What is a Mill Test Report (MTR) and Why is it Important?

January 8, 2015
Typical Markings on an ASME BPE Sanitary Fitting. The 835877 Number is the Heat Number

Typical Markings on an ASME BPE Sanitary Fitting. The 835877 Number is the Heat Number

At Holland, we understand the importance of quality assurance. Whether we’re manufacturing a vessel or an adapter, using the assurance that you’re using the material you think you’re using is critical. While previous posts have focused on the importance of PMI for quality assurance, in this post we’re going to take a closer look at what a mill test report is, what information they provide, and why they are so important in the high purity processing industry.

To begin, a Mill Test Report (MTR) in the world of sanitary process is a quality assurance document that records the chemical and physical properties of the stainless steel (or other alloys) used in the fabrication of hygienic process components and equipment. MTRs go by a variety of names, including Certified Mill Test Report (CMTR), Mill Certification, or Metallurgical Test Report. When a heat (lot) of steel is generated at the mill, it is assayed.  The results of that assay are recorded and an MTR is generated.  Whether the lot of steel is then processed into plate used to manufacture vessels, strip used to make fittings and tubing, or larger shapes to be used in machining valves or pumps, that heat number and its accompanying MTR are tracked throughout the manufacturing process.

Finished products normally have the heat number (or numbers) stamped onto the outside surface to maintain the traceability of the part. This process is followed for all 316L stainless material and higher grade alloys.  Normally the heat numbers of 304 stainless steel are not tracked.  At Holland, it is our receiving and quality control groups’ responsibility to inspect and match received goods to their corresponding MTR to ensure that the components received meet the purchase specifications.

To begin understanding the information that an MTR provides, we need to start by understanding how material is labeled for identification. There are a variety of ways that material manufacturers can do this, but they all usually loop back to a Heat Number. When matching an MTR to its raw material, all accompanying paper work, and in most cases markings on the part itself, must match the heat number on the MTR.

So now that we know how to match a part with its MTR, what information does it provide other than the basic material type? First, the MTR provides the specific material grade of a material (316 or 316L). The MTR will also certify that parts meet appropriate ASTM and ASME specifications. Compliance with ASME guidelines is especially important when fabrication pressure vessels that are to receive an ASME stamp.

The MTR will also identify the dimensions of the raw material. For most fittings, this is the tube or bar stock thickness and width. While this information is important, the part that most stands out are the actual measured properties for the material. In order to comply with the material the cert says it is, these properties must fall within the range limits of that materials specification. The carbon, sulfur, chromium, and nickel contents of the material are all listed in this section. This detail is similar to what our x-ray fluorescence analyzer spits out when we zap a piece of steel that isn’t properly marked. Finally, the MTR is certified with the signature of a responsible employee of the foundry or mill producing the raw material.

At Holland, we maintain MTR records of virtually every piece of traceable material that we supply.  If you need more help understanding what’s on your MTR, or even retrieving the MTRs from a component you purchased previously, contact a Holland Sales Engineer today.