Volume 61, Issue 8

Hydrocarbon leaks were repeatedly found in the client’s refinery. Because of the recurring nature of this failure, the operator approached the authors’ laboratory to get a second opinion on the metallurgical root cause of the failure. It was known from the customer that corrosive species, such as ammonium chloride salt precipitates, are present in the subject diesel hydrotreating unit (DHT). From the findings obtained in the investigation that is the subject of this contribution, the conclusion of the original metallurgical root cause analysis (RCA), namely that the subject piping failed by transgranular chloride-induced stress corrosion cracking (Cl-SCC), could be verified and is indeed correct. The metallurgical root cause of the small bore piping (SBP) failure is chloride-induced SCC. The morphology of the cracking is very distinct and is clearly consistent with transgranular Cl-SCC. A material change to the nickel-base material Alloy 625, already considered by the client, since this alloy is believed to be immune to chloride-induced SCC, would be a good, even though expensive solution. It should be emphasized that there are no metallic materials completely resistant to SCC. If the environment is harsh enough, except for some titanium alloys, i. e., if the source of the chloride ions cannot be eliminated, which is likely the case here, a regular inspection and replacement of these SBP systems might have to be considered. It should further be emphasized that a chloride concentration below 50 ppm is by no means any guarantee for the avoidance of SCC, since chlorides can concentrate in crevices, corrosion pits and such, i. e., the local concentration is what matters, not the local.

A fractured transition side seal retainer, together with an intact piece for reference, was received from the client on December of 2023. The subject part fractured next to the fastening hole, liberating a long ligament that was never found but reportedly caused some damage to hot gas path components downstream of a large gas turbine engine. It is speculated that the subject side seal retainer fractured due to high-stress, not fully reversed bending high cycle fatigue failure. It is recommended to make the design sturdier by considering dampening the long free length of the part, and by specifying a larger fillet radius in the initiation area. Also, over-torquing upon assembly of the subject part should be avoided.

All the jaws of a four-jaw chuck mounted on the faceplate of a large lathe were received by the material testing laboratory to undergo metallurgical failure analysis. Each of the four jaws exhibited cracks in the fillet radius between one of the gripping surfaces and the long horizontal part. The cracks were just visible to the unaided eye und had been discovered by an alert mechanic. One of the jaws was selected for further material analysis for which the crack was opened to undergo fractographic evaluation. The analysis also involved the evaluation of the material using optical emission spectrometry, the preparation of a metallographic sample, and hardness testing. The cracks occurred as a result of repeated overload at the crack initiation sites located in the fillet radius. This was not a single overload event which would not have caused the jaws to crack, but a series of overload events. The situation did not pose a safety hazard to the staff since the soft and tough core of the case-hardened jaws would have retarded, if not stopped, crack growth. A sudden disastrous failure of the jaws by breaking off, for example, and extremely heavy components crashing down as a result were not an imminent threat. This dangerous failure scenario would have been enabled if the jaws had been through-hardened. Instead, casehardening heat treatment had been applied which is the correct choice for this type of component.

ASM International, an organization like DGM, has more than 15,000 members worldwide. The society was founded in 1913 as the Steel Treaters Club in Detroit. Their headquarters have been in the Cleveland, Ohio, area since 1920. ASM International has 6 Affiliate Societies including the International Metallographic Society. In 1952 the need for a focused effort in education in Material Science was recognized and the ASM Materials Education Foundation (ASM Foundation) was established. Their mission is as follows: develop and deploy materials science content and hands-on, minds-on instructional strategies to inspire, engage, and empower future generations to create STEM (Science, Technology, Engineering, Mathematics) solutions for 21 st century challenges. The ASM Foundation has developed a multiprong approach to fulfil this mission and to draw young people to the field of materials science. Materials Camps for Students Teacher Education and Empowerment Mini Camps During Conferences Expansion of Camps to Europe, India and Beyond In addition, the ASM Foundation awards scholarships to undergraduate and community college students in materials science.