All shell and head joints shall be double-welded butt joints with full penetration. In cases where double welding is impractical, the root pass shall be made by the GTAW process.

All welds for nozzles and manways shall be full penetration through the vessel wall. Where heavy wall vessels with small nozzle diameters are involved, an alternative method of full penetration may be permitted if prior written approval is obtained from the OWNER.

The layout of shell and head plates shall be made in such a manner that the manways, nozzles, and their reinforcing pads are not located in or on any of the weld seams.

Double-welded groove joints shall have their root passes back gouged to sound metal on the reverse side before proceeding with welding on that side.

All single-welded groove joints in nickel alloy, stainless steel, and ferritic steel containing more than two percent chromium shall be welded using a gas tungsten-arc or a gas metal-arc root pass with an inert gas back purge. The back purge shall be maintained for a minimum of two passes.

All welding including supports, clips, and structural parts shall be completed prior to postweld heat treatment.

Permanent welding backing bars other than consumable inserts are not permitted.

Temporary backing bars must match the chemical composition of the base metal being welded. After welding is complete, they shall be removed flush with the base metal without undercutting. All attachment areas shall be examined by magnetic particle or liquid penetrant methods.

Grinding and cleaning of stainless steels and non-ferrous material shall be done only with tools that will not leave detrimental deposits on the base metal; aluminum oxide or silicon carbide grinding wheels and austenitic stainless steel wire brushes shall be used. These tools shall not have been used previously on other than the material to be cleaned.

Peening is not permitted. The use of a needle gun for scale removal is not considered peening.

Welding shall not be performed on cast iron parts. If casting repairs are required, the proposed procedure shall be submitted to the OWNER for approval.

Tack welding may be used for alignment and to maintain root spacing. Tack welds shall be made in accordance with an approved welding procedure using the same electrode that will be used for the root pass and shall be deposited in such a manner as to facilitate incorporation in the weld.

Cracked or broken tack welds shall be chipped or ground out and thoroughly cleaned prior to being fused in with the final weld.

Cracked welds, surface porosity or welds having surface irregularities must be removed before welding resumes. Weld craters shall be completely filled before depositing subsequent weld beads.