35 Hot Tapping

Jubail United Petrochemical Company (United) United Olefins Complex Project Jubail, Saudi Arabia

35.

Site Safety Procedures Manual Rev. 1, July, 2001 Page 1 of 5

HOT TAPPING

A.

GENERAL This procedure provides guidelines covering the safety aspects to be considered when welding a hot tap connection onto a pipe or vessel installed in a refinery, chemical plant, or other similar facility, or lines that contained product. It is not a substitute for job planning. A detailed written procedure shall be prepared for each hot tap. This procedure does not apply to hot taps on gas or liquefied petroleum transmission pipelines or service taps on gas distribution mains. These procedures apply to piping and equipment fabricated from ferritic and austenitic steel. Materials such as aluminum, copper, or cast iron are not addressed. Hot tapping shall be performed by qualified professionals who specialize in performing such work on 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 hot tap. The design shall include: • • •

B.

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

METALLURGY Vessels or lines to be hot tapped must be properly inspected for adequate wall thickness and absence of imperfections to minimize the risk of burn-through. Qualified welders shall adhere to controlled welding techniques to prevent overheating. A thorough inspection of each connection area must verify that the metal thickness is adequate for the pressure and temperature involved. There must be no lamination or other imperfections. Hot taps 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 made utilizing applicable regulatory agency standard guidelines. Subsequent passes should be made with a one-eighth inch (1/8”) (3.2 millimeter) electrode diameter or less if the metal thickness does not exceed one-half inch (1/2”) (12.8 millimeters). In many situations, low hydrogen rods may be preferable to reduce the possibility of burn-through. For a wall thickness greater than onehalf inch (1/2”) (12.8 millimeters) where burn-through is not a primary concern, larger diameter electrodes may be used.

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.doc GENERAL SITE CONDITIONS AND SAFETY PROCEDURES

Jubail United Petrochemical Company (United) United Olefins Complex Project Jubail, Saudi Arabia

Site Safety Procedures Manual Rev. 1, July, 2001 Page 2 of 5

Metal Thickness Generally, a minimum base metal thickness of three-sixteenths inch (3/16”) (4.8 millimeters) is recommended for hot tapping. Exceptions to the recommended thickness may be permitted when engineer specifications allow. Welding on thin material could result in overheating and burnthrough. If practical, temporarily reduce the pressure and/or temperature within the equipment to provide 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 be considered. Generally, welding should not be performed on lines or equipment when atmospheric temperature is less than -50°F (-45°C) unless special consideration is given to the base metal characteristics, electrodes, and a method of metal preheating. Hot tap machines should also be checked for suitability of use at low temperatures. Under all circumstances, hot tapping should be limited to the pressure/temperature rating of the machine. Stress Relief Some equipment is unsuitable for hot tapping because the metallurgy or thickness of metal requires 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 must be used. Hot tap fitting and weld rod metallurgy must be compatible with the metallurgy of equipment 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/air mixture within flammable or explosive ranges. In addition, contents of the line or vessel being hot tapped must not contain the following: • • • • •

C.

hydrogen, where the equipment has operated above the Nelson curve limits, because of the 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 initiate such a reaction at the maximum expected pressure. Such reactions could have the potential for causing localized hot spots on pipe walls that could lead to failure.

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

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Jubail United Petrochemical Company (United) United Olefins Complex Project Jubail, Saudi Arabia

Site Safety Procedures Manual Rev. 1, July, 2001 Page 3 of 5

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

D.

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

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

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

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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 the end circumferential welds.

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

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

HOT TAP MACHINES All hot tapping machines must be certified with documented proof of certification for maximum working pressure and temperature rating. The machine must be able to positively retain and remove 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 inside the line or vessel falls within the working limits of the hot tap machine. The seals and materials of the hot tap machine must be compatible with the fluids in the line or vessel and the material of the drill 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 to ensure that they are in satisfactory condition and capable of being left in service, if necessary, in the event of mechanical problems or hot tap valve leakage.

E.

PREPARATION Mounting, assembling, and operation of the hot tapping machine shall be performed by personnel trained for this purpose. Selection of the proper fitting and reinforcement for use in making the hot tap connection shall be based on the proper codes (refer to API). The overall fitting and valve assembly 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 the reinforcement needed. If hot tap diameter is greater than fifty percent (50%) of the run pipe diameter, full encirclement pads or split tees shall be used.

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.doc GENERAL SITE CONDITIONS AND SAFETY PROCEDURES

Jubail United Petrochemical Company (United) United Olefins Complex Project Jubail, Saudi Arabia

Site Safety Procedures Manual Rev. 1, July, 2001 Page 4 of 5

The geometry of the fitting attachment shall be determined before welding. Careful measurements must 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 the cutter in its travel.

If the hot tap is not vertical, a nipple with attached small gate valve shall be welded to the bottom of 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 be implemented before the task is executed. F.

WELDING PROCEDURE • •

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Welding must be performed using welding procedures qualified to the applicable code and specifications 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. Floating roof tanks shall have roofs floating. Welding should not be permitted on the deck of a floating roof except under very carefully controlled conditions. Emergency exit plans shall be in place before starting work on such roofs. Additionally, extreme caution is advised when welding in the following locations of floating roof tanks: -

Inside the pontoon.

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Between the deck and liquid surface near the tank roof gauge float compartment.

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Near the roof seal vent.

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Near the floating roof lift leg vent.

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Between the primary and secondary seals.

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

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Welding shall not be done on empty or partially full lines without proper purging and testing.

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The degree of hazard on lines carrying gas under pressure shall determine if a hot tap can be performed safely.

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Jubail United Petrochemical Company (United) United Olefins Complex Project Jubail, Saudi Arabia

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G.

Site Safety Procedures Manual Rev. 1, July, 2001 Page 5 of 5

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 a right 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, saddles and 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 test valve gaskets and packing and to check attachment weld. Hydrostatic testing shall be done at temperatures below 203°F (95°C). Pneumatic testing, using air or nitrogen, shall be done at temperatures 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 for testing. These additional tests shall not substitute for the pneumatic test.

RESPONSIBILITY It shall be the Project/Site Manager's responsibility to review and justify the need for performing hot taps (ensure alternatives have been exhausted) and for assuring that the Hot Tap Permit has been completed and signed by all designees. The Project/Site Manager is responsible for ensuring that the people required to perform the hot tapping work are trained and qualified.

H.

EXCEPTIONS TO THIS POLICY All exceptions must be approved and signed-off by a Registered Professional Mechanical Engineer in conjunction with the Project/Site Manager and Owner.

ATTACHMENT A: HOT TAP PERMIT

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.doc GENERAL SITE CONDITIONS AND SAFETY PROCEDURES