When it comes to sourcing stainless steel, titanium, or nickel alloys, it is only half the battle. For procurement and engineering professionals in the aerospace, marine, chemical processing, and power generation industries, the metal is often secondary to the value of the paperwork that accompanies the delivery. That paperwork is generally in the format of a mill test certificate (MTC) and understanding the importance of the MTC is often an unappreciated aspect of industrial purchasing.
A mill test certificate (MTC) is a document from the steel or alloy manufacturer that verifies the chemical composition and the physical properties of a specific lot. In Europe, and the UK, mill test certificates fall under the EN 10204 classification system, with the 3.1 certificate being the most frequently requested. A 3.1 certificate is one in which the manufacturer’s quality department (outside of the production department) prepares the certificate and it attests that the material is in conformance to the order.
In the aerospace and defence sectors, where components must adhere to strict and specific requirements, a 3.1 certificate is considered substandard. In fact, a 3.2 certificate is often required, which means that the certificate is the product of validation from an independent third-party inspector rather than the manufacturer. Ordering the wrong certificate can result in upstream delays of weeks as process material is re-ordered along with the required certificates.
The importance of traceability becomes clearer when it comes to less apparently regulated industries. An example is chemical processing; the wrong grade of stainless steel on a pipework installation will not only cause costly downtime but may also cause a safety incident. In marine and offshore environments, the use of certain corrosion resistant nickel alloys is mandatory because an untested or wrongly substituted batch of materials would make the design useless. While some facilities managers and purchasers may ask for complete certification, they are not being overly conservative. They are trying to ensure the integrity of the asset being constructed.
What should purchasers look for in order to sign off a delivery? Check that the heat or batch number matches the number that is either stamped or labelled on the material. Review the chemical composition against the pertinent standard, whether that is an ASTM, EN, or AMS specification. Also check the mechanical tests (tensile strength, yield strength, and elongation) that are applicable to the particular use case. For titanium and nickel alloys that are used in aerospace or marine fixtures, make sure the certificate cites the correct specification revision to avoid confusion during audits since specifications are subject to periodic updates.
It’s also worthwhile when developing supplier relationships in a way that makes traceability less of an afterthought. A supplier who can quickly provide full certification history for a batch and who knows the difference between a 2.2, 3.1, and 3.2 certificate saves procurement teams a great deal of work during compliance audits. This is especially true for organisations with quality standards such as AS9100 in aerospace, or ISO 9001 in other industries, because the auditing process requires documented material traceability within the audit trail.
The certificate is more than an administrative task to complete. It shows that the stainless steel, titanium, nickel alloy, or aluminium that your organisation is receiving is suitable for the intended application, whether that be a chemical processing vessel, a power generation feed water heater, or an aerospace component. Rather than considering this paperwork to be a task that needs to be completed, the time spent on understanding and validating the documentation is a small cost to further safety and the reputation of the organisation down the supply chain.
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