A type 17-4PH stainless steel tube exhibited brown discoloration after a pickling operation. EDS analysis of the extracted substance revealed relatively high levels of iron and chromium, along with lower amounts of aluminum, silicon, sulfur, chlorine, calcium, manganese, and nickel. The iron, chromium, and nickel are likely in the form of dissolution products from the pickling solution. FTIR analysis revealed the presence of polypropylene and poly(ethylene:propylene). The EDS results showed that the discoloration of the tube was associated with oxidation products of the tube material, as well as adherent organic residue. Analysis by FTIR of the residue revealed detectable levels of two polymeric substances, which were later determined to be construction materials of the pickling tank. It was recommended that more frequent cleaning and/or replacement of the pickling solution be put into place and another type of tank material be considered.

Two AISI type 316 stainless steel components intended for use in a reducer section for sodium piping in a fast breeder test reactor were found to be severely corroded—the first soon after pickling, and the second after passivation treatments. Metallographic examination revealed that one of the components was in a highly sensitized condition and that the pickling and passivation had resulted in severe intergranular corrosion. The other component was fabricated from thick plate and, after machining, the outer surface represented the transverse section of the original plate. Pickling and passivation resulted in severe pitting because of end-grain effect. Strict control of heat treatment parameters to prevent sensitization and modification of pickling and passivating conditions for machined components were recommended.

The power-type counterbalance spring, formed from hardened-and-tempered carbon steel strip and subsequently subjected to phosphating treatment, fractured at the two locations during fatigue testing. A rust colored dark band at the inside edge of the fracture surface was disclosed during investigation. Etch pits were revealed by the cleaned surface which were never observed on properly phosphated coating. It was interpreted that the spring had been subjected to an abnormal acid attack in pickling or phosphating which had resulted in considerable absorption of hydrogen by the metal and hence embrittlement. The part was concluded to have cracked during phosphating or excessive acid pickling before phosphating.

An AISI 4340 Ni-Cr-Mo alloy steel draw-in bolt and the collet from a vertical-spindle milling machine broke during routine cutting of blind recesses after relatively long service life. Based on fracture surface features, it was suspected that the draw-in bolt was the first to fracture, followed by failure of the collet, which shattered one of its arms when it struck the work table. Scanning electron microscopy showed the presence of hairline crack indications along grain facets on the fracture surface of the bolt. This, coupled with stepwise cracking in the material, generally raised suspicion of hydrogen embrittlement. It appeared that fracture in service progressed transgranularly to produce delayed failure under dynamic loading. The pickling process used to remove heat scale was suspected to be the source of hydrogen on the surface of the bolt. The manufacturer was requested to change its cleaning practice from pickling to grit blasting.

Two new chrome-plated CDA 377 brass valves intended for inert gas service failed on initial installation. After a pickling operation to clean the metal, the outer surfaces of the valves had been flashed with copper and then plated with nickel and chromium for aesthetic purposes. One of the valves failed by dezincification. The porous copper matrix could not sustain the clamping loads imposed by tightening the pressure relief fitting. The second valve failed by shear overload of the pressure relief fitting. Overload was facilitated by a reduction of cross-sectional area caused by intergranular attack and slight dezincification of the inner bore surface of the fitting. Dezincification and intergranular attack were attributed to excessive exposure to nonoxidizing acids in the pickling bath.

Brittle intergranular fracture, typical of a hydrogen-induced delayed failure, caused the failure of an AISI 4340 Cr-Mo-Ni landing gear beam. Corrosion resulting from protective coating damage released nascent hydrogen, which diffused into the steel under the influence of sustained tensile stresses. A second factor was a cluster of non-metallic inclusions which had ‘tributary’ cracks starting from them. Also, eyebolts broke when used to lift a light aircraft (about 7000 lb.). The bolt failure was a brittle intergranular fracture, very likely due to a hydrogen-induced delayed failure mechanism. As for the factors involved, cadmium plating, acid pickling, and steelmaking processes introduce hydrogen on part surfaces. As a second contributing factor, both bolts were 10 Rc points higher in hardness than specified (25 Rc), lessening ductility and notch toughness. A third factor was inadequate procedure, which resulted in bending moments being applied to the bolt threads.

Two freshwater tanks (0.81 mm (0.032 in) thick, type 321 stainless steel) were removed from aircraft service because of leakage due to pitting and rusting on the bottoms of the tanks. One tank had been in service for 321 h, the other for 10 h. There had been departures from the specified procedure for chemical cleaning of the tanks in preparation for potable water storage. The sodium hypochlorite sterilizing solution used was three times the prescribed strength, and the process exposed the bottom of the tanks to hypochlorite solution that had collected near the outlet. Investigation (visual inspection, 95x unetched images, chemical testing with a 5% salt spray, chemical testing with sodium hypochlorite at three strength levels, samples were also pickled in an aqueous solution containing 15 vol% concentrated nitric acid (HNO3) and 3 vol% concentrated hydrofluoric acid (HF) and were then immersed in the three sodium hypochlorite solutions for several days) supported the conclusion that failure of the stainless steel tanks by chloride-induced pitting resulted from using an overly strong hypochlorite solution for sterilization and neglecting to rinse the tanks promptly afterward. Recommendations included revising directions for sterilization and rinsing.