This specification discusses pressure vessels' fabrication process and technique in compliance with the ASME Boiler and Pressure Vessel Code, Section VIII, Division 1.

This specification in combination with general pressure vessel requirements including Engineering Design and Inspection, Testing, Painting, Marking, Preparation for Shipping and Storage will define the minimum acceptable requirements of unfired pressure vessels suitable for installation in energy industry.

Fabrication

1. General

All Code Category A and B weld joints, including longitudinal and circumferential joints in vessel shells, heads, and nozzles should be full penetration, double butt welds (Type 1).

Where access limitations require the use of single-welded butt joints, the weld detail should ensure a full penetration weld with a smooth internal surface contour, to obtain radiographs equivalent in quality to double butt welded joints.

An acceptable equivalent for Category A and B joints in nozzles, elbows, and single-sided closure seams, is a single welded butt joint with a gas tungsten arc (GTAW) root bead.

Vessels with a wall thickness of 1/2" (13 mm) and less may utilize single butt-welded joints, with prior Buyer approval.

  • The weld detail employed should ensure a full penetration weld utilizing a single "V" or "U" type weld bevel
  • Joints in vessels to be internally coated should utilize double butt welds regardless of thickness, to assure good coating application

All Code Category C and D weld joints, including attachment welds on nozzles, couplings, and manways, should be full penetration welds through the vessel wall, including reinforcing pads where used, and should be welded from both sides.

Where access limitations require the use of single-welded joints, the weld detail should ensure a full penetration weld with a smooth inside surface contour.

Back-up strips should not be used.

Vertical downhill welding should not be permitted.

All semi-automatic or fully-automatic welds should be made utilizing a multi-pass technique.

All non-pressure containing welds, both internal and external, should be full, continuous seal welds.