Case of intergranular corrosion fracture caused by improper storage of stainless steel flanges

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Case of intergranular corrosion failure caused by improper storage of stainless steel flanges. Problem: Severe cracks were detected on the neck weld flanges (WNF) of pressure vessels in a certain factory. The crack is parallel to the weld that connects the flange to the vessel nozzle, but there are no cracks on either the nozzle or the vessel. The other container is in the same condition. Flange diameter: 50 cm, material: 304L stainless steel. Metallographic analysis showed that the corrosion failure was intergranular fracture of 304L stainless steel, and microprobe analysis indicated the presence of zinc in the cracks; it was thus concluded that this was liquid metal brittleness (LMC) failure caused by molten zinc. Analysis: Where does zinc come from? Tracking the container manufacturing process revealed that the neck welding flanges used by the container manufacturer were purchased from external suppliers. Due to their large size and weight, the two WNF units were tied to a pallet and placed outside the container workshop. Innocuous zinc-rich paint (with a zinc content of over 90%) is being sprayed near the storage area; the paint powder is blown by the wind to two WNF units, where it settles on the windward side. When WNF is welded to the container nozzles, the welding heat in the heat-affected zone provides the temperature necessary to melt zinc as well as the stresses that cause severe cracks. Measure: The damage caused by the brittleness of liquid metals was discussed in the first section. Therefore, stainless steel at higher temperatures should be protected from coming into contact with zinc and cadmium. This issue should be taken into account both during the manufacturing and use of stainless steel equipment. In this specific case, WNF should be covered or removed.