METHOD STATEMENT FOR WELDING PIPE

1. PURPOSE

The purpose of this methodology is to provide a systematic control and direction for the activity for the fabrication and welding of piping and structure at Safwan. This method statement provides the expectation to execute work in safe, eco-friendly manner and in compliance to the Client HSE and Quality requirements.

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2. SCOPE

This procedure is applicable for fabrication in Safwan yard for the Construction works for All Project.

3. REFERENCES

• Specification for material and fabrication requirement for CS piping and equipment in sour service.
• Technical specification for piping system.
• Specification for welding and welding inspection of shop and field fabricated carbon steel process and utility piping.
• ASME B 31.3 Process piping.
• DEP 31.38.01.31 Shop and Field fabrication of piping.
• AWS D1.1 Structural welding code.
• DEP 34.28.00.31A Structural steel works.

4. DEFINITIONS

• QHSE                  Quality, Health, Safety and Environment
• QCI                      Quality Control Inspector
• ITP                       Inspection and Test Plan
• WPS                    Welding Procedure Specification
• NDT                     Non-destructive testing
• PWHT                  Post Weld heat treatment

5. RESPONSIBILITIES

In addition to the regular work as per Job description/ regular practice the following activities shall also be carried out.

5.1. Project / Mechanical engineer

Mechanical engineer is responsible to ensure that this procedure is Understood and is being implemented by his subordinates.

5.2. Supervisor/ Foreman

• Ensure that welding equipment, baking oven, quiver is in good condition.
• Ensure welding is done as per the approved WPS and approved for Construction drawing.
• Ensure that weld maps / spool drawings are available.
• Coordinate with QC personnel to study the cause of any reported weld.
• Defects and arrange to take corrective and preventive action.
• Adhere to the QHSE requirements.
• Comply with PTW requirements.

5.3. QC Inspector

• Carry out the inspection as per the Inspection and test plan.
• Approving/ rejecting the item based on inspection.
• Submitting the quality records to the client and getting their approval.
• Responsible to keep records of all inspection related activities.
• Adhere to the QHSE requirements.

5.4. HSE Officer

• Advice the construction crew on HSE aspects and ensure the safety of them.
• Arrange through Job performer for tool box talk covering risk assessment in language understandable by workers.
• Cross checking certified material devices and equipments are used.
• Do weekly, monthly HSE audit.
• Ensure appropriate safety measures are taken as per the risk assessment and control document.
• Adhere to the HSE plan and HSE requirements.

6. Procedure

6.1. General

• Prefabrication will be done at Safwan workshop. Prefabricated spools will be painted with two layers of coating and transported to site for field welding.
• Fabricated spools shall be carefully transport to site. The transported spools will be tied down with ample support to prevent any damage. Tie downs shall be nylon straps and chains shall not be used. By this way it is ensured that no damage is done to painting during transportation to site.
• Ensure no damage is done to painting during transportation to site.
• Whenever the pipes are cut the heat no: shall be transferred to the cut pieces for traceability by paint / permanent marker. Welding shall be done as per the approved procedure, specification and approved for construction drawing.
• Welding machine, ovens and etc. shall be maintained in good condition.
• Approved welders for the particular WPS shall be used for welding.
• Welded surfaces shall be clean and free from grease, oil, paint or other foreign material which are detrimental to welding. 
• Bevels shall be as per the WPS and cleaned for minimum 1” from the welding.
• Peening shall not be performed at any time.
• Tack weld not incorporated in the final weld shall be removed by grinding or other mechanical means. 
• Welding consumables shall be issued, received and handled in accordance with the approved method statement.
• All tools used for working on stainless steel shall be those designated for stainless steel work.
• All flange face shall be protected with plywood / suitable means from mechanical damages during handling or storage. 
• End caps of pipes will be kept in place during storage, moving, fabrication and Erection activities, except when the joint end is actually being worked upon. Flanges and open ends shall be protected at all times. 
• Such protection shall be removed only to permit work to be performed as part of a fabrication or inspection process, after which they shall be again re protected.

6.2. Weather protection:

When the weather does not permit satisfactory workmanship welding shall not be done. On site in windy condition the pipe ends shall be closed to prevent through draughts during welding. Suitable covering using tarpaulin etc. shall be provided. Welding shall not be done when the weld surface is wet / when the area is exposed to rain / strong windy condition.

6.3. Weld Identification:

• Each weld shall be uniquely identified with the joint no: and welder number.
• After completing the weld, the welder shall mark the joint no: & welder no: near the weld using paint or indelible crayon.
• After welding each spool, the line no, spool no & etc shall be marked / tagged on the spool and stocked over wooden sleepers or other suitable material above ground.

6.4. Non Destructive Testing:

Non-destructive testing shall be done as per the approved procedure using approved sub-contractor.

