquid level Hardware may be available off-the-shelf

Many off-the-shelf options available may be too large to install through riser/vessel openings Requires a power source The hydrostatic pressure from the propane is not very significant, which may result in poor accuracy.

Guided Wire Radar

A cable is fed through riser into the tank. Microwaves are transmitted down the cable and used to detect the liquid level.

Potential to be installed/removed from the surface without unearthing the tank Provides continuous liquid level Method has been used for measuring Propane Off-the-shelf hardware is available.

Wire would make contact with riser walls and return false signals Off-the-shelf hardware is expensive Requires a power source.

Laser A laser is transmitted down the riser and into the tank. The reflection of the beam is used to detect the liquid level.

Laser could be installed from the surface Provides continuous liquid level Method has been used for measuring liquid levels.

Would require prisms to navigate beam through riser Requires a power source.


Pricing

Tank

Pricing estimates for 250-, 500-, and 1,000-gallon tank sizes are shown in Figure 5.

Hardware

The pricing estimate for hardware pieces is $600. This estimate includes the riser and gusset ($550), and the liquid level sensing system ($50).

Cost Estimates

Cost estimates were made for the 250-, 500-, and 1,000-gallon size composite propane tanks. The distribution of costs across components is shown in Figure 5.

0

1000

2000

3000

4000

5000

6000

7000

250 500 1000

Valve

Riser Piping

Gusset

Liner

Bosses

Resin

Fiber

Figure 5. Cost Estimates for the 250-, 500-, and 1000-Gallon Underground Composite Propane Tanks

$3676

$4406

$5863


Opportunities for Price Reduction

The current design leverages heavily from Lincoln Composite’s current 41-inch diameter tank design. The Lincoln Composite product using the 41-inch design is for containment of much higher pressure. The liner comprises a considerable portion of the tank cost, and is a prime candidate for price reduction. Efforts have been made for this design to scale down the bosses and thus reduce cost; however, it is believed that there are still more opportunities in this area. For the proposed design, the liner is essential a heavy-walled (nearly one inch thick) polyethylene pipe. The wall thickness must be heavy to prevent the large diameter from sagging or flexing during the winding process. The pipe/liner is used as the winding mandrel, upon which the fibers are wound. Other possible designs for supporting the liner, rather than shear bulk, could consider either an internal mechanical "spider" or internal pressurization that would keep a thinner liner in shape during the winding. A one-piece molding of the entire self-supporting liner (with the heads integrally molded with the cylindrical section) would be difficult and much more costly that the extruded pieces of the proposed design. Currently on the market are composite cylinders (10-lb, 20-lb, and 33-lb lift truck) with no liners (http://www.litecylinder.com). This cylinder is made in halves without any end penetrations. The end connections – one in the standard cylinder and multiples for the forklift cylinder – are drilled after the cylinder is wound, epoxy-impregnated, and cured. Thus the winding is not affected by the presence of the end connections. The two-piece cylinder requires precision-ground ends where the two halves are joined. Variations of more than a few 1/1000ths of an inch can substantially reduce the joint strength. Making these ground joints on a diameter of over 40 inches would be very difficult and quite expensive. However for this study, only techniques and materials that were familiar to Lincoln Composites were considered, as the project scope did not include testing of new approaches. For this Phase II report, a relatively low production rate was assumed. An increase in the production rate would reduce the unit cost for the tanks. The pricing for this tank was based on the current winder capacity for 41-inch diameter tanks. This limits production to winding one tank at a time. Investment in additional winders would allow multiple units to be produced simultaneously and to thus reduce the tank price. As a result of the large quantities of materials used to produce tanks of this size, it may be possible to negotiate a reduction of raw material pricing. Table 9 shows the estimated composite tank costs from Figure 5, compared with steel tank costs. Using engineering judgment and experience, Lincoln Composites and the Battelle team have estimated that if efforts addressed in the previous paragraph are successful in reducing the manufacturing costs, costs shown in the column labeled Potential in Table 9 can be achieved. Current (December 2008) steel tank prices are shown for comparison. All prices are FOB factory and include riser, combination valve, and anodes (for steel tank). As shown, there will likely be a premium for a composite tank ($470 for a 250-gallon, $680 for a 500-gallon, and $790 for a 1000-gallon tank) even after significant cost reductions.


Table 9. Comparison of Initial Estimated and Potential Costs After Reductions (U.S. Dollars)

Tank Size Estimated Composite Tank Cost Steel Tank

Cost Gallons Liters Initial Potential

250 950 $ 3676 $ 1700 $ 1230

500 1900 $ 4406 $ 2400 $ 1716

1000 3800 $ 5863 $ 3600 $ 2810

As discussed in the introduction, one of the main drivers for this composite tank design project was the rapidly increasing cost of steel tanks, primarily due to steel price increases. Also noted in the introduction, steel prices did recede in the latter half of 2008. The U.S. price of carbon steel plate is shown in Figure 6 (MEPS, 2009). These price swings will likely continue as international markets have emerged as major consumers of commodity goods, equaling and sometimes exceeding the consumption by the United States. The extreme swings over the past year are unlikely in the near term because of the world-wide economic recession. Likewise, the price of polymeric materials have spiked in the past year, primarily driven by the price of crude oil, as shown in Figure 7 (The Plastics Exchange, 2009). Again, the emergence of countries other than the U.S. has helped magnify typical supply and demand-driven price swings.

