A batch of high-strength bolts is installed and torqued on Friday. On Monday, three heads are on the floor. Nothing hit them; nothing changed. This signature — brittle fracture, delayed by hours or days, in a normally tough material under static load — is hydrogen embrittlement, and it is one of the most commercially contested failure modes we see, because it almost always points at a processing step.
How hydrogen breaks steel
Atomic hydrogen is small enough to diffuse through the steel lattice. Under stress it accumulates at the points of highest tension — thread roots, crack tips, inclusions — where it lowers the material's resistance to cracking. The result is fracture at loads the material should shrug off, with the delay explained by the time hydrogen needs to diffuse to the critical spot. Susceptibility rises sharply with strength: the harder the steel, the less hydrogen it takes.
Where the hydrogen comes from
- Electroplating and pickling. Zinc and cadmium plating charges hydrogen into the steel; that is why plated high-strength fasteners must be baked promptly after plating to drive it out — and why a skipped or late bake is the classic root cause.
- Welding. Moisture in consumables or on the joint dissociates in the arc; hydrogen cracking appears in the weld or heat-affected zone hours to days later — the reason low-hydrogen electrodes, baking and preheat exist.
- Cathodic protection and service environments. Over-protected subsea bolting and sour (H₂S) service both charge hydrogen in operation — a design/compatibility question rather than a processing one.
What the investigation looks for
- Fractography. Brittle, typically intergranular fracture near the initiation region in a material that should fail with dimpled ductility — with little or no deformation.
- Timing. Delayed, static-load fracture is highly characteristic; it separates hydrogen from simple overload immediately.
- Hardness and microstructure. Was the component at the strength level where embrittlement is credible — and was it heat treated as specified?
- Processing history. Plating records, bake times and temperatures, welding procedures — the paper trail usually decides where the hydrogen entered.
The near relatives matter too: stress-corrosion cracking (compared here) and corrosion fatigue can imitate aspects of hydrogen damage, and the corrective actions differ. That is why the mechanism must be confirmed, not assumed.
Why it is commercially loaded
A confirmed hydrogen-embrittlement verdict on plated fasteners typically implicates a processing step — which makes it a supplier-quality question with warranty consequences. Independent, evidence-led confirmation protects both sides of that conversation. Bolting failures more broadly →
When to contact MTIS
Unexplained brittle fractures of high-strength components — especially delayed ones, especially in batches — deserve investigation before the remaining stock is used. Keep the broken pieces and a sample of unused items from the same batch, and request an investigation. Related: supplier-quality investigations →