35 Hot Tapping

Jubail United Petrochemical Company (United) Site Safety Procedures ManualUnited Olefins Complex Project Rev. 1, July, 2001Jubail, Saudi Arabia of 5

H:\06700320 EO-EG\101\EOEG ITB\ITB FINAL IFC\Part III Project Execution Instructions\4.0 Safety and Security\4.5 Safety Procedures Manual\35_-Hot-Tapping.docGENERAL SITE CONDITIONS AND SAFETY PROCEDURES

35. HOT TAPPING

A. GENERAL

This procedure provides guidelines covering the safety aspects to be considered when welding ahot tap connection onto a pipe or vessel installed in a refinery, chemical plant, or other similarfacility, or lines that contained product. It is not a substitute for job planning. A detailed writtenprocedure shall be prepared for each hot tap.

This procedure does not apply to hot taps on gas or liquefied petroleum transmission pipelines orservice taps on gas distribution mains. These procedures apply to piping and equipment fabricatedfrom ferritic and austenitic steel. Materials such as aluminum, copper, or cast iron are notaddressed.

Hot tapping shall be performed by qualified professionals who specialize in performing such workon a frequent basis.

Client representatives should be included from initial designs through hot tap completion (safety,construction, operations, maintenance, etc.)

An engineered design with a drawing approval cycle shall be implemented for the proposed hottap. The design shall include:

• metallurgical analysis, including wall thickness, determination by ultrasonic test (UT);• in-process controls and inspections to assure conformance to design;• approval of Contractor/Subcontractor procedures; and a review and approval by Owner

B. METALLURGY

Vessels or lines to be hot tapped must be properly inspected for adequate wall thickness andabsence of imperfections to minimize the risk of burn-through. Qualified welders shall adhere tocontrolled welding techniques to prevent overheating.

A thorough inspection of each connection area must verify that the metal thickness is adequate forthe pressure and temperature involved. There must be no lamination or other imperfections. Hottaps should only be made in lamination-free areas with adequate metal thickness.

Burn-Through Prevention

To minimize the possibility of burn-through, the first weld pass to the equipment should be madeutilizing applicable regulatory agency standard guidelines. Subsequent passes should be madewith a one-eighth inch (1/8”) (3.2 millimeter) electrode diameter or less if the metal thicknessdoes not exceed one-half inch (1/2”) (12.8 millimeters). In many situations, low hydrogen rodsmay be preferable to reduce the possibility of burn-through. For a wall thickness greater than one-half inch (1/2”) (12.8 millimeters) where burn-through is not a primary concern, larger diameterelectrodes may be used.



Metal Thickness

Generally, a minimum base metal thickness of three-sixteenths inch (3/16”) (4.8 millimeters) isrecommended for hot tapping. Exceptions to the recommended thickness may be permitted whenengineer specifications allow. Welding on thin material could result in overheating and burn-through. If practical, temporarily reduce the pressure and/or temperature within the equipment toprovide an additional safety factor while welding takes place.

Metal Temperature

If the metal temperature is less than 50°F (10°C), heating the weld area before welding should beconsidered. Generally, welding should not be performed on lines or equipment when atmospherictemperature is less than -50°F (-45°C) unless special consideration is given to the base metalcharacteristics, electrodes, and a method of metal preheating. Hot tap machines should also bechecked for suitability of use at low temperatures. Under all circumstances, hot tapping should belimited to the pressure/temperature rating of the machine.

Stress Relief

Some equipment is unsuitable for hot tapping because the metallurgy or thickness of metalrequires stress relieving, which normally cannot be done while the equipment is pressurized.Special treatment is required for high tensile strength alloy steels; special-welding electrodes mustbe used. Hot tap fitting and weld rod metallurgy must be compatible with the metallurgy ofequipment to be tapped.

Chemistry of Line or Vessel Contents

The oxygen level within the equipment must be controlled to prevent the formation of a vapor/airmixture within flammable or explosive ranges. In addition, contents of the line or vessel being hottapped must not contain the following:

• hydrogen, where the equipment has operated above the Nelson curve limits, because ofthe possibility of hydrogen molecules attaching to the metal;

• vapor/air or vapor/oxygen mixtures within flammable or explosive ranges;• acids, chlorides, peroxides, or other chemicals likely to decompose or become hazardous

from the heat of welding;• caustic or amine if the concentration and temperature are such that the fabrication

specifications call for stress relieving; and

• certain unsaturated hydrocarbons that may experience exothermic decomposition reaction(ethylene, for example) if the metal temperature resulting from hot tapping could initiatesuch a reaction at the maximum expected pressure. Such reactions could have thepotential for causing localized hot spots on pipe walls that could lead to failure.

C. REQUIREMENTS

Hot work on pipelines and other operating equipment shall not be applied for pressures less thanatmospheric or greater than seven hundred (700) pounds per square inch per grade (psig) and



temperatures less than 70°F (20º) or greater than 600°F without additional extensive engineeringand/or consultation with appropriate industrial specialists.

• The pipe, tank, or vessel walls must be at least the minimum thickness for the designtemperature and pressure plus three-thirty-seconds of an inch (3/32”), but in no case lessthan three-sixteenths of an inch (3/16"). The thickness must be confirmed by ultrasonictesting.

• The metallurgy of the pipe, tank or vessel shall be fully determined prior to welding.

• Hot taps shall not be performed upstream of rotating equipment without filters or traps toretain cuttings.