200

400

600

800

1000

1200

$/m

etr

ic t

on

Figure 6. United States Carbon Steel Prices, January 1997 to September 2009


0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

0.90

1.00

$$

/po

un

d

Figure 7. United States Carbon Polyethylene Resin Prices, October 2003 to September 2009

These most recent resin price swings did not affect the prices reported here for the composite tank. The prices shown in Figure 5 were in effect in the first half of 2008, which were somewhat lower than the prices shown in Figure 7 ( due to long-term purchasing contracts by Lincoln Composites. Lincoln’s resin costs did increase by mid-2008, but the crude-oil price slide in the latter half of 2008 brought the resin prices back to the same levels as in Lincoln’s cost estimates. However, with oil-based polymers (resin and liner) comprising approximately 60 percent of the material cost of the composite tank, it is likely that the long term costs are likely to track future oil prices. While the composite tank does have desirable features above steel tanks, the possibility of long-term price instabilities may offset these features.

Detailed Design Conclusions

A composite underground tank can be designed for use for propane applications. However, the current design exceeds the Phase I preliminary design weight and price values. This Phase II design has a lower weight than the Phase I steel tank estimates. This reduced weight advantage increases as the tank size increases, as shown in Table 9. As stated above, the composite underground propane tank prices are higher than the Phase I steel and composites tank estimates. It is believed that the price could be reduced through a combination of increased production rate, specialized tooling, and additional development effort.


The differences in the weight and pricing between the Phase I preliminary design estimates and the more detailed Phase II design estimates are a result of detailed production consideration, specifically that of the domes. Phase I estimates were calculated primarily based upon cylinder sections only. Considerable cost and weight are added in order to adequately close the cylinder section by utilizing the domes.


COMPOSITE MATERIALS COMPATIBILITY

In order to lend further credence to the choice of composite materials for the underground propane tank application described in the Detailed Design section, material components were assessed with regard to chemical compatibility with components found in commercial propane. As no data were available in the open literature for the chemical compatibility of the composite system as a whole, individual composite components were considered separately in terms of their propane compatibility. The original materials system selected for the underground propane tank preliminary composite design at the end of Phase I of this program was fiberglass- (E-glass or E-CR glass) reinforced isophthalic polyester. These materials were chosen primarily by considering performance and cost. The detailed design of the current Phase II effort has included emphasis on manufacturing, in addition to the previous two considerations of cost and performance. Our manufacturing partner, Lincoln Composites, recommends a different composite system at this stage of development: fiberglass- (E-CR glass) reinforced epoxy with a high-density polyethylene (HDPE) copolymer liner. Although this composite system is more expensive than that recommended for the preliminary design, there are several reasons for this recommendation. Lincoln Composites has several decades of experience using a hybrid- (carbon and E-CR glass fibers) reinforced epoxy system with an HDPE liner for pressure vessels in the petrochemical, transportation, and aerospace industries. This composite system has been used by Lincoln to manufacture CNG cylinders for decades. As the operating pressure requirements for propane tanks is approximately an order of magnitude less than those for CNG cylinders, the E-CR glass is recommended as a more cost-effective alternative than the combination of carbon and E-CR glass fibers, while also providing the necessary performance. Additionally, there are health and environmental hazard concerns when handling the isophthalic polyester in a manufacturing facility. Isophthalic polyester is used by Lincoln’s sister company, Ragasco*, in its Norway composite cylinder production plant. Additional personnel and environmental protective equipment is required when handling this resin, thus increasing the manufacturing costs. Furthermore, Lincoln Composites already has an ongoing production process in place using the current composite system, so changing the production process to accommodate the resin change would result in significant additional production costs. Lincoln Composites has stated that if production volume of the composite underground propane tanks were to become sufficiently high in the future as to offset the production costs to change resins, then reconsideration of changing the resin to isophthalic polyester would be merited at that time. A literature review was conducted to assess the compatibility based upon published information of the selected tank materials with the compounds in commercial propane. Compositional requirements of commercial propane are referenced in recognized standards (ASTM D1835-05 and GPA 2140-97) and a commercial supplier’s MSDS (AmeriGas, 2009). A previous PERC project that addressed field samples (PERC Docket # 11354, Osborne 2006) was also considered for expected propane compositions. This information is outlined in Table 10. * Lincoln Composites Inc. and Ragasco AS are subsidiaries of Hexagon Composites ASA of Norway


Table 10. Required and Observed Chemical Compositions of Commercial Propane

Component Per ASTM 1835-2005, GPA 2140-

97, MSDS Previously Observed Ranges

(Osborne, 2006)

Propane Predominantly propane; ≥ 87.5% 84 – 99%

Butane ≤ 2.5% 0.2 – 5%

Ethane - 0.3 – 6%

Propylene - 0.1 – 7%

Oil residue 0.05 ml not measured

Ethyl Mercaptan 50 ppm 0.7 – 103 ppm

Sulfur (total, including odorant)

185 ppm 7 – 148 ppm

Hydrogen sulfide > 4 mg/m3 (?) none observed

Methanol 2420 ppm 0 – 1040 ppm

Water no free water; nominally 40 ppm

none observed; 0 to 10 ppm

Chemical resistance data and case history reports from a variety of sources were examined as part of this study to assess the compatibility of the tank materials with the commercial propane components. The compiled component data are listed below in Table 11. As expected, no source was identified that provided compatibility data for the entire composite system, so individual component evaluations were performed. We believe that there are no issues of concern at this point regarding chemical compatibility of the proposed composite components with the chemical components of commercial propane.


