Challenges of Welding the Pipe Spool Modules for AP-1000

AECON was awarded in 2014 a major contract to fabricate piping modules for two new nuclear power plants, Vogtle in Georgia and V.C. Summer in South Carolina. These modules are part of the reactor cooling system of the new advanced pressurized water reactor AP-1000 designed by Westinghouse Company. AECON has extensive experience in fabrication of the piping modules for fossil and petrochemical applications. However, the fabrication of the piping modules for nuclear power plant required welding procedures that would comply with the stringent requirements of ASME Section III, ANSI/AISC N690 Codes and NRC Regulations. The demand to meet the tight schedule for delivering of the modules required welding processes with high productivity and the qualification of new welding procedures along with the optimization of the groove geometry to allow for use of these processes. The submerged arc welding process, SAW, was implemented for welding of the fabricated box beams for both low alloy medium strength steel and very high strength steel (115 ksi material). Pipe welding required development of procedures for various combinations of materials and for dissimilar material joints. The automated orbital welding process was developed and successfully implemented for welding medium and large diameter pipe with restricted access. For welding on non-L grade stainless steel, welding procedures with low heat input were required to be developed to avoid sensitisation of the HAZ during welding. Welders and weld operators for fabrication of the structures and pipe assembles were required to be tested and qualified to perform the welds for restricted access as defined by Regulatory Guide 1.71 which is in addition to the requirements of ASME Section IX Code.