THE USE OF VANADIUM MODIFIED CHROME MOLYBDENUM STEEL PLATES IN PRESSURE VESSEL FABRICATION

Dillinger Pressure Vessel Symposium

Dillingen, GermanySeptember 16, 2009

© 2008 Fluor Corporation. All Rights Reserved.

Presented by Les Antalffy

Authored By Les Antalffy and Richard Whipple

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Agenda

Historical Background

Benefits Of 2 ¼ Cr-1Mo, ¼ V Steels

ASME Code Allowable Stress Intensity Changes

Reactor Fabrication-Recent Trends

Plate Rolling Capabilities Of Some Fabricators

Manufacturers Of 2 ¼ Cr-1Mo, ¼ V Heavy Plates

Current Status Of 2¼Cr-1Mo-¼V Heavy Wall Vessel Fabrication

Disadvantages Of 2 ¼ Cr-1Mo, ¼ V Steels

Some Fabrication Problems Related To 2 ¼ Cr-1Mo, ¼ V Steels

Recent Reheat Cracking Problems and the Apparent Solution

Summary and Conclusions

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Historical Background

In the late 70’s there was a need to develop high strength steels for reactors in coal gasification projects that resisted hydrogen attack above 454°CJapan Steel Works started their development of modifying 3Cr-1Mo steel by the addition of vanadium.The 3Cr-1Mo-¼V steel developed by JSW was able to resist hydrogen attack up to 510°CFirst two 3Cr-1Mo-¼V commercial reactors for refinery service were completed by JSW for Husky Oil in Canada in 1990In the late 1990’s, the API 941 Committee (Steels For H2 Service at Elevated Temperatures and Pressures) elevated 2 ¼ Cr-1Mo-¼V steel to the same level of hydrogen attack resistance as the 3Cr-1Mo steel From this point on interest developed in using 2 ¼ Cr-1Mo-¼V In 1995 Nuovo Pignone fabricated first 2 ¼ Cr-1Mo-¼V reactor

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The First 2¼Cr-1Mo-¼V Reactor

Courtesy Of GE (Nuovo Pignone)

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Historical Background

Since 1991 almost 650 vanadium modified heavy wall pressure vessels have been built globally or are presently under fabrication.

There has been a recent marked movement away from conventional 2 ¼Cr-1Mo material to 2 ¼ Cr-1Mo, ¼ V material.

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Benefits Of Vanadium Modified Steels

Higher strength / lighter weight / cheaper reactors

Decrease in overall reactor cost when using the new ASME 2007 Division 2 Pressure Vessel Code when the design temperature is not significantly above 454 °C)

Decreased susceptibility to temper embrittlement

Greater resistance to hydrogen attack over the conventional 2¼Cr-1Mo (higher temperatures and higher H2 partial pressures are permissible)

Greater resistance to hydrogen embrittlement

Greater resistance to weld overlay disbonding

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U.S. & EUROPEAN VANADIUM MODIFIED 2 ¼Cr-1Mo PLATE SPECIFICATIONS

ASME SA-542-Type D, Cl.4a

ASME SA-832 Gr22V

European Union EN-10028-2, 13CrMoV9-10

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Recent ASME Code Allowable Stress IntensityChanges

The new 2007 ASME Section VIII Division 2 Pressure Vessel Code permits significantly higher design stress intensities for 2¼Cr-1Mo-¼V steel than the previous edition

– 2004 Edition 169.1 MPa @ 454°C, 163.0 MPa @ 482°C– 2007 Edition 199.8 MPa @ 454°C, 164.6 MPa @ 482°C

The conventional 2¼Cr-1Mo material properties:

– 2004 Edition 127.8 MPa @ 454°C, 110.0 MPa @ 482°C– 2007 Edition 149.8 MPa @ 454°C, 112.0 MPa @ 482°C

This significant allowable stress intensity increase over the 2004 Edition of the Code up to 454°C (18.2%) and over the conventional material (33.3%) will definitely lead to greater future use of the vanadium modified steel

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ASME & EN Code Stress Intensities

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Hydrocracking Reactor Fabrication Recent Trends

Some fabricators have traditionally fabricated vessels with thicknesses above 125 ~150mm using barrel forgings

There has been a growing trend to fabricate vessels with wall thicknesses up to 250 mm using rolled plate, by fabricators who have the ability to roll thick plates. This is especially true in recent times when barrel forging pricing has been high

Use of two piece (maximum) hemispherical heads generally preferred although multiple petal heads are still fabricated

Some fabricators have opted for fabricating reactors using a combined rolled plate and forging solution

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Preformed & Beveled 235 mm Thick Vanadium Modified Plates Ready for Rolling

