Making a repair weld on an unknown material? Here are some tips to help you identify what it is you’re welding. Getty Images

Q: My work involves performing machine shop welds and repairing machinery and structures in the field. I almost never have the benefit of being told what type of metal I’m welding. Can you please provide some guidance on how I might determine what type and grade of metal I am working with?

A: The best advice I can give is if you don’t know what it is, don’t try to weld it. This especially applies to critical parts for which failure can cause injury or death.

Welding on some metals using welding procedures that are not appropriate can cause defects in the base metal, the weld, or both.

When you’re asked to weld an unidentified material, how can you determine what it is? First, you should be able to narrow down the possibilities using a basic evaluation. Look at the surface of the material and see how heavy it is. This should allow you to put the material into the broad categories, such as carbon or low-alloy ferrous material, stainless steel or nickel alloy, or aluminum alloy. Evaluating the area where you’ll need to make a weld can also provide you with important clues. Is there evidence that the part was welded during original manufacture? If so, that is a good indicator that the material is weldable. Is there evidence that a previous weld repair was attempted? If previous weld repairs have failed, this is a red flag telling you to be very sure of what you are working with before attempting a new repair.

If you are doing a repair on a piece of equipment, you could call the original manufacturer to ask what material was used. Some items usually are made from a certain material. For example, aluminum handrails typically are made using grade 6061. Doing a little research on materials commonly used to make the item to be welded can help you narrow down your options.

Since you work with a machine shop, you should be able to get some very good information on the material from the machinists. If it was new material that they machined, the machinist may know exactly what it is. They can give you some good information on the material based on its machining characteristic. You should be able to estimate the hardness of a steel based on the feed rate and speed used in the machining process. The way machining chips form also provides helpful information. You should avoid welding steels that produce small chips, as these are likely to be a free machining grade that is prone to hot cracking when welded.

Spark testing on steel and cast iron can give you a general idea on how much carbon the material contains. Chemical spot testing can also determine if specific alloying elements are present.

Chemical analysis will provide some of the best information to help identify the material grade. In many cases, you can submit machining chips from the material for analysis. If machining chips are not available, if possible remove a small piece of the material to submit for analysis—approximately 1-in. square. Chemical analysis of metals is available from most testing labs and in many cases costs less than $200.

The bottom line is that spending some time and maybe a little money to get a very good idea of what material you will be welding is important if you want to make a repair that is safe and will last.

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