The interior surface of a type 316L stainless steel trailer barrel used to haul various chemicals showed evidence of severe pitting after less than 1 year of service. Two sections were cut from the barrel and microscopically examined. Metallographic sections were also prepared at the weld areas and away from the weld zones. Terraced, near-surface pits with subsurface caverns and a high level of sulfur in the pit residue, both indicative of bacteria-induced corrosion, were found. No evidence of weld defects or defective material was present. Testing of the water used at the wash station and implementation of bacteria control measures (a special drying process after washing and use of a sanitizing rinse) were recommended.

A helical compression spring with ten turns made of 1.8 mm thick wire which was under high pressure during tension applied to a rocker arm broke on the test stand in the third turn. The fracture was a torsion fracture that initiated in the highly loaded inner fiber and showed in its origin the characteristics of a fatigue fracture. A longitudinal fold was located at the fracture crack breakthrough which could still be observed at the fourth and fifth turns, where a further incipient crack originated. A metallographic section was made directly next to the fracture path and the fold was cut. It showed decarburized edges in the outer slanted part and this most likely occurred during rolling. The inner radially proceeding part, however, was probably a fatigue fracture originating in the fold. The fracture of this highly stressed spring was therefore accelerated by a rolling defect. In order to decrease the stress, the construction has meantime been modified.

AISI type 321 stainless steel heat exchanger tubes failed after only three months of service. Macroscopic examination revealed that the leaks were the result of localized pitting attack originating at the water side surfaces of the tubes. Metallographic sections were prepared from both sets of tubes. Microscopic examination revealed that the pits had a small mouth with a large subsurface cavity which is typical of chloride pitting of austenitic stainless steel. However, no pitting was found in other areas of the system, where the chloride content of the process water was higher. This was attributed to the fact that they were downstream from a deaeration unit. It was concluded that the pitting was caused by a synergistic effect of chlorine and oxygen in the make-up water. Because it was not possible to install a deaeration unit upstream of the heat exchangers, it was recommended that a molybdenum-bearing stainless steel such as 316L or 317L be used instead of 321.

Three bearing bosses from the cover of scrap shears were sent in for examination. They had torn off the base plate to which they had been welded by fillet welds all around. Two of these were examined. They showed entirely the same symptoms. The bosses had broken away on three sides along the welds. The cleaved fractures in the burned notches propagated partially above and partially below several incipient cracks which may have been fatigue fractures. Metallographic sections showed that the fractures had occurred either at the burned notches near the transition from the weld to the sheet, or else they ran in the sheet material next to the weld. The quality of the welds could not be judged because the opposite fracture pieces to which they adhered had not been sent in. It was concluded that the breakaway of these bosses was at least favored by overheating and hardening.