Picture Courtesy Of ATB Riva Calzoni

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Rolling a 235 mm Thick Vanadium Modified Shell Ring

Picture Courtesy Of ATB

Riva Calzoni

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Hot Rolling A 267 mm Thick Conventional 2 1/4Cr-1Mo Shell Course

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Hot Pressing One Half Of A Two Piece 150 mm Thick Vanadium Modified Hemispherical Head

Photo Courtesy Of Industeel Loire

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150 mm Thick Vanadium Modified Hemispherical Heads Being Normalized

Photo Courtesy Of Industeel Loire

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Quenching A 150mm Thick 4.500 mm ID Hemi Head Section

Photo Courtesy Of Industeel Loire

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4 Petal Heads Are Still Quite Common

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Pressing a Four Piece Head Petal

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Four Piece Head Petals Undergoing Normalizing

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Combined Plate & Forging Fabrication Solution

The combined plate and forging fabrication solution can utilize rolled plate for shell courses and forgings for bed support/quench sections and bottom head/skirt section using a “Y” forging which requires smaller diameter heads

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One Piece Heads

One piece heads are limited by:– Available plate widths– Press or spinning machine capacities– Diameter/thickness limitations

As an example, a 4500 mm diameter head, 150 mm thick requires a blank plate disc ~ 6400 mm in diameterA 10000 ton pressLarge one piece head plates can be forged but are expensive

Thick one piece hemispherical heads are usually not pressed using welded plate

“Y” forgings are used in some instances to reduce head diameters to a size that permits one piece pressing

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It Requires A 10000 Ton Press To Form A 150 mm Thick 4.5 Metre Diameter Head

Courtesy Of Japan Steel Works

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“Y” Forging Permits Smaller Diameter Head and Allows For Skirt To Shell Transition.

Head Attachment Bevel

Skirt Attachment Bevel

Shell Attachment Bevel

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Plate Rolling Capabilities Of Some Key Heavy Wall Fabricators Utilizing Plate Construction

Rolling capacities below are based upon a 3000 mm wide 2 ¼ Cr-1Mo, ¼ V plate rolled to an internal diameter of 4500 mm at 482°C .

– Rolling thickness capacities are dependent on plate widths and rolling temperatures.

– Significantly thicker plates can be rolled at higher temperatures by fabricators with quench facilities

ATB Riva Calzoni 210 mmDillinger 170 mmExterran (Belleli) 200 mmHitachi Zosen 215 mm (10,000 m ton press)Larsen & Toubro 169 mmMangiarotti (Ansaldo) 185 mmWalter Tosto 300 mm (Under Construction)

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Dillinger’s Rolls Under Test Prior To Installation

Courtesy Of Dillinger Hutte

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Manufacturers Of 2 ¼ Cr-1Mo, ¼ V Heavy Plates

Dillinger Hutte (Germany)– 250 mm Thickness, 42 Metric Tons / Plate

ArcelorMittal (Industeel) (France)– 280 mm Thickness, 100 Metric Tons / Plate,

Nippon Steel (Japan)– 200 mm Thickness, 22 Metric Tons/Plate

JFE (Japan)– 215 mm Thickness, 20 Metric Tons/Plate

VoestAlpine (Austria)– 125 mm Thickness, 20 Metric Tons/ Plate

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Current Status Of 2¼Cr-1Mo-¼V Heavy Wall Vessel Fabrication

By June 2009, the following vanadium modified plate vessels had been fabricated or were under fabrication:

– Europe: 62 Thickest, 235mm (ATB, Italy)– Far East: 118 Thickest. 189mm (Hitachi Zosen, Japan)

By June 2009, a total of 394 vessels including forged and plate construction had been fabricated and an additional 200 were under fabrication

Some notable sized forged vessels and their fabricators:– 334 mm thk x 2044 m tons China First Heavy Industries (China)– 256 mm thk x 1661 m tons Japan Steel Works (Japan)– 351 mm thk x 770 m tons Japan Steel Works (Japan)– 347 mm thk x 1020 m tons Kobe Steel (Japan)– 280 mm thk x 2000 m tons GE (Nuovo Pignone) (Italy)

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Disadvantages Of Vanadium Modified Steels

Significantly greater care required during fabrication

Greater sensitivity to weld cracking during fabrication.

Susceptibility to reheat cracking

Intermediate stress relief (ISR) mandatory for highly stressed joints (nozzles, bed supports, etc.)

Greater control required on preheat and interpass temperatures

Higher weld metal hardness compared to conventional 2¼Cr-1Mo

Higher PWHT temperature & longer hold times

Some decrease in fabricator guaranteed toughness for the vanadium modified steel with 54 joule impact energy level at -29°C as opposed to -40°C for conventional 2¼Cr-1Mo

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Crack During Fabrication of 2 ¼ Cr-1Mo, ¼ V Reactor

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Disadvantages Of Vanadium Modified Steels Cont.