6.5. Alignment Circumferential welds.

• Butt weld alignment shall satisfy the requirement of ANSI B 31.3 and conditions stated below.
• Internal misalignment of pipe work shall not exceed 1.6 mm in order to facilitate welding of the root pass. 
• When a GTAW process is to be used maximum misalignment shall not exceed 0.8 mm. If there is excess misalignment tapering of the internal dia of the thicker member to a taper of 1:4 shall be done. 
• Ensure minimum wall thickness is maintained.
• If misalignment up to 3.2 mm exists, internal grinding or machining may be conducted to improve root alignment, provided the taper doses not exceed 1 in 4 maximums and the minimum required wall thickness is maintained.  
• Misalignment correction shall be done using suitable clamps and heavy hammering or heating of the pipe shall not be done.

6.6. Weld separation

6.6.1. Circumferential welds (Girth welds):

For nominal size of 75mm & above the minimum distance shall be 75 mm. For lesser pipes the minimum distance shall be 4 times of the wall thickness or one pipe dia whichever more is. Welds lesser than the above limit shall be done with the approval of the client and may require PWHT solely at the discretion of the company.

6.6.2. Branch / Nozzle / attachment welds.

Branch / nozzle and other pressure attachment welds shall have minimum 3”.
distance to adjacent pressure welds. Non pressure containing attachment welds shall be separated by 2” from adjacent pressure containing welds.

6.6.3. Longitudinal seams 

Longitudinal seams of adjacent pipes shall be separated by at least 4”.

6.7. Pre-heating, Interpass temperature, PWHT:

Preheating shall be done as per the WPS if high pre heat temperature is specified or else minimum preheat for CS upto 19mm thick is 21°C and > 19mm thick CS is 100 °C. When the base material is below 21 deg C, the material shall be heated to 50 deg C prior to welding. The heating shall be done gradually and uniform manner. The preheat temperature shall be held at least five minutes before welding is commenced & shall be checked using temperature indicating crayons.
Preheating shall be done by using propane torches or by electric resistance and the use of oxy-acetylene torch is not allowed. A minimum width of 3” on both side of the joint shall be preheated. Interpass temperature shall be as per the WPS. If any post weld heat treatment is required as per the WPS the same shall be carried out as per the temperature specification in the WPS. Controlled heating and cooling shall be as per the WPS. The temperature recorded chart shall be submitted to the client for approval. PWHT shall be performed on carbon steel piping if the wall thickness exceeds 19.05 mm.

6.8. Weld sequence:

The weld bead sequence shall be as per the approved WPS. The welding shall be cleaned of all flux, slag and spatter by wire brush, grinding and hand chipping after each pass. The welder shall visually check the welding after every pass for any defects and if any defects found it shall be removed or repaired before the next pass. If any crack is found it shall be informed to the inspector and with his knowledge rework shall be done. After completing welding the adjacent surfaces shall be cleaned of all spatters, slag, flux etc.

6.9. Welding interruption:

Welding for each pass shall be continuous without interruption other than changing electrodes or filler wires or allow welder for changing their position. Specifically root run and hot pass shall be done without interruption. If there is interruption the following action shall be taken. 

• If only 25 % of the weld grove has been deposited, then the weld shall be cutout & recommended for a new preparation. Otherwise the welding shall be recommenced as mentioned below.
• The weld shall be allowed to cool slowly to room temperature. This can be done by wrapping the weld with insulation and allowing the joint to cool in still air. 
• MPI to be carried out prior to welding.
• The weld shall be preheated.

7. REPAIR WELDING:

• Any defects which require repair shall be entirely removed to sound metal. Metal Shall be removed 1” on both side of the defect without substantial removal of the Base metal.
• By grinding, the metal shall be removed and the grove shall be smooth without any undercut. Visual examination and magnetic/dye penetrant test shall be done on the grove. 
• If repairs are done after hydrotest / PWHT the same shall be repeated after repair. Welding repair shall be done only twice. Even after second repair if the weld is not acceptable the weld shall be removed, re beveled and re welded.
• Same NDT technique & acceptance criteria for the original weld shall be done after repair welding.

8. RESOURCES

• Welding machine
• Grinding machine
• Preheating torches with propane gas cylinders
• Holding ovens/baking ovens
• PWHT equipment
• Hiab, Crane
• Cutting tools
• Generator

9. HSE REQUIREMENTS

• Basic PPE.
• Fire extinguishers.
• First Aider with first aid kit shall be available.

10. QA/QC REQUIREMENT ATTACHEMENTS

Quality shall be maintained by ensuring the systematic implementation of this procedure and ensuring quality records are prepared as per the ITP.

Records:

• Piping daily fabrication report P002: MFM 12-M/1-P002
• Fabrication control sheet P003: MQM/P3-005
• Welding electrode control sheet M15: MFM 12-M/1-M15

11. EMERGENCY CONTACT

The following shall be the contact number in case of any emergency.

• Project Manager
• Mechanical Engineer


• QA/QC Engineer


• CM


• HSE