Table 11. Chemical Compatibility Data for Phase II Tank Design Components

Component Fiberglass-reinforced Epoxy HDPE

Propane ● ●

Butane ● ●

Ethane ▲ ●

Propylene ▲ ▲

Pentane ▲ Limited

Oil ● (sweet, sour crude)

Limited

Ethyl mercaptan ▲ ▲

Sulfur ▲ ●

Hydrogen sulfide ● ●

Methanol ● ●

Water ● ●

Ammonia No ●

Sodium hydroxide ● ●

Fuel oil ● 73ºF

Natural gas ● ●

Hexane ● ●

▲ No explicit data found.

(Basell Polyolefin, 2005; Cech, 2007; Chevron-Phillips, 2004; FiberGlass Systems, 2005; FiberGlass Systems, 2006; Hexion, 2005; MatWeb, 2007; Newhouse, 1996; Newhouse, 2007; PPI, 2000a; PPI, 2000b; Renaud, 2000; Resolution, 2001; Smith Fibercast, 2008)


CORROSION OF APPURTENANCES

A major advantage for using composite materials versus steel for the underground propane tank design is to eliminate the need for cathodic protection of the tank and the inspections associated with that protection. However, as the appurtenances used in conjunction with the underground propane tanks are also constructed of metal, we undertook a paper study evaluation of candidate appurtenance metals, and the likelihood of corrosion without cathodic protection of the tank. Unsurprisingly, some metals are more corrosion-resistant than others under these conditions, and results are described below. A review was conducted of the construction materials for tank appurtenances and the consequence of their interaction with an underground environment. The main sources of data for the materials of construction of the appurtenances were vendor catalogs and supplier information. The evaluated appurtenances included service valves, relief devices, level gages, regulators, and connection piping. Table 12 summarizes the alloys that are used in most of the appurtenances, and Table 13 lists the nominal composition of the alloys.

Table 12. List of Alloys Used in Appurtenances

Base Metal Form Alloy Name Part Function

Aluminum

Die Cast AA 360 Regulator Bonnet & body

Die Cast AA 360 Cylinder Valve Hand wheel

Forged AA 6061-T6 Regulator Body

Brass Forged C37700 Cylinder Valve Body

Wrought C36000 Regulator Nozzle orifice, cylinder

valve stem

Copper Wrought C12200 Tubing Conduit

Ductile Iron Cast N/A Pressure Relief Valve Manifolds, Body

Stainless Steel Wrought Type 302 Regulator Spring

Steel Wrought Piano Wire ASTM A228

Regulator Spring

Zinc Die Cast ZA-7 Regulator Body, Bonnet


Table 13. Nominal Alloy Composition of Alloys (Compositional data, accessed May, 2007)

Alloy Elemental composition in weight percent

C Al Cu Cr Mn Mg Fe Pb Ni Si Zn

AA 360 — 88 — — — 0.5 2 — — 9 —

AA 6061 — 98 0.3 0.2 — 1 — — — 0.6 —

C12200 — — 99.9 — — — — — — — —

C36000 — — 62 — — — — 3 — — 35.5

C37700 — — 60 — — — — 2 — — 39

Type 302 0.15 — — 18 2 — 70 — 9 — —

Steel, ASTM A228

0.8 — — — 0.5 — 98 — — — —

Ductile iron 3.3 — — — 0.4 — 94 — — 2.5 —

ZA-7 — 4 — — — 0.015 — — — — 96

Several assumptions were made to assess the possible corrosion problems associated with the various materials of construction of the appurtenances listed in Table 12. For the purpose of these analyses, it was assumed that the alloys are uncoated or that the coatings have been breached due to mechanical damage or scratching. Two scenarios are considered, namely that the alloys will be exposed to the worst-case situation of direct contact with the soils surrounding the buried tank, or that the alloys will be exposed to atmospheric conditions above the soil under the dome. The range of temperature was assumed to be from below freezing to 120 F. The range of humidity was also assumed to occasionally reach 100 percent. The general approach was to use data from previous studies and our experience with regard to how some of these alloys behave when exposed to underground and atmospheric environments.

Underground Environments – Corrosion Processes in Soils

The severity of the underground environment depends upon the soil type and several parameters including: (a) the presence of water; (b) the concentration of oxygen in the water; (c) the conductivity of the water; (d) the presence of dissimilar metals in buried appurtenances; and (e) the presence of bacteria that participate in the corrosion process, known as microbiologically-influenced corrosion (MIC). Each of these parameters is briefly discussed in the following paragraphs.

Soil Classifications

One classification method of soils is based on their water storage capacity. Sandy soils do not retain water well, but soils with a large proportion of clay have excellent water retention. Table 14 lists 11 types of soils listed in increasing order of water retention capacity. Extrapolated penetration data for buried pipes in some of these soil types is presented in the Corrosion Prediction Calculations section.


Table 14. Types of Soils Listed in Order of Water Retention Capacity (Corrosion Doctors, 2007)

Soil Type Characteristic

Sand Low

Loamy sand

Sandy loam

Sandy clay loam

Clay loam

Loam Water Retention Capacity

Silty loam

Silt

Silty clay loam

Silt clay

Clay High

Soil Parameters

Several approaches have been used for categorizing the corrosiveness of soils to aid in anticipating the degree of corrosion attack on buried pipe. Corrosivity ratings based solely on soil resistivity are shown in Table 15. Soils are rated from “essentially noncorrosive” to “extremely corrosive.” A more detailed corrosivity scale compiled by the American Water Works Association for cast iron buried in soils is listed in Table 16. This table assigns points to various soil parameters including resistivity, pH, reduction/oxidation potential, presence of sulfides, and degree of moisture. Protective measures are recommended for cast iron pipes if the total points for a particular soil equal or exceed 10. Not all parameters have equal importance. For example, soil pH is important only if it falls below 4 or is greater than 9, which is relatively uncommon.

