As an alternative method to evaluation of slow strain rate technique (SSRT) under high-pressure hydrogen gas, SSRT tests were performed with a ca-thodically charged specimen. Cathodic charging was performed in 3% NaCl aqueous solution with pH＝6 and at a current density of 50 and 400 A/m2. Cr-Mo low alloy steel with a tensile strength of 1000 MPa grade was selected as a test material. Relative reduction of area (RRA) values obtained by tests with continuous charge at a cathode current density of 400 A/m2 were equivalent to those performed in hydrogen gas at pressure of 35 to 115 MPa. Fracture surface observations were also performed using scan-ning electron microscopy (SEM). The quasi-cleavage fracture surface of hy-drogen embrittlement (QCHE) was observed near the surface of specimen subjected to continuously hydrogen charged tests. QCHE rate on fracture sur-face increased with increasing cathodic current density and decreasing diam-eter of specimen. RRA decreased with increasing of the QCHE rate, reached the minimum value of RRA＝0.4 with the QCHE rate about 40%.
Recently, a technique has been developed to render harmless surface cracks which reduce the fatigue limit of metals by 20～60% by the effects of compres-sive residual stress induced by shot peening. This technique is called as sur-face crack non-damaging technology. For the purpose of contributing to reliability improvement of high strength steel equipment by surface crack non-damaging technology, the following research was carried out: (a) The effects of aspect ratio of surface crack on maximum harmless crack depth (ahlm) of a high strength was calculated for three residual stress distributions. (b) Assuming the value of safety factor, the relationship between the maximum allowable crack depth (acrN) and ahlm was investigated. (c) The relationship between maximum detectable crack depth by non-destructive inspection (aNDI) and ahlm was compared, assuming that nondestructive inspection could detect the crack with sufficient probability. (d) The relationship between ahlm, aNDI and ahlm were compared.
On October 31, 2016, a 36-inch buried gasoline pipeline of Colonial Pipe-line Company exploded in a forest area near Helena, Alabama, USA. The Na-tional Transportation Safety Board（NTSB) which conducted the investigation published the report on December 10, 2019. The NTSB determined that the probable cause of the explosion was the excavation crew's inade-quate planning, coordination, and communication during the excavation. This paper describes the accident based on the NTSB report.