• The chance of blow through is greatest on welds running longitudinal to the pipeline.Therefore, on full encirclement fittings the only welds made directly to the pipe are theend circumferential welds.

• Minimum velocity (flow) of the fluid/gas shall be specified in the job plan for each hottap.

• Pipelines with high flow rates or refrigerated liquids tend to result in too rapid quenchingof the weld which may contribute to weld cracking problems. Bolt-on tees, suitable forthe service, may be used where weld cracking or stress relief is a problem.

D. HOT TAP MACHINES

All hot tapping machines must be certified with documented proof of certification for maximumworking pressure and temperature rating. The machine must be able to positively retain andremove the blank or coupon. They may be powered by hand, air, hydraulic fluids, or electricity.

A hot tap machine can be considered suitable if the pressure and temperature of the medium insidethe line or vessel falls within the working limits of the hot tap machine. The seals and materials ofthe hot tap machine must be compatible with the fluids in the line or vessel and the material of thedrill or cutter must be suitable for effective penetration of the metal of the pipe or vessel.

Before hot tapping is attempted, the machine, cutter and pilot bit should be carefully inspected toensure that they are in satisfactory condition and capable of being left in service, if necessary, inthe event of mechanical problems or hot tap valve leakage.

E. PREPARATION

Mounting, assembling, and operation of the hot tapping machine shall be performed by personneltrained for this purpose. Selection of the proper fitting and reinforcement for use in making the hottap connection shall be based on the proper codes (refer to API). The overall fitting and valveassembly length must not exceed the machine boring bar maximum travel. Weldolets, weld-ends,split tees, saddles, nozzles, branch-o-lets, or plain meters may be used depending on thereinforcement needed. If hot tap diameter is greater than fifty percent (50%) of the run pipediameter, full encirclement pads or split tees shall be used.



The geometry of the fitting attachment shall be determined before welding. Careful measurementsmust be made to assure that:

• tapping machine has sufficient overhead clearance for its full travel;• the valve is sufficiently deep so that the pilot bit clears the valve seat when retracted;• the tapping machine cutting rod is of sufficient length to cut entirely through the pipe, vessel,

or tank wall;• for piping, the cutter does not cut the opposite wall of the pipe;• the cutter head is of sufficient depth to cut heavy wall vessels and pipes; and• the proper angularity (if kept between the nozzle and the wall) and all elements (seat rings,

bolt circles, etc.) are concentric with each other to prevent the jamming or obstruction of thecutter in its travel.

If the hot tap is not vertical, a nipple with attached small gate valve shall be welded to the bottomof the tapping valve for blowing or washing cuttings out of the seating area.

A Safety Action Plan, Job Safety Analysis and Safety Task Assignment (STA) procedures shall beimplemented before the task is executed.

F. WELDING PROCEDURE

• Welding must be performed using welding procedures qualified to the applicable code andspecifications and welders qualified to the welding procedures, code, and specification.

• On storage tanks the liquid level shall be at least three (3) feet above any welding. Floatingroof tanks shall have roofs floating. Welding should not be permitted on the deck of a floatingroof except under very carefully controlled conditions. Emergency exit plans shall be in placebefore starting work on such roofs. Additionally, extreme caution is advised when welding inthe following locations of floating roof tanks:

- Inside the pontoon.- Between the deck and liquid surface near the tank roof gauge float compartment.- Near the roof seal vent.- Near the floating roof lift leg vent.- Between the primary and secondary seals.

• Nozzles shall be beveled 45° - 50° from the outside. The entire weld on carbon steel nozzlesshall be made with American Welding Standards of Engineering (A.W.S.E.) -7018 electrodesor equivalent.

• Nozzle pad shall be air or nitrogen tested, and soaped for leaks.• Hot taps should be performed on flowing lines with exceptions requiring attention as below:

- Static lines shall be full and properly vented if run is less than twenty (20) feet.- Welding shall not be done on empty or partially full lines without proper purging and

testing.- The degree of hazard on lines carrying gas under pressure shall determine if a hot tap can

be performed safely.



• Hot taps within eighteen inches (18”) of a pipe anchor, expansion joint, expansion loop,flanged connection, or threaded connection shall be avoided.

• The hot tap fitting shall be full-fusion welded to the equipment to be tapped (normally) at aright angle. The fitting shall be contoured to the shape with a nozzle bevel and one-eighth inch(1/8”) gap to permit full penetration weld. Longitudinal welds on encirclement tees, saddlesand sleeves shall not tie onto pipe.

• Before the tap is made, a test on the branch shall be carried out with valve in position to testvalve gaskets and packing and to check attachment weld. Hydrostatic testing shall be done attemperatures below 203°F (95°C). Pneumatic testing, using air or nitrogen, shall be done attemperatures above 203ºF (95ºC). Soaping for leaks shall be used for pneumatic testing.

• Additional testing such as radiograph, dye penetrant, or magnetic particles may be used fortesting. These additional tests shall not substitute for the pneumatic test.

G. RESPONSIBILITY

It shall be the Project/Site Manager's responsibility to review and justify the need for performinghot taps (ensure alternatives have been exhausted) and for assuring that the Hot Tap Permit hasbeen completed and signed by all designees.

The Project/Site Manager is responsible for ensuring that the people required to perform the hottapping work are trained and qualified.

H. EXCEPTIONS TO THIS POLICY

All exceptions must be approved and signed-off by a Registered Professional MechanicalEngineer in conjunction with the Project/Site Manager and Owner.

ATTACHMENT A: HOT TAP PERMIT

35 Hot Tapping

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