Table 15. Corrosivity Ratings Based Upon Soil Resistivity

Soil Resistivity, Ohm·cm Corrosivity Rating

>20,000 Essentially noncorrosive

10,000 to 20,000 Mildly corrosive

5,000 to 10,000 Moderately corrosive

3,000 to 5,000 Corrosive

1,000 to 3,000 Highly corrosive

<1,000 Extremely corrosive


Table 16. Numerical Corrosivity Scale (ANSI, 1999)

Soil Parameter Value Assigned Points

Resistivity, Ohm·cm

<700 10

700 to 1,000 8

1,000 to 1,200 5

1,200 to 1,500 2

1,500 to 2,000 1

>2,000 0

pH

0 to 2 5

2 to 4 3

4 to 6.5 0

6.5 to 7.5 0

7.5 to 8.5 0

>8.5 3

Reduction/oxidation potential, mV

>100 0

50 to 100 3.5

0 to 50 4

< 0 5

Sulfides

Positive 3.5

Trace 2

Negative 0

Moisture

Poor drainage, continuously wet 2

Fair drainage, generally moist 1

Good drainage, generally dry 0

Soil Conductivity

The conductivity of the water/soil mixture will be directly related to the concentration of dissolved ionic species such as salts and minerals. This variable will be controlled by the nature of the specific soil surrounding the appurtenance. The availability of water will also be a property of the soil as well as the particular environment, which includes the amount of rainfall and depth of the water table and the burial depth of the appurtenance.

Temperature Considerations

Soil temperature variations at the surface are not likely to have a significant role in affecting appurtenance corrosion rates except when they control the amount of moisture entering the soil, or in the extreme case of completely drying out the soil. Temperature variation of the


appurtenance will decrease as the burial depth increases. It is unlikely that a temperature swing of more than 30 C will occur for most of the buried appurtenances.

Oxygen Concentration

Oxygen concentration surrounding a buried appurtenance is perhaps the most important parameter in determining its corrosion rate. As quoted from the reference by Flitton and Escalante, soils “can be divided into two broad categories: corrosion in undisturbed soils and corrosion in disturbed soils.” (Flitton, Adler, and Escalante, 2003) Corrosion of buried steel in undisturbed soils is always low, regardless of soil type and is controlled solely by availability of oxygen, whereas corrosion of steel in disturbed soils is a strong function of soil conditions. (Flitton, Adler, and Escalante, 2003) Buried appurtenances would certainly belong to the category of disturbed soils when first buried; however, after a period of a couple of years, the soil would revert back to the undisturbed state. The concentration of oxygen surrounding an appurtenance will be controlled by several factors. When the appurtenance is initially buried in the soil, the oxygen content will be relatively high because of the direct path of air leading to the appurtenance. As time progresses and the soil surrounding the appurtenance subsides or collapses around it, the availability of oxygen will depend upon the porosity of the soil. If the water content is high, then the controlling factor may be the diffusion of oxygen from the atmosphere through the water to the appurtenance. Oxygen in the surrounding water in contact with the appurtenance will be consumed during either the oxygen reduction process, or cathodic reactions during corrosion of the appurtenance. As the corrosion product on the appurtenance thickens, the available oxygen will also be expected to decrease with time. These limiting factors usually result in a slowly decreasing corrosion rate or a constant corrosion rate over a long period of time. These rates, in turn, will determine when the time-to-perforation, or failure of the appurtenance, will occur.

Role of Galvanic Corrosion

Galvanic corrosion can play an important role in either increasing or decreasing the rate of corrosion of the appurtenance depending on whether dissimilar metals are attached to it. In a galvanic couple, the more active or anodic alloy will preferentially corrode to protect the more passive or cathodic alloy when both are electrically coupled in the presence of an electrolyte. Most of the appurtenances are constructed of dissimilar alloys with one alloy usually having the majority of surface area. An example is a first-stage regulator that has a body made from die cast zinc, and a nozzle orifice made from brass. In the absence of a protective coating, and while exposed to an electrolyte such as rain water, the zinc will act as a sacrificial anode and will have a higher corrosion rate when attached to the brass orifice. The brass orifice will essentially be protected from corrosion while in contact with the zinc body. The interface of the zinc and brass, however, will show excessive corrosion of the zinc, which may lead to failure of its threaded region over a long period of time.


Role of Crevice Corrosion

Crevice corrosion can occur when a metal is in close contact with another surface (metal or nonmetal) in the presence of an electrolyte. The main reason corrosion occurs in these cases is that the concentration of oxygen in the crevice will be generally less than the concentration in the solution that is outside of the crevice, often referred to as the bulk solution. This differential in oxygen concentration results in a difference in electrochemical potential between the metal surfaces within the crevice and outside of the crevice. The inside surfaces tend to become anodic or electrochemically more active with respect to metal surfaces outside the crevice resulting in accelerated corrosion attack in the crevice. For similar reasons, the pH within the crevice will decrease, forming an aggressive acid solution. The various areas that form a crevice in the various appurtenances include threaded areas, heads of screws or fasteners, and mating surfaces between gaskets.

