Do seat ring welding rods need to be pre-heated? I've been told that they do not. The supplier we use preheats the overlay rods but they told me that seat ring rods are always the same material which I believe is copper.
We are preparing for an API 600 monogram and I am not sure what this procedure should be.
It is good practice to always preheat welding rods. When it comes to making a decision to preheat or not to preheat welding rods the answer is "when in doubt preheat"
Now to really address your question. It is the responsibility of the manufacturer to develop QA/QC procedures that translate  into meeting any set standard that you put as the goal, such as API or ISO ect.
The welding procedures that you will or have to use in order to comply with a standard, are particular to your manufacturing facility. The reason is that when it comes to welding there are so many variables that affect the outcome that only you can develop the procedures that will allow you to meet the set standard.
Equipment, welding method,Rod or wire or powder quality, Base material, overlay material, ambient temperature, humidity and base material temperature. All of this this factors could or would affect the overly outcome. Only you can know this conditions thereby developing your own procedures.

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