The fabrication of reactors from vanadium modified steels requires significantly more care during the fabrication process to avert problems

Globally, there are less than a handful of fabricators experienced and qualified to fabricate heavy wall vessels using vanadium modified steels

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Disadvantages Of Vanadium Modified Steels Continued.

Welding consumables limited to 3 suppliers– Air Liquide Oerlikon (ETC)– Bohler Thyssen– Kobe Steel

Very low toughness of "as welded" weld deposit prior to PWHT.

Successful fabrication requires using experienced fabricators.

Future field weld repairs more difficult to carry out.

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Some Problems that have Occurred During Fabrication Of 2 ¼ Cr-1Mo, ¼ V Reactors

Weld metal cracking from insufficient preheat or not maintaining preheat

Reheat cracking in some 25 reactors

Weld metal not meeting requisite toughness requirements

Cracking from not carrying out ISR for sufficient time for nozzle welds

– low "as welded" toughness

Cracking resulting from weld flaw in nozzle welds – low "as welded" toughness

Cracking resulting from cutting nozzle opening through a bed support weld build up after DHT

– low "as welded" toughness

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Recent Reheat Cracking Experienced By A Number Of Different European & Asian Fabricators

Reheat cracks were discovered between December 2007 and July 2008 in some 25 reactors after ISR or PWHT in multiple SAW longitudinal, circumferential and head welds using manual UT with high sensitivity (4 MHz) 70° probes.Reheat cracks were micro cracks 3mm-10mm in length occurring transversely in the weld metal mainly in clusters, but sometimes individuallySpecial Time Of Flight Diffraction (TOFD) UT procedures were developed in conjunction with using special calibration blocks with 3 mm side drilled holes to find the reheat cracks and manual shear wave UT procedures were then used to characterize the reheat cracksReheat cracks only occurred in SAW welds following heat treatment in constrained production welds but did not occur in production test plate welds

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Grinding the Weld Crown for UT Examination

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TOFD UT Examination Of A Girth Weld

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Indications Of Clusters Of Reheat Cracks

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A Typical TOFD Scan Indicating Reheat Cracks As A Series Of Co-planar Point Diffractors

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Reheat Cracks In Weld Metal Indicated By Dye Penetrant Testing

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Reheat Cracking In Vanadium Modified Welds

As many as 6 independent welding and metallurgical laboratories worked for months trying to isolate the cause of reheat crackingThe ArcelorMittal Industeel laboratory in France determined that there was a significant drop in weld metal ductility as measured by the high temperature Gleeble tensile test at temperatures in the range 600°C - 650°CThe ArcelorMittal Industeel laboratory in France determined that when tramp element levels of lead, bismuth and antimony in the SAW flux satisfied the relationship

Pb + Bi + 0.03Sb ≤ 1.5 ppmthen the decrease in the ductility reverted to the original pre 2008 levels and welds were then found to be reheat crack free

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High Temperature Gleeble Tensile Test Results Indicating A Drop In Ductility At 650°C

Slide Courtesy Of Arcelor Mittal Industeel

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The Apparent Solution To Reheat Cracking

Since August 2008, it was determined that when welding consumables were required to be characterized with Gleeble testing meeting specified minimum ductility requirements and SAW fluxes were specified with ultra low lead, bismuth and antimony contents meeting the established maximum combined content of 1.5 ppm, then the deposited weld metal from welding consumables meeting these requirements did not exhibit reheat cracking during heat treatment

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Summary & Conclusions

Generally pressure vessels have been getting larger, and more complex as more world scale process plants are constructed

At this time some 420 vanadium modified vessels have been fabricated and over 220 vessels are under fabrication

Despite increased fabrication problems, the limited number of qualified fabricators and the limited number of material suppliers, 2 ¼ Cr-1Mo, ¼ V steels reactors are becoming dominant in the heavy wall reactor industry

2¼Cr-1Mo ¼V steel has become the choice for fabrication of reactors with high hydrogen partial pressures and this trend will continue with higher allowable stress intensities permitted by the 2007 ASME Division 2 Code

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Challenges/Recommendations For The 2 ¼ Cr-1Mo, ¼ V Heavy Wall Vessel Fabrication Industry

Improvements in welding consumable “as welded” weld toughness

Improvements in welding consumable weldability

Further development of fabrication and welding technology and improved fabrication methods and fabrication equipment

Development of more experienced fabricators

Expansion by plate suppliers to supply thicker, wider and heavier plates