Role of Microbiologically Influenced Corrosion (MIC)

Corrosion processes accelerated by the presence of certain types of bacteria most often occurs in anaerobic conditions. These conditions will most often be found beneath pipelines in soil or beneath buried appurtenances. The increase in corrosion rates due to MIC can be significant. Anecdotal evidence indicates that pipelines can be perforated on their bottom sides whereas their top sides show much less corrosion damage (Davis, 1999). The presence of these types of bacteria will be controlled almost exclusively by the type of soil surrounding the appurtenance because some soils are better hosts than others for these types of bacteria.

Estimate of Corrosion Rates of Appurtenances in Soils

The following paragraphs summarize the expected corrosion performance of the materials of construction of the appurtenances if they were buried in soils.

Aluminum

For underground applications, the wrought and die-cast aluminum alloys listed in Table 12 are most frequently used for buried pipeline applications. While early applications used uncoated pipes that often last many years, it is now accepted that buried aluminum should be coated because the risk of pitting could not be eliminated, even in high-resistivity soils. It is not common practice to cathodically protect buried aluminum using sacrificial anodes but impressed current protection could be used.


Copper and Brass

Copper exhibits relatively high corrosion resistance to most soils found in the U.S. In cases where the soil is unusually corrosive, it may be necessary to use a protective coating, cathodic protection, or an acid neutralizing backfill such as limestone. For the copper listed in Table 12, it has been found that after three years of burial in a range of dry to wet soils, the uniform corrosion rates were found to vary between 0.05 and 0.35 mils (thousandths of an inch) per year (mpy) (ASM, 2005b). No pitting attack was observed. As was expected, the highest corrosion rates were for soils having the highest conductivity. The brass alloys listed in Table 12 are susceptible to dezincification when exposed to corrosive soils (soil resistivity less than 3,000 ohm•cm). Dezincification leads to porosity and loss of strength of the alloy. While these brass alloys are also susceptible to stress corrosion cracking (SCC), it is unlikely to occur in soils unless ammonia or its compounds such as ammonium nitrate are present.

Ductile Iron

Similar to other metals, the degree of corrosion damage to ductile iron exposed to soils is a function of soil porosity, drainage, and other contaminants. An extensive study done in the 1950s on metals buried in various soils indicated that the penetration depth suffered by gray cast iron ranged from less than 10 mpy to over 80 mpy (Romanoff, 1957). While malleable cast iron (ductile iron) was not studied as extensively as gray cast iron, a visual inspection of the two indicated that they did not differ significantly in terms of the form and extent of their pitting damage. A more reasonable average penetration depth for ductile iron is 10 to 20 mpy.

Stainless Steel

Type 302 will likely perform well in most soils located away from the ocean. A possibility for pitting or crevice corrosion attack exists only in soils where the chloride concentration exceeds 500 ppm. In marine locations where the chloride concentrations can reach 1,500 ppm, the likelihood of pitting attack in this alloy is significant. This alloy, however, is unlikely to be directly in contact with soils because its function as a spring will be located in the interior of a valve or regulator.

Steel

A steel spring directly exposed to soils will quickly corrode, particularly if any moisture is present. It is anticipated that these parts will be shielded from any direct contact with soils.


Zinc

The correlation between various soils parameters and the corrosion performance of zinc is poor. In general, the corrosion rates tend to be lower in soils having high resistivity. Soils having poor aeration such as compacted soils tend to be more corrosive to zinc, and soils having good aeration but high concentrations of contaminants such as chlorides and sulfates can severely pit zinc. Table 17 lists the corrosion rates zinc at various geographic locations in the United States. As shown in Table 17, the corrosion rates range from a low value of 0.006 mpy to a high value of 0.46 mpy.

Table 17. Corrosion Rates of Zinc in Various U.S. Soils (ASM, 2005c)

Soil Type Location Corrosion Rate (mpy)

Bell clay Dallas, TX 0.006

Everett gravelly sandy loam Seattle, WA 0.02

Hempstead silt loam St. Paul, MN 0.04

Houston black clay San Antonio, TX 0.06

Celil clay loam Atlanta, GA 0.067

Lindley silt loam Des Moines, IA 0.11

Fargo clay loam Fargo, ND 0.13

Hanford very fine sandy loam Bakersfield, CA 0.15

Hagerstown loam Lock Raven, MD 0.15

Kalmia fine sandy loam Mobile, AL 0.17

Mahoning silt loam Cleveland, OH 0.19

Gloucester sandy loam Middleboro, MA 0.20

Genesee silt loam Sidney, OH 0.20

Dublin clay adobe Oakland, CA 0.30

Chester loam Jenkintown, PA 0.31

Maddox silt loam Cincinnati, OH 0.43

Allis silt loam Cleveland, OH 0.46

Estimate of Atmospheric Corrosion of Appurtenances Under the Dome

Atmospheric corrosion occurs when a surface is wet due to rain, fog, or condensation. This type of corrosion is a complex process involving a large number of interacting and constantly varying factors, such as weather conditions, air pollutants, and material conditions. The wetting and drying that will inevitably occur on the exposed appurtenances under a shelter during certain seasons will results in higher corrosion rates than if the metal parts were always wet. The combined effect of these factors results in a great variation in corrosion rates. The following paragraphs describe the possible corrosion rates of the materials listed in Table 12 when exposed primarily to atmospheric conditions.


Aluminum

The maximum depth of corrosion attack on aluminum alloy 1100 exposed to industrial and seacoast atmosphere is shown in Figure 8 (ASM, 2005a). While the data were not readily available for the cast and wrought aluminum alloys that are used under the dome, the trend for corrosion would be the same and the actual penetration depths would likely be greater for alloy 6061 because it is less corrosion resistant than alloy 1100. Most of the corrosion penetration is seen to occur on alloy 1100 after only five years of service and will be at least 5 to 6 mils deep.

