FAD

In a BS 7910 fracture assessment most attention goes to flaw size, stress and toughness — but one thing hidden in the material is easy to miss: when this steel yields, does it pass smoothly into plasticity, or does it “catch, then let go” first? This small metallurgical detail grows a cliff in the failure assessment line near $L_r=1$ — get it wrong and you badly overestimate the safety margin. This article explains what yielding is, how continuous and discontinuous yielding differ, and how Option 1 and Option 2 each handle them. ...

In a BS 7910 fracture assessment, the horizontal axis $L_r$, the vertical axis $K_r$, and the failure assessment line (FAL) that separates “safe” from “unsafe” — how the assessment point is computed and how the verdict is read — are covered thoroughly in the BS 7910 Fracture Assessment — A Concise Guide . This article covers one thing only: Clause 7 gives three ways to draw that FAL curve (Option 1 / 2 / 3). They step up in the material data they need, in computational accuracy and in conservatism; understanding their differences is a key step to doing a fracture assessment “correctly and economically”. ...

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 second worked example in the [[FITNET|FITNET]] FAD example collection (§13.2.6, SSTP10). Its focus differs from the [[bs7910-a533b-residual-stress-fad|first A533B example]]: this time it is a welded stainless-steel wide plate with a through-thickness crack, assessed for ductile tearing (the crack grows stably as the load rises) on the FAD. We follow the [[bs7910-a533b-residual-kis-annexm|usual routine]] — run it in mechCalc’s BS 7910 Clause 7 fracture assessment calculator, read the chart, and cross-check point by point against the FITNET literature. ...

This is the finale of the four problems on the A533B-1 welded plate. It is the counterpart to Problem 3, [[bs7910-a533b-hlaw-fad-walkthrough|HLAW]], and it pushes the power of PWHT in this test series into its most visible form. The shared background and method for all four problems are covered in the overview, [[bs7910-a533b-residual-stress-fad|Where does residual stress push the assessment point?]]. What this problem asks HLHT = High-$L_r$ + Heat-Treated: PWHT applied, assessment temperature −30 ℃, high load ratio. It shares the temperature and regime of HLAW, and the difference is still that one thing — post-weld heat treatment. But at −30 ℃, PWHT delivers a double dividend: ...

This is the third of four problems on the welded A533B-1 plate. The first two both sat in the low load-ratio brittle-fracture regime and compared residual stress; this one shifts the battlefield — to the high load-ratio, large-plasticity regime. For the shared background and method behind all four problems, see the overview post [[bs7910-a533b-residual-stress-fad|Where does residual stress push the assessment point?]]. What this problem asks HLAW = High-$L_r$ + as-Welded: as-welded condition, assessment temperature raised to −30 ℃, load increased into the high load-ratio regime. The warmer temperature lifts the fracture toughness somewhat off the lower shelf ($K_{mat}=62\ \mathrm{MPa\cdot m^{0.5}}$), while the load is raised to a failure load of 5.10 MN. The residual stress stays the as-welded value ($K_I^S=46$). ...

This is the second of the four problems on the A533B-1 welded plate, and the companion to Problem 1 [[bs7910-a533b-llaw-fad-walkthrough|LLAW]]. The two problems were designed for a single-variable comparison: The shared background and method for all four problems are in the overview [[bs7910-a533b-residual-stress-fad|Where do residual stresses push the assessment point?]]. What this problem asks LLHT = Low-$L_r$ + Heat-Treated: post-weld heat treatment (PWHT) applied, assessment temperature −120 ℃, low load ratio. It is at the same temperature as LLAW, in the same region, and uses the same set of measured residual-stress profiles — the only variable is PWHT. The heat treatment relaxes the welding residual stress by at least an order of magnitude, so the residual $K_I^S$ drops from 46 in the as-welded state to 5 MPa·m$^{0.5}$. The load capacity rises accordingly, from LLAW’s 1.27 MN to 2.19 MN (about 1.7×). ...

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? ...