In-Service Refinery and Pipeline Cracking Initiated by Hydrostatically Induced Strain

A new phenomenon of in-service cracking has been observed in carbon steel pipelines, refinery piping and refinery equipment that is initiated by sources such as hydrostatic testing and is identified as Strain Accrual Hydrogen Cracking. Although hydrostatic testing is beneficial to blunting crack tips and reducing crack propagation, high hydrostatic test pressures approaching yield cause localized threshold strains in weldments and base materials that consequently increases the susceptibility to nascent hydrogen embrittlement at strain boundaries. This paper discusses strain accrual hydrogen cracking mechanisms, beneficial and detrimental effects of high hydrostatic test pressures, increased Code allowable stresses, micro alloying additions and strain based design, case histories, and suggests mitigation practices.