Figure 8. Depth of Atmospheric Corrosion Attack on Aluminum Alloys 1100 (ASM, 2005a)

Copper and Brass

Copper and brass appurtenances are expected to have relatively low atmospheric corrosion rates of less than 0.12 mpy based on published data, though specific data for two of the brass alloys, namely C37700 and C36000 were not available (ASM, 2005b). The expected trend for these alloys exposed to atmospheric corrosion is shown in Figure 9. The average atmospheric metal loss for brass alloys has been found to be proportional to (time)1/3 and for copper, to (time)2/3. In any case, the total thickness loss for copper alloys exposed to aggressive atmospheric conditions will likely be less than 0.79 mil (20 μm) over a period of 20 years.


Figure 9. Typical Thickness Loss for Brass Alloys in Marine Atmospheres as a Function of Time (ASM, 2005b)

Ductile Iron

The corrosion rate of ductile iron is relatively low in industrial environments (such as those found near manufacturing plants and power plants), and is generally less than 5 mils per year. The atmospheric corrosion rates for ductile iron are primarily determined by the relative humidity and the presence of contaminant gases. Sulfur dioxide and other sulfur-bearing compounds as well as high chlorides near marine environments will increase the attack ductile iron.

Stainless Steel

The atmospheric corrosion Type 302 stainless steel in a typical industrial environment is very low, and samples that have been exposed for two decades in these environments were free from rust stains. However, rust stains were found on coupons after only eight months on samples exposed to a severe industrial environment (such as foundries, refineries, and chemical process plants) that was producing chlorine or hydrogen chloride.

Steel

The atmospheric corrosion resistance of piano wire is poor and in most locations will rapidly corrode unless protected, coated, or otherwise sheltered from the high relative humidity or other atmospheric contaminants. Because the thickness of the spring wire is small, very little reduction in diameter would be needed to result in a failure.


Zinc

Figure 10 is a bar chart showing how the corrosion rate of unprotected zinc corrodes in a sheltered or unsheltered condition in different environments (ASM, 2005c). Interestingly, while the most corrosive situation for zinc is an unsheltered exposure in an industrial environment, the sheltered condition is worse than its unsheltered condition for a marine environment. Accordingly, zinc parts in the dome of a propane tank in a marine environment would have the highest corrosion rates.

Figure 10. Corrosion Rates of Zinc Exposed to Different Atmospheric Environments (ASM, 2005c)

Summary of Corrosion Data and Analysis

Table 18 summarizes the expected performance of the various appurtenances when either buried in soil or under the dome under relatively adverse conditions. The results indicate that the buried condition for the appurtenances is generally more corrosive than the atmospheric exposure condition, especially for the aluminum, brass, ductile iron, steel, and zinc parts. Electrochemically-active materials such as aluminum and zinc are particularly susceptible to galvanic corrosion when coupled to brass component while buried in soil. Traditional magnesium sacrificial anodes would be necessary to protect aluminum and particularly zinc components. If the use of magnesium anodes are not cost-effective, then a robust coating would be needed to ensure long service life if the appurtenances are buried in soils. For a composite tank, the anode would need to be connected directly to the buried appurtenances.


Only steel and possibly zinc components of appurtenances will require coatings to protect them from atmospheric corrosion. The steel components should have satisfactory service life if they are sufficiently sheltered and protected from the atmosphere. Experience has shown that the integrity of the housing protecting the steel is critical in ensuring satisfactory service life of unprotected steel. Particular scrutiny should be given to the quality of the seals or gaskets of the housing as these will likely degrade with time and allow water vapor from the atmosphere to freely enter the protective housings. Change in ambient temperature will result in alternately wetting and drying of components within sealed structure that has compromised seals.

Table 18. Summary of Expected Corrosion Performance for Appurtenances in Soil and Under Dome

Base Metal Alloy Name Buried Atmospheric

Aluminum

AA 360 Coating protection recommended

No coating necessary if sufficient corrosion allowance is used

AA 360

AA 6061-T6

Brass C37700 Coating recommended or

dezincification possible Should perform satisfactorily

C36000

Copper C12200 Satisfactory in most soils Protective patina likely to be formed

Ductile Iron N/A Coating recommended, corrosion rate as high as 20 mpy

No coating necessary away from marine environments

Stainless Steel Type 302 Expected to perform well in non-marine soils, otherwise susceptible to pitting attack

Satisfactory performance unless exposed to severe industrial environment

Steel Piano Wire ASTM A228

Must be sheltered or coated to escape severe corrosion

Must be sheltered or coated to escape severe corrosion

Zinc ZA-7 Coating is recommended though performance is good uncoated

Coating is recommended unless sufficient thickness allowance is made

It is clear from the evaluation undertaken in this task that some alloys used in the appurtenances are at higher risk than others for suffering corrosion damage in service, particularly if they are exposed to soils rather than atmospheric conditions. Only copper and stainless steel do not need to have protective coatings on them in either environment. All other components will need to have a robust coating if they are buried in soils. The use of magnesium anodes to protect appurtenances in soils is probably needed only in the most aggressive soils. The use of sacrificial anodes for appurtenances that are above ground under the dome will not be effective because a continuous electrical path through an electrolyte, such as moist soil or a water film, needs to be contacting the anode and appurtenance for the anode to provide protection. The steel component, which is a spring, will need to be properly sealed within a housing to ensure satisfactory service life. All the metals of construction for the appurtenances, namely aluminum, brass, copper, ductile iron, stainless steel, and zinc may suffer various degrees of corrosion attack


but a sufficiently large corrosion allowance may make the use of coatings unnecessary. The use of coatings for aesthetic reasons, however, will provide an added degree of initial protection for atmospheric exposures.


