Papers by Author: M. Law

Abstract: Miniature specimen testing to evaluate mechanical properties, presents a novel opportunity to undertake structural integrity assessments of in-service power generation components, by removing only a very small volume of material. In this study, high temperature fatigue testing of P22 steel was undertaken and a number of fatigue properties determined using a miniature specimen testing methodology. Good comparisons were observed between fatigue properties determined by miniature specimens and the more established standard-sized specimen testing reported in literature.

Abstract: Hydrogen cracking in steel weldments can drastically reduce the toughness and ductility of welds in steel structures. Unfortunately, the development of the hydrogen economy will also see materials being increasingly exposed to hydrogen, in processes such as during hydrogen production and transportation. Thus, test methods are required which allow for a reproducible assessment of hydrogen embrittlement in weld material. In this article, rectangular test specimens made from weld bead on plate samples were subject to 4-point bend testing to investigate the relationship between applied stress, hydrogen content and embrittlement. This test concentrates the stresses in the weld bead, thus reducing the effects of premature HAZ cracking and enabling failure to develop in the weld metal, and showed good reproducibility. This test may form the basis for an industry test. Another test method is described using an un-machined weld bead on plate. A method of calculating the stresses and strains in this specimen in 4-point bending was developed.

Abstract: A section of gas pipeline containing dormant stress corrosion cracks was removed from service and pressure cycled, and the crack growth from fatigue was measured. Crack growth was able to be conservatively calculated by BS7910. Parts of the pipeline section had composite repair sleeves placed over it in order to compare fatigue crack growth of sleeved and unsleeved cracks. Sleeved cracks consistently showed less crack growth than unsleeved cracks; this is believed to be due to reduced hoop stresses in the pipe under the composite repair sleeve and reduced crack opening. A simple model of the sleeve repair was developed which was consistent with the measured strains in the pipe. The application pressure of the sleeve repair affects the amount of stress reduction in the pipe and the amount of crack growth experienced. Two possible methods of repair of SCC affected pipelines were validated by this work.