Fitness-for-Service

In a fitness-for-service (FFS) assessment of a welded pressure-bearing structure, there is a class of stress that comes neither from external load nor from a residual field, but from imperfect fabrication and fit-up — the weld joint is “not aligned”. BS 7910:2019 Annex D handles exactly this: when two plates or shells to be welded together have axial misalignment or angular distortion, the load path of a tensile load is forced to bend, and a layer of local bending stress $\sigma_s$ appears at the weld. ...

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.” ...