CONCLUSIONS AND RECOMMENDATION FOR FUTURE WORK

This report presents the design methodology and design details for a 500-gallon (1900-liter) composite tank for underground LPG service. This design, developed in conjunction with Lincoln Composites, Inc. of Lincoln, NE, is based upon previous experience with underground petroleum storage tanks, considering tank static pressure, cyclic pressure caused by temperature and filling, and soil loading. Commercial product cost estimates were also discussed. The current preferred design for a composite propane tank is a polymer-lined composite pressure vessel design and tooling developed for a 41-inch pressure vessel. The composite propane tank consists of an HDPE copolymer liner that is fully wrapped with Type E-CR glass fiber-reinforced epoxy. The baseline composite propane tank is designed for 250 psi with a 5:1 stress ratio and 20 percent margin for internal pressure loads. However, this requirement does not drive the thickness of the current design. Rather, the design thickness is driven by the external underground loading requirements of AWWA M45 Fiberglass Pipe Design Manual. This thickness results in a stress ratio from internal pressure near 7.4:1. In addition to the pressure vessel, the development effort includes a riser design. The proposed riser extends to the ground surface from one of the composite propane tank end openings. This riser includes a vertical pipe housing a tube to connect the vapor space of the vessel and riser, and space for a fluid level sensing system. The riser pipe is topped with a conventional combination valve typically used for this application. A gusset system is included for stabilizing the riser to the vessel during transport. Preliminary marketers’ cost estimates for the tanks are provided for three nominal tank sizes: (a) 250 gallons, (b) 500 gallons, and (c) 1000 gallons. As was shown, there is a price premium for the cost of composite propane tanks compared to that for steel tanks. These prices are based on current equipment and tooling used by Lincoln Composites. Through a combination of increased production rate, specialized tooling, and increased development effort, it is anticipated that the gap between these projected and realized costs will be reduced once serial production is reached. An estimate of the final composite tank prices after significant cost reductions still show a price premium over standard steel tanks ($470 for a 250 gallon, $680 for a 500 gallon, and $790 for a 1000 gallon tank) even after significant cost reductions. For steel tanks, these costs do not include the costs of periodic monitoring or inspections of tanks and/or the cathodic protection system. The cost premium of the composite tanks would be substantially reduced or even eliminated if these periodic inspection costs are added to the costs of the steel tanks. Depending upon the final cost estimate for the composite propane tank, proposed additional work would include further optimization of the propane tank design in order to reduce the tank cost. This could include, for example, consideration of consumable versus non-consumable mandrels for fabrication. The current proposed design uses the HDPE copolymer as a consumable liner, which also adds to the overall expense of the propane tank. If the finalized cost estimate is practical, then building a prototype based upon the detailed design is also proposed.


However, with oil-based polymers (resin and liner) comprising approximately 60 percent of the material cost of the composite tank, it is likely that the long-term costs are likely to track future oil prices. While the composite tank does have desirable features above steel tanks, the possibility of long-term price instabilities may offset these features.


REFERENCES

AmeriGas Propane, L.P., Materials Safety Data Sheet for Odorized Propane, Valley Forge, PA (http://www.amerigas.com/pdfs/safe_eng.pdf, accessed January 2009). “ANSI Standard for Polyethylene Encasement for Ductile-Iron Pipe Systems,” C105/A21.5-99. American Water Works Association (1999). ASM Handbook, Vol. 13B: Corrosion of Aluminum and Aluminum Alloys (2005a). ASM Handbook, Vol. 13B: Corrosion of Copper and Copper Alloys (2005b). ASM Handbook, Vol. 13B: Corrosion of Zinc and Zinc Alloys (2005c). ASME, Boiler and Pressure Vessel Code: Fiber-Reinforced Plastic Pressure Vessels, American Society of Mechanical Engineers, New York, New York (2004). ASTM, Standard D1835-05: Standard Specification for Liquefied Petroleum (LP) Gases, American Society of Testing and Materials, West Conshohocken, PA (2005). ASTM, Standard D2158-05: Standard Test Method for Residues in Liquefied Petroleum (LP) Gases, American Society of Testing and Materials, West Conshohocken, PA (2005). ASTM, Standard D2163-07: Test Method for Analysis of Liquefied Petroleum (LP) Gases and Propene Concentrates by Gas Chromatography, American Society of Testing and Materials, West Conshohocken, PA (2007). ASTM, Standard D2420-07: Standard Test Method for Hydrogen Sulfide in Liquefied Petroleum (LP) Gases (Lead Acetate Method), American Society of Testing and Materials, West Conshohocken, PA (2007). ASTM, Standard D2713-07: Standard Test Method for Dryness of Propane (Valve Freeze Method), American Society of Testing and Materials, West Conshohocken, PA (2007). AWWA, Manual of Water Supply Practices M45 – Fiberglass Pipe Design, American Water Works Association, (2005). Basell Polyolefins, Polyethylene Resistance to Chemicals and Other Media, Technical Bulletin, 2005. Cech, John, Characteristics of Bis F and Phenol Novolac Epoxy Resins: Compositional Differences and Their Effect On Performance, CVC Specialty Chemicals, Inc. website publication, 2007.


