This paper deals with the hydrogen embrittlement (HE) of a CrMoV steel where more than 0.2% vanadium is alloyed to CrMo steel. The standard CrMo steel (JIS SCM435) is prone to HE in SSRT (slow strain rate tension test), exhibiting inter-granular (IG) fracture. The vanadium addition makes the steel resisting to HE by suppressing IG fracture. With more hydrogen absorption, not being referred ordinarily, the steel undergoes ductile fracture and the fracture strength falls into smaller value. This fracture initiates as IG fracture, and spreads with dimple-like ductile fracture on PAGB (prior austenitic grain boundary), which has been yielded through the accumulation of vacancy type lattice defects during SSRT. Both IG fracture and dimple-like ductile fracture are derived from the refined grain size with vanadium addition. The vanadium addition also acts to reduce the film-like cementite along PAGB to avoid IG fracture. The CrMoV steel may fracture in CLT (constant load tension test) just like the case of SSRT; the fracture strength may become somewhat higher than that of SSRT with more hydrogen absorption. The steel can be applicable to various usage like bolt, spring or hydrogen gas vessel, and it works in diverse ways for preventing HE.

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When structures and products made with CFRP laminate composite plates get some local damage accidentally then need to be repaired, the scarf repair is done generally.
In this study, the influence of the difference in the processes of scarf repair used in the structures of CFRP laminate composites on the tensile and compressive strength of the repaired parts were investigated and discussed. Two processes of scarf repair were used. One (ideal repair) was carried out under a sufficient condition having cleanroom and autoclave, etc. in a repair factory of aircraft maker and other (field repair) was done using some simple instruments in a laboratory expecting a field repair. Two ideal repair models (one of them was given an impact damage to its repair part) and one field repair model were prepared and each repair models were examined by tensile test and compressive test under the condition of room temperature in air, these strengths and fracture modes were discussed comparing among the three kinds of repair models. The following results are obtained.
⑴ The field repair model showed lower tensile strength by about 18 % compared with that of the ideal repair model. ⑵ For the ideal repair model with impact damage, in tensile test, its damage starting from local damage part by impact load generates the separation in adhesive layer. Thus, its tensile strength decreases by about 20 % compared with the ideal repair model without impact damage. ⑶ Both of two ideal repair models with/without impact damage and a field repair model showed almost same values in these buckling stress and compressive failure stress. ⑷ In case of that the compressive load acts in practical structure with scarf repair, the design of scarf repair should be considered with the influence of the load due to the out-of-plane deformation, which leads to separation in the adhesive layer.

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On June 21, 2019, a piping elbow of the hydrofluoric acid alkylation unit ruptured at the Philadelphia Energy Solution's refinery, Pennsylvania, USA. A large vapor cloud engulfed part of the unit and ignited causing large explosion and fire. U.S. Chemical Safety and Hazard Investigation Board (CSB) conducted an incident investigation and issued the final report on October 11, 2022. The cause of the incident was that the carbon steel piping elbow of the alkylation unit with high nickel and copper content had corroded and thinned faster than adjacent piping components with lower nickel and copper content. The ruptured elbow released propane and toxic hydrofluoric acid to the atmosphere. This paper describes the incident based on the CSB report.

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