Following three similar failures of load chains on manually operated geared pulley-blocks of 1-ton capacity, a portion of one of the chains was obtained for examination. The chain was made of mild steel and the links had been electrically butt-welded at one side. In the case of the sample obtained, the failure in service had resulted from fracture of one of the links in the plane of the weld. Six of the other links in the vicinity showed cracks in the welds in various stages of development. Microscope examination showed a crack in an early stage of development and also from an apparently sound link, the prepared surfaces lying in the planes of the links. This examination revealed that the welds were initially defective. Discontinuities were present in both cases adjacent to the insides of the links, of a type indicative of either inadequate fusion or incomplete expulsion of oxide, etc., at the time of the upset, i.e. the pressing together of the ends of the links to complete the welding. It was evident from the examination that the service failures were due to the use of chain that was initially defective.

A steam jacketed autoclave of orthodox design was fabricated from mild steel for a working pressure of 320 psi. The only unusual feature in its construction was a protective layer of weld metal, which was deposited on the internal surface of the upper half of the 1 in. thick shell. The first indication of latent trouble was provided by the bolts which attached the stirring paddles to the shaft and the stationary scraper blades to the shell, either failing in service or breaking off when an attempt was made to remove them. It was the practice to renew them all annually. Microscopic examination of a failed bolt showed the path of the fracture and the secondary cracking associated with it were intergranular, suggesting that failure resulted from stress corrosion. A steel of the rimming type had been used to make the bar from which the bolt was forged. Cracks which originate at the root of threads generally result from fatigue but, in this instance, their intergranular mode of progression indicated that they were due to stress-corrosion. Examination of shell material showed that the cracks in the vessel were wholly intergranular. It was apparent from this evidence that this cracking was also due to stress-corrosion.

A crane hook was stamped S.W.L. 3 tons and, while its main dimensions were in approximate accordance with those specified in B.S. 482 for a hook of this capacity, its shape in some respects was not exactly in conformity with that recommended. At the time of fracture, the load being lifted was slightly under 10 cwts. Fracture occurred away from the normal wearing surface where the hook makes contact with the lifting slings. There was no evidence that fracture was preceded by any appreciable deformation locally or in the region of the failure. A sulphur print, taken on a cross section of the hook adjacent to the plane of fracture, showed the hook was made from a killed steel free from major segregation. Microscopic examination showed the material to be a mild steel in the normalized condition, the carbon content being of the order of 0.25%. Bend tests showed the material at the intrados of the hook would deform in a ductile manner both under slow and impact-loading conditions if in the form of an unnotched test piece, but if notched, it failed in a brittle manner under impact, though not under slow loading.

A welded vessel made of acid resistant 18-8 steel used in a derusting operation started to leak after a long period due to the formation of cracks. The vessel was heated from the outside and did not come into direct contact with the flame. It was surrounded by a casing of unalloyed steel. Where the cracks had not eroded away, it was clear they ran transcrystalline, indicative of stress-corrosion cracking. Because the cracks propagated from the outer surface of the vessel, they were not caused by the derusting agent but by the external atmosphere in conjunction with welding stresses. The narrow gap between vessel and mild steel casing may have aggravated the situation in that it hindered ventilation and evaporation of condensation and favored the absorption and concentration of acids and salts. Contact and crevice corrosion due to deposition of rust from the mild steel casing may have contributed.

A recuperator used for preheating the combustion air for a rolling mill furnace failed after a relatively short service time because of leakage of the pipes in the colder part. The 6 % chrome steel pipes used for the warmer part connected by means of welding with austenitic electrodes to the unalloyed mild steel pipe of larger diam. Visual inspection showed corrosion and deep, trench-like erosion over the entire circumference of the seam on the side of the thicker mild steel pipe. Examination using the V2-A solution for picral etch showed the microstructure of the unalloyed pipe had become coarse-grained and acicular, and the microstructure of the welding seam had become predominantly martensitic as a result of the mixing of the weld metal with the fused pipe material. The chrome steel pipe had become partially transformed to martensite or bainite at the transition to the weld. Thus, the failure occurred due to typical contact corrosion wherein the alloyed welding seam represented the less noble electrode. The martensitic structure may have contributed to the failure as well. Due to the typical nature of the failure, no recommendations were made.