Chevron-Phillips Chemical Company LP, Performance Pipe, Driscopipe® 8100 Series Polyethylene Piping Produced From PE3408/PE100 Material, Bulletin PP302 (2004). MatWeb Material Property Database (www.matweb.com), accessed May 2007. Corrosion Doctors website. http://www.corrosion-doctors.org/SoilCorrosion/Frames.htm, Accessed May 2007. Eastern Propane, Underground Propane Tank Installation Guidelines, Eastern Propane, Sparta, NJ, September, 2004. FiberGlass Systems, Chemical Resistance Guide, Bulletin No.E5615 (2005). FiberGlass Systems, Time-Tested Fiberglass Piping Systems From Fiberglass Systems, Bulletin No. C3030 (2006). Flitton, M. K. Adler, and Escalante, E. Simulated Service Testing in Soil, ASM Metal Handbook, Vol. 13A, ASM International, Materials Park, Ohio (2003). Gas Processors Association, Liquefied Petroleum Gas Specifications and Test Methods, GPA Standard 2140-97 (1997). Hexion Specialty Chemicals, Diglycidyl Ether of Bisphenol F (DGEBF) – Performance Properties, Hexion Technical Data Sheet SC0772 (2005). May, Terry, Cathodic Protection, presentation at the NPGA Technology and Standards Committee Fall Meeting, Cincinnati, OH, October, 2005. MEPS (International) LTD, website (http://www.meps.co.uk/allproducts%20steel%20price.htm), accessed September 1, 2009. Muellerleile, Joan, Osborne, Rodney, and Greenwood, Mark. Study of Alternative Tank Materials, Final Report (PERC Docket #11728) Washington, DC: Propane Education & Research Council (2006a). Muellerleile, J. T., Osborne, R. L., and Greenwood, M. E. Study of Alternative Tank Materials for Underground Propane Storage Tanks, Proceedings of the LP Gas Global Technology Conference, Propane Education and Research Council and World LP Gas Association, Chicago, October, 2006b. Muellerleile, J. T., Hindin, B., Osborne, R. L., Cederberg, C. A., Yeggy, B. C., Newhouse, N. L., and Kerr, G., Phase II Study of Alternative Materials for Underground Propane Storage Tanks, Proceedings of the LP Gas Global Technology Conference, Propane Education and Research Council and World LP Gas Association, Seoul, Korea, October, 2008.


Newhouse, Norman L., and Glaesemann, William E., Testing of NGV Fuel Containers in Corrosive Environments, NGV 1996 Conference and Exposition, Putra World Trade Centre, Kuala Lumpur, Malaysia (1996). NFPA 58, Liquefied Petroleum Gas Code, National Fire Protection Association, Quincy, MA, 2008. Nicholson, II, Robert, Personal Communications (including Nicholson, R., and Woodburn, L., Corrosion Is Costly, November, 2004), 2005-2006. NPGA, NPGA #152 – Corrosion Protection for Underground LP-Gas Systems, National Propane Gas Association, Washington, D.C., 1991. NPGA, NPGA #412 – Installation of Underground LP-Gas Systems, National Propane Gas Association, Washington, D.C., 1994. Osborne, R.L., LP Gas Surveys, Final Rreport, (PERC Docket # 11354), Washington, DC: Propane Education & Research Council (2006). Ostroff, J., The High Cost of Metals Prices, KiplingerForecasts.com (article dated April 20, 2006). Plastics Pipe Institute (PPI), TN-4/2000 Odorants In Plastic Fuel Gas Distribution Systems, PPI (2000a). Plastics Pipe Institute (PPI), TR-22/2000 Polyethylene Piping Distribution Systems for Components of Liquefied Petroleum Gases, PPI (2000b). Propane Education & Research Council, Good Practices for the Care and Custody of Propane in the Supply Chain: A Report From Energy and Environmental Analysis, Inc. On PERC Docket 11352, Propane Education & Research Council, Washington, D.C. (2005). Propane Education & Research Council, Composite Propane Cylinder Regulatory Approval Request PERC Docket 10662, Propane Education & Research Council, Washington, D.C. (2004). Renaud, Claude M., and Greenwood, Mark E., Effect of Glass Fibres and Environments on Long-Term Durability of GFRP Composites, Owens-Corning, Granville, OH (2000). Resolution Performance Products, Chemical Resistance Guide For Protective Coatings, 2001. Rey, A., Economics 101: Unquenchable Demand for Steel Raises Prices, Butane-Propane News, p. 58-59, April, 2004. Rey, A., Space-Age Technology Pushes Cylinders to New Heights, Butane-Propane News, p.21, August, 2004.


Romanoff, Melvin, Underground Corrosion, National Bureau of Standards Circular 579 (1957). Smith Fibercast, E5615 Chemical Resistance (http://www.smithfibercast.com/pdf/E5615.pdf), Little Rock, AR, accessed April 2008. Sympson, T., Refurbish, Revitalize, and Reuse, LP-Gas Magazine, p.18, November 2005. The Plastics Exchange website, http://www.theplasticsexchange.com, accessed September 1, 2009. Wheeler, John, This Week in Nuclear, Episode 58: New Nuclear Plant Construction Cost Advantage as Steel Prices Rise, ClearTrend, LLC (May 26, 2008).

Alternative Underground Propane Tank Materials, Final … Alternative...... for pressure vessels....

Documents

Transcript of Alternative Underground Propane Tank Materials, Final … Alternative...... for pressure vessels....