Welding

                                                             I.                         

I.       GENERAL

This procedure shall be followed for the fabrication of all types of welded joints of carbon steel and alloy welded pipe joints shall include the following

1) All pipe joints of the longitudinal and circumferential butt welded & socket welded types.

2) Attachment of forging, flanges and other supports to piping.

3) Welded manifold headers and sub assemblies.

4) Welded branch connections with or without reinforcement pads.

5) Joints in welded/prefabricated piping components.

6) The attachments of smaller connections for vents, drains, and other instrument tappings.

II.      APPLICABLE CODES AND STANDARDS.

All welding work, equipments for welding, heat treatment, other auxiliary function and the welding personnel shall meet the requirements of the latest       editions of the following accepted standards and procedures unless otherwise specified in the welding specifications chart and the technical notes attached.

In the case of conflicting requirements, the requirements mentioned in welding specification chart/technical notes shall be applicable

1) Chemical plant and petroleum refinery piping ANSI : B 31.3

In addition, the following codes and specification referred in relevant code of fabrication shall be followed for the welding specifications, consumable      qualification and Non destructive testing procedures.

a) Welding and Brazing qualifications ASME Sec IX

b) Non destructive examination ASME Sec V

c) Material specification : welding rods Electrodes & filler metals  ASME Sec II part C

III.     BASE METAL

1) In general, use of carbon steel, Alloy steel and stainless steel are envisaged the details of the material specification are given in the welding Spec charts.

2) Manufacturers test certificate for every material supplied are to be furnished.

VI.     WELDING CONSUMABLES

1) All the welding consumables necessary for the job execution such as electrodes, filler wire, oxygen, dissolved Acetylene Argon etc.. It should be the approval taken from client/clients representative.

2) The welding electrodes and filler wires supplied should conform the class specified in welding spec.  Also the materials shall be of approved make.

Batch test certificates for all welding consumables shall be furnished to client for   approval.

3) All electrodes shall be purchased in sealed containers and stored property to avoid           deterioration. The electrodes removed from the container shall be stored in   holding ovens at temperature recommended by electrode manufacturer.

4) All low-hydrogen electrodes shall be rebuked at 350° for hour (min) and stored at 80-100 °c before use.

5) Tungsten Electrodes used shall conform to SFA 5.12 spec.

V.      Shielding and purging Gs.

1) Argon used for GTAW welding shall be of 99.995% purity. Purity of the gas shall be certified by manufacturer flow rate shall be established in Wps, normally this rate shall be 7-10 liters per minute.

2) Argon gas of 99.995% shall be used for purging.

3) When GTAW process along or combination of GTAW 7 SMAW process in     used, the purging shall be maintained during rot pan and first filling (Hot pan) to minimize oxidation.

4) Initial pinging shall be maintained for sufficient time to displace air between the           dams.  In no case this should be less than to minutes higher gas pressure shall be avoided after initial pressure, flow to be reduced to such extent that only little positive pressure exists.

5) Gas packing is not recommended for socket type of welding joints.

6) Wherever removal of dams is not possible after punging, water soluble medium is           recommended for dams.  

VI.     EQUIPMENT AND ACCESSORIES

1) Arrangement of minimum No. of welding and cutting equipments, auxiliaries,     and accessories of sufficient capacities is to be done so as to meet the target/schedule.

2) All the equipment for performing the heat treatment, including transformers, thermocouples, pyro-meters, automatic temperature recorders, with suitable           calibration arrangement shall be arranged.

VII.    WELDING PROCESSES

1) Welding of various materials using this procedure shall be carried out generally by

          -   Shielded metal Arc welding process (SMAW)

          -   Gas Tungsten Arc welding process (GTAW)

2) The welding process to be employed is given in our welding spec.

VIII.   EDGE PREPARATION

1) The edge to be welded shall be prepared to meet the joint design requirements by any of the following processes.

a) Carbon Steel Gas cutting, machining or grinding methods shall be used. After gas cutting, oxides shall be removed by chipping or grinding.

b) Low alloy steels (Containing 2½% Cr) Gas cutting, machining or grinding methods shall be used.

c) High alloy steels (S.S), Cupronickel alloys, Aluminum alloys shall be prepared by plasma cutting, machining or grinding. After plasma cutting, surfaces shall be machined or ground finished.

2) Cleaning

a) The ends to be welded shall be properly cleaned by suitable means to remove any surface diet oil, grease, paint, oxidation etc.

b) On completion of each welding pan craters, welding irregularities, slag etc. shall be removed by grinding or chipping.  Wire brushes used for cleaning S.S joins, shall have S.S wire & also the grinding/cutting abrasive wheels shall be of suitable material.

X.      ALIGNMENT AND SPACING

1) Components to be welded shall be aligned and spaced as per the requirements laid           down by applicable code.  Special care must be taken to ensure proper fitting and alignment when the welding is performed by GTAW process.  Flame heating for adjustment and correction of ends is not permitted unless specifically approved by client.

2) A wire spacer of suitable size (diameter) may be used for maintaining the weld root opening while tacking, but it must be removed after tack welding and before laying the  root  bead.

3) For pipe wall thickness 5mm and above the ends to be welded shall be secured together in position with the aid of coupler yokes and ‘C’ clamps to maintain         perfect alignment. yokes shall be detached after the completion of weld, without     causing any surface irregularity

4) Tack-welds, for maintaining the alignment of pipe joints shall be made only by qualified welders.  Since tack welds become part of the final weld material, they should be executed carefully and shall be free from any defects.  Defective weld       tacks should be removed completely before laying any welding.

