BS 7910 Annex M: Analytical Calculation of the Stress Intensity Factor (K_I) — Theory and Practice
In the structural integrity assessment of pressure vessels, oil and gas pipelines, offshore steel structures and nuclear pressure-boundary components, the stress intensity factor (SIF, written $K_I$) is the central quantity of Linear Elastic Fracture Mechanics (LEFM). It measures precisely how strong the singular stress field is at the crack tip. The flaw assessment standard BS 7910:2019+A1:2020, published by The Welding Institute (TWI), sets out in its Annex M a classic, high-accuracy and self-consistent system of analytical SIF solutions for the eight common geometry groups met in engineering. This article explains its physical basis, the code calculation chain and its engineering use, and introduces an interactive online calculator built entirely in pure Python. ...