Fracture Mechanics

This is the first of four problems on the A533B-1 welded plate. The shared background, common method, and residual-stress profile for all four are set out in the overview post: For the overview and method, see [[bs7910-a533b-residual-stress-fad|Where does residual stress push the assessment point? — A FAD recomputation of the A533B-1 large welded-plate fracture tests]]. This post focuses on one specimen and walks it through the calculator from input to reading the chart. ...

In the fracture-mechanics and fitness-for-service (FFS) literature, FITNET is a name you cannot avoid. Many large-component fracture-test examples, and many assessment results cited for cross-checking, are marked “from FITNET”. What is it, where did it come from, and why is it authoritative? This article sets it out from public sources. 1. In one line: what FITNET is FITNET (European Fitness-for-Service Network) is an EU-funded research collaboration network. Its goal is one sentence: to establish a unified, validated fitness-for-service procedure for flawed metal structures (welded and non-welded) — the later FITNET FFS Procedure. ...

When you run a fitness-for-service (FFS) assessment on a welded pressure component, welding residual stress is almost always one of the hurdles you cannot step around. It is a textbook secondary stress (a self-balancing field): it plays no part in static equilibrium, yet it genuinely raises the driving force at the crack tip. The question engineers have asked for years is this: on the Failure Assessment Diagram (FAD), where does residual stress actually push the assessment point — and how much can post-weld heat treatment (PWHT) pull it back? ...

Pressure vessels, pipelines, and structures develop flaws during service — cracks, corrosion, wall thinning. When an inspection finds such a flaw, engineers face one key question: Can this equipment keep running? If so, for how long? This is exactly what Fitness-for-Service (FFS) assessment answers. The Limit of Traditional Rules Traditional design codes (such as ASME or GB 150) are written for new, flaw-free equipment. When a flaw is found, the codes often say: “out of tolerance — repair or retire.” ...

The fracture assessment of a cracked structure watches two competing failure modes. This guide uses a single Failure Assessment Diagram (FAD) to weave together the assessment principle, the calculation chain, and the BS 7910 assessment steps into one clear storyline. By the end you should be able to see how an assessment point is computed and how it is judged acceptable or not. Prologue: after a crack is found When an in-service pressure vessel, pipe, or welded structure is inspected, crack-like flaws are often found. The question the engineer must answer is not “can this crack be used” — a crack is not something you “use” — but rather: can the structure that contains this flaw still operate safely under the current loads? ...

This article explains how to use the seven-step method of the KTA 3206 standard for a Leak-Before-Break (LBB) analysis of nuclear piping. It pairs with the KTA 3206 LBB Pipe Analysis module of the online calculator, taking you from theory to practice. 🧮 Try the calculator now: open the KTA 3206 LBB pipe analysis calculator , choose “Fracture Mechanics → KTA 3206 LBB Pipe Analysis”, and enter the parameters to get results with a detailed formula derivation and visual charts. ...

This is a detailed introductory guide to Leak-Before-Break (LBB). LBB is a crucial safety concept in the structural integrity assessment of pressure vessels and piping. In short, it is an analysis that proves the equipment will produce a detectable leak first, before any catastrophic fracture — giving operators time to shut down and avoid a major accident. 1. What is Leak-Before-Break (LBB)? Core definition: LBB is a property of a pressure-bearing system (pipe, vessel). It ensures that when a flaw (crack) is present, the crack will penetrate the wall to form a through-wall crack and produce a stable, detectable leak before it grows to the critical size that would cause overall structural instability (sudden fracture or plastic collapse). ...