5) Tacks should be equally spaced. Minimum number of tacks shall be

                 2 tacks - for 2½” and smaller id pipes

                 4 tacks - for 3” to 12 " dia pipes

                 6 tacks - for 14” dia and larger pipes

X.      WEATHER CONDITIONS

1) The parts to be welded and the welding personnel should be adequately protected from rain and strong winds.  In absence of such protection, welding should not be carried out.

2) During field welding using GTAW process particular care shall be taken to prevent any air current affecting the welding process.

XI.     WELDING TECHNIQUE

1) Root Pass

a) Root pass shall be made with electrodes/filler wires recommended in the welding specification chart. For fillet welding, root welding shall be done with consumables recommended for filler pan. The preferable size of the electrodes in      2.5mm dia (12 SWG) but in any care not greater than 3.25mm (10SWG)

b) Upward technique shall be adopted for welding pipe held field with its axis horizontal.

c) The root pass of the butt joints should be executed so as to achieve full           penetration with complete fusion of the root edges. Weld projection quide the pipe shall not exceed 3mm, wherever not specified by the applicable code.

d) Any deviation desired from the recommended welding technique and electrodes           indicated in the welding specification chart should be adopted only after obtaining empress approval of the client/consultant.

e) Welding shall be un-interrupted.

f) While the welding is the progress care should be taken to avoid any kind of movement of the components, Shocks, Vibrations and stresses to prevent occurrence of weld cracks.

g) Preening shall never be done.

2) Joint completion

a) Joints shall be completed using the class of electrodes recommended in the welding specification chart.  Size of the electrode shall not exceed 4mm dia for           stainless steels and alloy steels used for low temperature application.

b) Two weld beads shall not be started at the same pint in different layers.

c) Butt joints shall be completed with a cover layer that would affect good fusion at the joint edges & a gradual notch free surface.

d) Each weld joint shall have a workman like finish.

e) Weld identification work shall be stamped at each joint clearly just adjacent to the weld. Metal stamping shall not used as a standard.  Suitable point shall be used on thin wall pipes for identification.

f) No painting/wrapping coating shall be done over weld position until the joint is accepted

3) Dissimilar welds.

Where welds are to be produced between carbon steels and alloysteels preheat and post heat requirements shall be those specified for corresponding alloy steels     and electrodes shall correspond to AWS E 7016/7018 types.  For welds between        two dissimilar Cr - Mo low alloy steels, preheat and post heat treatment shall be those specified for higher alloy steels and electrodes used shall correspond to those specified for steels of lower alloy contents. For carbon steel or alloy steel to stainless steel welds, use of electrodes E209/E310/E- Nicr Fe 2 shall be made. The welding procedure, electrodes/filler metals, to be used shall have to be of approved make.

XII.    HEAT TREATMENT.

1) Pre Weld heating

a) No welding shall be done without preheating to 10° C when the ambient           temperature is below 10° C

b) Preheating for the various metals shall be as per the attached welding specification chart.

c) Preheating shall be done using resistance or induction heating process.  When permitted, preheating can also be carried out using gas burners utilizing oxy-acetylene or ory-propane gas mixtures with neutral flames.

d) Preheating shall extend uniformly to atleast three times the thickness of material joint but not less than 50mm on either sides of the joint

e) Preheating temperature shall be maintained on the entire length of the weld during           welding.

Temperature indicating crayons or other suitable devices shall be used to check preheating temperature

2) Post Heating

In cases of alloy steel materials such as Cr-mo steels ,if the post weld heat treatment is not carried out immediately after welding the weld joint and adjacent portion of pipe shall be uniformly heated to 300° C.  The temperature shall be      maintained for 2 Hours minimum then wrapped in asbestos cloth or insulation before allowing it to cool to room temperature.  Post weld heat treatment as specified in welding chart shall be carried out later on

3) Post weld heat treatment

a) Post weld heat treatment wherever required for joints between pipes pipe and fittings, pipe & supports shall be carried out as per weld specifications and PWHT procedure.

b) Post weld Heat treatment shall be done in furnace or by using electric resistance           of induction heating equipment as desired.

c) While carrying out local pwht, technique of application of heat must ensure           uniform temperature attainment at all points of the portion being heat treated. Care shall be taken to ensure that the width over which heating being carried out is as per required dimension.

d) Through out the cycle of heat treatment, the position outside the heated band shall be suitably wrapped under insulation so as to avoid any harmful temp gradient at the exposed surface of pipe should not be allowed to exceed 400° C

e) The temperature attained by the portion under heat treatment shall be recorded by means of temperature pyrometers.  Adequate no.of thermos couples hall be   attached to the pipe directly at equally spaced location along the periphery of the joint. The minimum no.of thermocouples attached per joint shall be

                                                             i.      Nos. up to    6”

                                                           ii.      Nos. up to  10”

                                                        iii.      Nos. up to  12” and above.

However the minimum nos. can be increased to specific requirements, if found necessary

f) Automatic temp recorders which have been suitably calibrated shall be employed.  The calibration chart of each recorder shall e furnished to client for approval.

g) Immediately on completion of the Heat treatment, the PWHT charts and records along with test results shall have to be furnished to client for approval.

h) Each joint shall bear the ID No., Which shall be also reflected in isometric drawing and corresponding heat treatment chart.

XIII.   CLEANING

Cleaning of the weld joint all weld joints shall be free from adherent weld slag, spatter, swart, dirt and any other unwauted foreign material.  This can be achieved by wire brushing.  For stainless steels wire brushes with S.S wires shall be used for cleaning.

After completion of above activities the weld joints to be offered fir visual       inspection.