MTR: Mill Test Reports

Each day, we take for granted that the metals we encounter and use in our ordinary lives are safe. The steel framing in apartments and high-rise buildings, the aluminum fuselage of a passenger plane, the metal making up our cars and appliances: very rarely do we question the composition of the metal itself. Our lives go smoothly because we can trust these metals are safe and sturdy. We’re able to make that assumption because of the quality controls practiced by the metal industry, and that quality assurance rests largely on the mill test report (MTR).
At every step of the manufacturing process, the metal is accompanied by its MTR. From the mill forging the material, to the service center performing heat processing and finishing, to the company purchasing the items, the MTR passes from hand to hand. But what exactly is included in a mill report that makes it so important?

Mill Test Report
¬As might be expected, most mills will have their own style and layout for an MTR. They may not even call it a Mill Test Report at all: MTR is industry jargon that can also refer to a Material Test Report, a Mill Certification, or Mill Inspection Certificate. But whatever the name, the information the MTR includes is standard across the industry. When reviewing the document, you can expect it to list the following:

• Production information: the metal’s country of origin, melt location, and manufacturer’s name

• Product description: the item’s alloy, temper, grade, finish, width, thickness, and weight

• Material heat number: also referred to as the heat lot, this is an identifying code that is stamped directly onto the metal itself. As each lot of metal is produced, it is assigned a unique code to identify it as part of that batch. This provides a high degree of traceability, no matter where the metal might end up or its purpose. If there is any type of recall or issue with the metal, this number allows it to be traced back to its origin.

• Mechanical and physical properties: this states the metal is compliant with the criteria set by an international standards organization, such as ASME or ANSI. It is especially important in the case of alloys, because it certifies the chemical makeup of the metal. This is where the “test” portion of the MTR applies. While the metal is molten, a sample is drawn from each batch for metallurgical chemical analysis. Once the item is forged, mechanical testing is then performed on the finished item. Putting items such as steel plate through hardness, tensile and impact tests establish that the material will perform to the necessary standards under specific conditions.

• Inspection: in addition to the mill’s test information, the metal requires certification from an independent inspector. This means the MTR typically includes two signatures verifying the material’s makeup: one from the mill itself while producing the metal, and a second from the inspection agency. This third party inspection provides additional authentication of the metal’s physical and mechanical properties, along with confirmation that the heat number matches the actual item. If all information is correct, the inspector signs off on the report as a final step.

Do I Need the MTR?
For companies involved in the industrial side of manufacturing, distribution, and use of metals, MTRs are a necessity. These standards ensure that the metals will be appropriate for their intended use, and able to measure up successfully to further processing such as welding with compatible metals. If the finished goods or structures later experience some type of metal failure, the information provided by the MTR enables every item can be traced back to its source.
However, MTRs aren’t a necessity for the average consumer. Buying from reputable mills and distributors means that they have done the groundwork for you by collecting the MTRs for their products. Companies are required to keep their MTR documentation for a minimum of three years. However, many companies keep their records for much longer, priding themselves on being able to trace back their materials whenever the occasion may arise.