A Mill Test Certificate (MTC) or a Mill Test Report (MTR) is an important component in the transaction between the manufacturer and buyer of steel products such as plates, bars and strips. The MTC will include all specifications of the steel product, including dimensions, sizes, weight, chemical composition, mechanical strength, heat treatment status, test results, traceability, and so on. As the steel is processed into a finished product (vessels, pipe, fittings, couplings, etc.), there may be need to track it to the original MTC, in order to fulfill traceability requirements. One standard often referenced as guidance for such requirements is the EN 10204.
The EN 10204 is the European standard for the inspection documents of steel products, including steel couplings, line pipes, fittings, and sucker rods. This article will focus on the EN 10204 standard and explore its importance for steel coupling products.
By Davi Correia, Senior Mechanical Engineer
The Correct Level of Inspection
Imagine a designer is doing the final verification for a new product. Once the numbers have been deemed satisfactory, the manufacturing process may begin as soon as the necessary materials are procured. The purchasing team is to acquire the materials, with the correct properties, that match those used by the designer in their calculations.
Ideally, the manufacturer would simply need to reach out to a supplier and ask for the required standard and grade of material. It is not, however, that simple. It is crucial to ensure that the chemical composition and mechanical properties stated on paper are identical to their physical counterparts, which adds further costs to the project. If the design in consideration is for a garden hose or a standard American Society of Mechanical Engineers (ASME) pressure vessel, the general consensus is to not pay for the same level of assurance, although, both products are bound to hold pressure. The level of inspection and traceability needs to be determined and agreed upon for each product.
Inspection, Traceability, and the EN 10204
There is an old saying: “You do not get what you expect, you get what you inspect.” The decision of how much inspection and traceability is required for a specific product is determined mostly by standards, national and international regulations, the level of confidence, and economic factors.
As the topic of inspection is vast, it is crucial to shed more light, and look at the common standards used worldwide to define the inspection or certification documents that help attain traceability. The EN 10204 ‘Metallic products – Types of inspection documents’ (October 2004) originated with a German standard (DIN 50049), and covers both metallic and non-metallic materials. The EN 10204 defines four levels of documentation, which can be seen in Table 1.
When Type 2 documentation (2.1 and 2.2) is chosen, the end user relies solely on the manufacturer’s quality control capabilities to deliver the properties and composition needed. Type 2.1 provides a statement that indicates that all is well. Type 2.2 provides the same statement, but with the addition of test results that have not necessarily been taken from the samples collected in the batch/run/heat being purchased. EN 10204 calls this a ‘non-specific’ inspection.
Types 3.1 and 3.2 provide results from a specific inspection, that is, on the products to be supplied or on test units of the products being supplied. For Type 3.1, the manufacturer’s representative is involved; he or she must be independent of the manufacturing department. For Type 3.2, the manufacturer sends a similar representative, who must liaise with either the purchaser’s representative or an inspector designated by the official regulations. It is clear that certificates Type 3.1 and 3.2 are generally much more expensive than Type 2.1 or 2.2. It is also worth calling attention to the fact that Type 3.2 interrupts the normal flow of the production line. A stop sign is placed on the specified product until the day of the witnessed tests and inspection.
The EN 10204 does not state which tests must be performed on each product, nor does it give advice of which is the correct documentation to select; this is the purchaser’s job. The purchaser must perform this analysis beforehand, and provide the supplier with the results. The EN 10204 does define, in a simple manner, the required inspection documents and level of witnessing.
It is important to recognize that there are some issues and misconceptions regarding the EN 10204. For example, it is the belief that the EN 10204 Type 3.2 certification requires a batch/run/heat number to be stamped on the final product. This is not necessarily true. The only reference to required markings is in Item 6 (transmission of inspection documents by an intermediary). Here the standard states: “An intermediary shall only pass on either an original or a copy of the inspection documents provided by the manufacturer without any alteration. This documentation shall be accompanied by suitable means of identification of the product, in order to ensure traceability between the product and the documentation.” Therefore, what is ‘suitable’ must be defined in the fabrication standard or the purchase order. Bolts are a good example of this. As per the American Society for Testing and Materials (ASTM) A193, a B7 bolt must be marked only with grade type and manufacturer. The purchaser can further define in the purchase order that the heat number must be marked as well, see Figure 1.
Buying Products from Stockists/Stockholders
The EN 10204 differentiates between manufacturers and stockists/stockholders. The differences are referred to as intermediary in the standard and the definitions are as follows:
An organization that manufactures the respective products according to the requirements of the order and to the properties specified in the referenced product specification.
An organization which is supplied with products by the manufacturers and which then in turn supplies them without further processing or after processing without changing the properties specified in the purchase order and referenced product specification.
For example, a stockist that only cuts or saws a bar is to be considered an intermediary. An intermediary cannot issue certificates as per EN 10204. It can only forward the certificates it already has for products in stock (as seen on Item 6, described previously).
There are times, however, when the project requires Type 3.2 certification and the purchaser must buy the materials for a stockist. In this case, a sample can be re-tested with third party witnesses, and certification can be issued as to the ‘intent’ of Type 3.2 by the intermediary. Note that this is not a true Type 3.2 as per EN 10204, and therefore, this type of procedure must be agreed upon between buyer and supplier.
EN 10204 for Hoses and Couplings
The original intention of the EN 10204 was for it to be applied to raw materials. Since its inception it has become increasingly common to see finished products like industrial hoses require EN 10204 certification, frequently using a combination of types for various parts. For example, Type 3.1 has been required for the metallic pressure-containing parts, and Type 2.1 has been required for the non-metallic parts.
In this case, the supplier must present a Type 3.1 certificate for the fitting or coupling, and a Type 2.1 certificate for the packing. As this falls outside the original scope of the standard, it is a good practice to have absolute clarification with what the purchaser requires.
If this clarification is not given, a situation may arise where, as a manufacturer, the hose assembler interprets that simply performing the pressure tests with the required witness is sufficient to issue even a Type 3.2 certificate for the assembly.
Other possible point of contention is the marking of small parts. There must be absolute certainty about what information must be marked according to each diameter. Figure 2 depicts an example of the marking.
The world of manufacturing today can often rely on complex supply chains. The more complex the supply chain, the harder it can be to clarify for all the involved parts the specifications needed by the end user.
The EN 10204 is available to help alleviate some of the burden, although in the end, the surest way to reduce surprises is to have a strong relationship with the suppliers. When we add the pages of some product specifications, they can easily pass for a little book (a chapter for materials, another for fabrication, painting, etc.).
Only a supplier who is motivated for the long run can be expected to read this ‘book’ thoroughly and clear all the doubts beforehand. In doing so, it allows for the ability to deliver the products that meet the end user’s necessities.