Wednesday, July 1, 2020

WELDING PROCEDURES - OVERVIEW

Method Statement Welding of Piping and Structural Components



1: Welders shall only work within the limit of their qualification range.
2: Welding supervisor/welders shall ensure that "Welding Procedure Specification" (WPS) selection is taken from the approved matrix for each specific line class/application accompanying each WPS.
3: Withdraw consumables only from designated welding stores and endorse initials on the "Welding Consumables Distribution Form" maintained by the issue clerk.
4: Withdraw only sufficient quantities of welding consumable for a four (4) hour period of work.
5: All low-hydrogen welding electrodes shall be maintained in heated "portable rod caddies". The lid of the caddie should be closed following the withdrawal of each withdrawal electrodes.
6: Low-hydrogen electrodes shall only be conveyed to the job site in heated "portable rod caddies".
7: At shift change, all "rod caddies" must be returned to the originating welding store for checking. All issued and unused low-hydrogen electrodes shall be scrapped.
8: The technical requirements of the "Welding Procedure Specification" (WPS) must be followed at all times.
9: Pre-heat and interpass temperatures shall be monitored using "Tempil Stiks" or calibrated "digital" temperature by pyrometers. greater than the nominal wall thickness. ii) For flanges, use the thickness corresponding to two (2) higher wall thickness ranges greater than the nominal wall thickness.
10: Pre-heat values shall be taken calculated and WPS assuming a value of 0.42 CE (Carbon Equivalent). Wall thickness values shall be selected as follows:
a) For pipe-pipe, use the actual wall thickness.
b) For pipe-to-fitting or fitting-to-fitting.
c) For fittings (other than flanges), use the next higher wall thickness range a sufficient period of time to ensure an Oxygen content of less tan 0.5%. When available, "purge monitoring devices" shall be used.
d) Backpurge shall be maintained for a minimum of four (4) passes. Pipe bungs (purge dams) shall be left in place until completion of the joint.
e) The end of partly used filler wire shall be snipped off prior to use.
f) Maintain the tip of the filler rod within the gas shroud during welding to avoid contamination.
g) Interpass temperatures for these materials is critical. The welder shall check the temperature prior to the next pass. All austenitic stainless welds on this project will be tested for "Ferrite" content therefore, cleanliness during fabrication and monitoring of interpass temperatures will have a direct effect on test results.
h) Only approved "iron-free" cutting and grinding disks shall be used.
i) Only approved marking materials (sulphur, chlorine free etc.) are to be used.
j) All material handling devices and equipment shall be adequately protected/lined, to prevent the possibility of carbon "pick-up" (i.e. workbench, transport trucks, supports etc.).
k) Wherever possible, tools shall be colour coded to prevent cross-use with other material types.
11: Pre-head shall be applied through the full thickness of the joint and checked from the opposite side wherever possible.
12: For repair welds, the pre-heating temperature shall be 500 C (1220 F) above that used for the original weld. Maximum pre-heat for repair welding is 1500 C (3020 F).
13: approved WPS. Internal misalignment for butt joints shall not exceed 1.5 mm (1/16").
14: Deposit the root pass and six (6) successive passes or 1/3 of the weld volume prior to interruption (allowing to cool to ambient temperature).
15: Buttering (build-up) is permitted as follows: a) Buttering shall not exceed the lesser of 10 mm or 1/3 base metal thickness. b) If buttering will exceed 10 mm or 1/3 base metal thickness then this shall be witnessed by the customer and the area shall be tested by PT/MT following completion of buttering but before final welding of the joint.
16: Backwelding is permissible for all applications, so long as the same electrodes and process is used as for the fill pass.
17: The following points shall be observed when fabricating/welding stainless and non-ferrous materials:
a) Weld preps and filler materials shall be degreased using an appropriate solvent.
b) Weld prep surfaces shall be buffered using flapper wheels.
c) Argon hoses shall be checked for any loose connections or leakage etc.
d) Fit up geometry shall be in accordance with the applicable, approved WPS.
e) Bridge tacks to be used. Avoid tacking directly on to the adjacent pipe wall. Bridge tack within the fusion faces of the joint wherever possible.
f) Prior to welding, the backpurge shall be set up in accordance with the approved WPS for a sufficient period of time to ensure an Oxygen content of less tan 0.5%. When available, "purge monitoring devices" shall be used.
g) Backpurge shall be maintained for a minimum of four (4) passes. Pipe bungs (purge dams) shall be left in place until completion of the joint.
h) The end of partly used filler wire shall be snipped off prior to use.
i) Maintain the tip of the filler rod within the gas shroud during welding to avoid contamination.
j) Interpass temperatures for these materials is critical. The welder shall check the temperature prior to the next pass. All austenitic stainless welds on this project will be tested for "Ferrite" content therefore, cleanliness during fabrication and monitoring of interpass temperatures will have a direct effect on test results.
k) Only approved "iron-free" cutting and grinding disks shall be used.
l) Only approved marking materials (sulphur, chlorine free etc.) are to be used.
m) All material handling devices and equipment shall be adequately protected/lined, to prevent the possibility of carbon "pick-up" (i.e. workbench, transport trucks, supports etc.).
n) Wherever possible, tools shall be colour-coded to prevent cross-use with other material types.

Piping Material Traceability Chart*

*Click to enlarge image


Engineering and Construction Codes and Standards

ASME IX – American Society of Mechanical Engineers
ASME IX – B 31.3 PROCESS PIPING
ASME IX – B 31.1 POWER PIPING
Material (P numbers) will assist the Welding Engineer to complete the Welding Procedure Specification prior to the mechanical testing of the Procedure Qualification Report.
P-numbers Material Composition
1 Carbon Steel
3 Up to 1/2% Cr and up to 1/2% Mo
4 1 to 2% Cr, 1% Mo Alloy Steel
5A 2 to 3% Cr, 1% Mo Alloy Steel
5B 5 to 10% Cr, 1% Mo Alloy Steel
5C All 5A and 5B Materials heat treated to 85ksi+
6 Martensitic Stainless Steel
7 Ferritic Stainless Steel
8 Austenitic Stainless Steel
9 2 to 5% Ni Alloy Steel
10 Mn-V, Cr-V, 9%Ni, High Cr Alloy Steels
11 Low Alloy Steel, Quenched and Tempered to 95ksi+
21 1.2% Mg or Mn alloy Aluminium
22 1.2% Mn, 2.5% Mg, 0.25% Cu Aluminium
23 1.3% Mg, 0.7% Si, 0.25% Cr Aluminium
25 1.5% Mg, 0.8% Mn, 0.15 Cr Aluminium
31 Copper
32 Admirally, Naval, Aluminium brass, Muntz Metals
33 Cu-Si Alloys
34 Cu-Ni Alloys
41 Nickel
51 Titanium
61 Zirconnium

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