Why a fastener can fail after assembly

Hydrogen embrittlement can cause brittle fracture in susceptible steel fasteners under tensile stress. Failure may be delayed rather than occurring during tightening. Fraunhofer IWM identifies dissolved atomic hydrogen as a cause and distinguishes hydrogen-related cracking from fatigue and overload failures. A broken bolt therefore needs investigation; its appearance or the time of failure alone should not become a diagnosis.

For a buyer, the practical implication is to review the process before production. Waiting for an assembly trial to reveal every risk is a weak acceptance strategy. Keep the drawing, specification revision and supplier response together so that the engineering decision can be reconstructed later.

Sources: Fraunhofer IWM: Hydrogen-induced fractures in bolts and bolted joints

Review material condition alongside the finish

Wurth Industrie Service highlights hydrogen embrittlement risk in high-strength bolts and notes that hardness can matter locally as well as across a component. Its guidance also states that risk-reduction processes cannot guarantee complete elimination, particularly when service conditions such as corrosion contribute. Avoid treating a property-class label as a complete risk assessment.

As a purchasing recommendation, request the specified material condition and any relevant hardness requirements in the quotation package. Ask the responsible engineer to identify which drawing requirements govern the decision. When comparing suppliers, use the same revision and the same acceptance questions; otherwise, similar prices may represent different assumptions.

• Identify the material specification, heat-treatment condition and drawing revision.
• Ask which finishing and pretreatment steps the supplier proposes.
• Resolve differences between the drawing, purchase order and supplier quotation before production.

Sources: Wurth Industrie Service: Hydrogen embrittlement

Ask about the full manufacturing route

Fraunhofer IWM lists electrolytic processes, upstream pickling and corrosion among possible hydrogen sources. It describes process measures that reduce hydrogen entry and suitable heat treatment that can remove dissolved hydrogen. These are process-dependent measures, not a universal recipe for every steel fastener.

For an RFQ, ask the supplier to describe the proposed route rather than supplying only a coating trade name. Request an explanation of how the route addresses the material and the specified application. If a relief treatment is required, have the responsible engineering authority approve its parameters and records. This guide does not prescribe a temperature, duration or processing delay.

• Include cleaning, pretreatment, coating and any specified relief treatment in the review.
• Ask how outsourced operations will be identified in the production records.
• Require approval of a proposed process change before it is used on the order.

Sources: Fraunhofer IWM: Hydrogen-induced fractures in bolts and bolted joints

Separate appearance checks from acceptance evidence

Bossard explains that hydrogen-related fastener failures may emerge hours, days or weeks after assembly and can be difficult to detect in routine production or outgoing inspection. A visually clean coating should therefore not be presented as proof that a fastener is free of this risk.

Our recommended buyer checklist separates three questions: Does the part match the drawing? Was the agreed manufacturing route followed? What evidence supports acceptance for this order? Ask for the required records by name, including who reviews them and when they must be delivered. Do not accept an undefined promise to provide a certificate later as a substitute for an agreed acceptance plan.

• List the inspection and process records required with the shipment.
• Agree on the applicable test requirements and acceptance criteria with qualified engineering personnel.
• Define what happens when records are missing or results do not meet the purchase requirements.

Sources: Bossard: Hydrogen Embrittlement of Fasteners

Include service conditions in the purchasing discussion

Manufacturing controls are only part of the discussion. Wurth's guidance specifically identifies service influences such as corrosion as a reason why complete risk elimination cannot be guaranteed. An application review should therefore explain the intended environment instead of relying solely on a general statement about the finish.

As a practical RFQ format, provide a short application description, the controlled drawing and a list of open engineering questions. Ask the supplier to respond to each question explicitly. Mark a proposed substitution as pending until it has been approved. This makes the handoff between purchasing, quality and engineering clearer without assuming that every organization uses the same internal workflow.

• Describe the intended exposure and any relevant customer requirements.
• Identify the person or team authorized to approve material and finish substitutions.
• Keep unresolved application questions out of the released production specification.

Sources: Wurth Industrie Service: Hydrogen embrittlement

Build a clear RFQ for Chuanghe Fasteners

When discussing a custom fastener order with Chuanghe Fasteners, submit the current drawing, material and finish requirements, expected quantity and required acceptance documentation. Ask for confirmation of the proposed scope and identify any exceptions before placing the order. This is a suggested purchasing checklist; it does not establish a particular coating, test method or certification as a confirmed factory capability.

Use the related surface-treatment guide as background for the specification discussion. Keep the final order requirements specific to the component and its application. A useful supplier response states what is included, which questions remain open and what approval is needed before manufacture. The goal is an auditable agreement, rather than a broad claim that a process makes hydrogen embrittlement impossible.

Sources: Bossard: Hydrogen Embrittlement of Fasteners