REQUESTING THE APPROPRIATE LEVEL OF WELD TESTING FOR SPECIAL ORDER FILLER MATERIALS
Welding filler metal certification, documentation and accountability is frequently a step of the nuclear pressure vessel fabrication and military shipbuilding process. Here is how to select the appropriate weld testing requirements to verify quality and attest that the products being supplied meet the constituents of the required specification.
Welding filler metal certification, documentation and accountability is frequently required by companies working on critical applications in sectors such as nuclear pressure vessel fabrication and military shipbuilding. For many of these applications, the filler metal manufacturer is requested to conduct welding tests on a representative sample of the product lot to verify quality and attest that the products being supplied meet the constituents of the required specification.
In this installment of the Welding Tips column, I will discuss the process of selecting the appropriate weld testing requirements in the vernacular of the American Welding Society (AWS; Miami, FL) A5.01 Filler Metal Procurement Guidelines.
Before launching into a discussion of the appropriate level of weld testing when purchasing special order welding consumables, the first order of business is to clear up a common misconception regarding filler metal certificates or “certs”. It cannot be stressed enough that what fabricators actually want is a certified material test report (CMTR) from the filler metal manufacturer rather than a “mill cert” when ordering tested welding consumables.
A mill cert is nothing more than an analysis of the heat of steel conducted at the mill where the “green rod” (or strip coil for some filler metal products) was produced. While this gives us a ballpark idea regarding the chemistry of what will end up in the weld metal deposit, it does not tell the full story.
The first reason that a mill cert does not tell the full story is that it reports only an average of the chemistry measured just a handful of times in a ladle pour of approximately 300,000 lb. Some manufacturers of welding consumables, including my company, measure both ends of each 1,000 lb to 5,000 lb coil of steel before it is drawn or formed into welding electrode. The purpose for this high degree of testing of the raw material is to ensure a tight chemistry range, and to have the ability to segregate product that deviates from this control window. Even a slight deviation outside of this chemistry range can have a dramatic effect on welding performance – despite the fact that the chemistry may still meet the AWS classification (for instance, not all ER70S-6 solid GMAW wires perform the same).
The second reason that a “mill cert” does not provide a completely accurate picture of the chemistry of the electrode or weld deposit is that there are almost always chemical components added to the wire during the manufacturing process. For example, flux cored tubular wires have shielding ingredients within the middle of the wire, while stick electrodes have flux extruded on the outside of the steel core. Even solid wires for use in GMAW and SAW welding usually have a copper layer adhered to the surface of the wire.
Now that we have established that a mill cert is not a CMTR, what precisely are the contents of a CMTR?
First, a CMTR shows that the issuer (manufacturer or distributor) accepts responsibility for the contents of the document and has a quality system in place to ensure the validity of the information, such as compliance to ISO 9001 or compliance to ASME NCA-3800. Once this is established, mention is given to the organizations that have provided the third-party verification of the issuer’s quality system. These third-party organizations include the American Society of Mechanical Engineers (ASME; New York, NY), American Bureau of Shipping (ABS; Houston, TX), Det Norske Veritas (DNV; Bærum, Norway) and/or other organizations.
Of course, the product being certified is listed, and the information regarding the purchase order number may also be disclosed. Similarly important is a statement declaring unequivocally that the product meets all of the requirements of the applicable specification. And finally, the signatures of the responsible personnel for the contents of the CMTR at the issuing corporation must be present, attesting that the statements are accurate and that the product has been tested in accordance with the stated requirements.
Now that the contents of a CMTR have been established, to what criteria should the product to be tested?
The AWS A5.01 Filler Metal Procurement Guidelines document provides testing “schedules” for welding electrodes. These are listed in Table 1 of that document, and are defined as follows:
F – The manufacturer’s standard testing schedule.
G – Tests from production runs of the product within 12 months preceding the date of the purchase order.
H – Chemical analysis only, for each lot shipped.
I – Tests called for by [A5.01] Table 2, for each lot shipped.
J – All tests which the classification called for in the pertinent AWS, ISO or other welding consumable standard, for each lot shipped.
K – All tests specified by the purchaser, for each lot shipped.
The results of tests conducted in accordance with schedules F and G will generally not appear on a CMTR, but rather in the series of basic “certificates of conformance” (COC). These results listed on a COC are generated by testing a sample of “off-the-shelf” product that was made under the supplier’s standard manufacturing and quality processes. However, the testing information in a COC are the results of tests that are conducted, as shown above by the definitions of Schedule F and G, either once every year or at intervals set out in the manufacturer’s testing schedule.
These COCs are fundamentally different, providing “typical” results; whereas a CMTR includes the “actual” results from testing conducted using a sample that is representative of the specific lot of product being furnished, rather than “off-the-shelf” product. The lot-specific results of Schedule H, I, J and K testing would appear on a CMTR, as the indicated by the phrase “for each lot shipped” in the schedule definitions.
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About the Author: Regis Geisler III is a registered Professional Engineer, Specials Certification Engineer and AWS Certified Welding Inspector who has worked the last eleven years at The Lincoln Electric Company, 22800 Saint Clair Avenue, Cleveland, OH 44117-8542, 216-481-8100, Fax: 216-486-1751, www.lincolnelectric.com. For questions or comments on this column, contact Regis at firstname.lastname@example.org.