Development by EDF of filler metal and welding procedures for repairing piping systems damaged by Flow Accelerated Corrosion

Authors : Marc Carnus¹, Charles Bonan², 

Company : ¹ Electricite de France EDF
                      Generation Nuclear Division UTO SIS
                   ² Institut de la soudure

Country : France

Topics :

Flow Accelerated Corrosion Piping management

ABSTRACT :

As most of nuclear utilities EDF has to face Flow Accelerated Corrosion (FAC) on carbon steel water/steam piping and vessels shells of  PWR plants. Extensive works have been carried out by EDF, EPRI and nuclear utilities in order to understand FAC damage mechanism and in order to define appropriate inspection programs.

Few years ago EDF  pointed out that welds are a weak point regarding detection of weld damage, understanding of weld FAC damage mechanism and use of FAC resistant filler metal. Several metallurgical expertise  on removed parts from EDF nuclear power plants have shown evidence of selective attack by FAC on butt joints.

In order to protect new welded assemblies EDF has implemented requirements on Chromium content for Carbon steel replacement pipes and filler metal (% Cr >0,15%). One simple solution for FAC resistant filler metal is GTAW carbon steel wire with a minimum %Cr (>0,15)  however such a product is not always commercially available.   Alternative solutions have been studied. These solutions include welding procedure development  using GTAW with different %Chromium content (0,3-0,6-1%) filler metal.  This paper will present  some aspect of EDF experience regarding selective attack of weld and works on  solutions and welding procedures for repairing pipes, pressure vessel components and welds affected by FAC.