Fasteners are the smallest components on an asset and among the most consequential: one failed stud on a pressurised flange is a leak, a fire case, or a dropped load. They are also uniquely informative failures — a bolt is a simple, well-defined test specimen that was working until it wasn't.
The four usual suspects
- Fatigue. The classic signature: fracture in the first engaged thread or under the head, beach marks radiating from the thread root. The root cause is almost always lost preload — a properly tensioned bolt sees very little of the joint's load cycling; a loose one sees all of it. Fatigue signatures →
- Hydrogen embrittlement. Brittle, delayed fracture of high-strength (typically plated) fasteners, often in batches, days after torquing. Points at plating and baking practice. Full explainer →
- Overload. Necked, ductile fracture from over-torquing or an event; or thread stripping where engagement or property class was wrong. The geometry usually says which.
- Corrosion-driven failures. Crevice attack under heads and in threads, galvanic attack from mixed metals, and SCC of susceptible high-strength grades in specific environments — including over-protected subsea bolting.
The batch question
One broken bolt is a component question; three from the same carton are a batch question. Wrong material, wrong heat treatment, skipped bake, mis-marked property class — batch problems have a way of announcing themselves gradually, and the right response to the first delayed fracture is to quarantine the batch and test samples, not to replace one bolt and hope. Material verification and hardness on unused fasteners from the same batch is quick and decisive.
What to keep when a bolt fails
- All pieces of the failed fastener(s), fracture faces protected and uncleaned.
- Unused fasteners from the same batch/carton — the investigator's control sample.
- The nut, washer and mating parts.
- Torque/tensioning records and the joint's service history.
- Markings: head stamps and property-class marks, photographed before anything else.
Why these investigations are commercially loaded
A fastener verdict usually assigns the problem to one of three parties: the manufacturer (material, processing), the installer (preload, torque), or the operator (environment, load). Getting the mechanism right — with evidence — is what keeps that conversation factual. Supplier-quality investigations →
When to contact MTIS
For any fastener failure on safety-critical or pressurised equipment; for delayed or multiple failures from one batch; or when a warranty conversation needs independent facts. Request a project quote →