According to AWS A3.0-94: Interpass temp is the temperature of the weld area between weld passes.
I have seen other documents refer to it as the temperature just prior to beginning the next weld pass.
You measure interpass temp using either a temperature indicating crayon (temp-stik) or some sort of thermometer (we use an IR unit from Raytek, which can be had for about $100).
I've read a bit about how high interpass temperatures adversely effect material toughness. I've seen high interpass temperature effect qualification efforts on hardened aluminum (high interpass = unacceptably low tensile values).
If you need more information, you're going to have to wait for Nikie J.
Good luck
Charles Hall
Hi Brian
Just saw your next post on this.
As stated in the last post, there are a number of factors that influence this, but I will try to give you some idea.
The higher the temperature of a base material, the slower the cooling will be. (The quenching effect of the base material will be lessened, the higher the temperature.) If impact properties are important, then you would usually want to ensure as fine a grain size as possible. This is usually achieved by fast cooling. Without impact requirements, I would typically specify max interpass temps on ordinary C-Mn steel of 300°C max. When impact properties are required, I would typically reduce this to around 200°C. (These are rules of thumb, because there are other factors that also play a role, such as material thickness, welding process heat input etc.)
The slower the cooling, the wider the HAZ. If a narrow HAZ is required, then a lower max interpass temp will be specified. This is typically the case when welding quench and tempered steels, or precipitation hardened alloys or cold worked alloys that can not be heat treated.
In the case of certain alloys, deleterious microstructures form when the cooling is too slow. A typical example is the formation of carbides in Austenitic stainless steels when they spend extended periods in the temperature range of around 400 - 700°C. (I may be slightly out on this temp. - too lazy to check it right now.) We therfore want them to have low interpass temps., so that they will move through this range as fast as possible. Typically 175°C would be a maximum interpass temperature for these alloys.
I hope this answers your question.
Regards
Niekie Jooste
Fabristruct Solutions
Hi Brian
I am not sure if you are asking how to decide on what should be the highest interpass temperature to ensure that mechanical properties are optimized, or how it is actually determined in practice.
In my opinion, this is a very important parameter under certain circumstances, while at other times, it is very difficult to get it too high. It is also my opinion that mostly this parameter is applied and measured under such varying conditions, that the scatter in results is very large. In some instances, it is almost meaningless.
If you want guidance on the maximum interpass to specify under certain circumstances, then it would be better if you rather give your specific circumstances (material, thickness, impact properties required or not etc) because a person could write all day on this subject ans still not give the right answer you are looking for.
Regarding the way it is measured, I will give you some ideas, as I have applied it, but there will certainly be many people out there that can help me right here, and add additional "good ideas".
The interpass temperature can be thought of as the pre-heat temperature between runs. It needs to be at least as high as the initial pre-heat. The interpass temperature is therefore measure just before the weld pass is about to be deposited. It should be measured as close to the point where the arc is to be struck as is practical.
Obviously, if you find that the temperature is higher than the maximum interpass temperature specified, you will have to wait for the temperature to decrease to below this value.
Why is it important to keep the interpass temperature below a maximum value under certain circumstances? It is because the temperature of the base material is one of the governing factors of how fast the heat will flow out of the weld area. Under certain circumstances we want this to happen as fast as practical, to ensure that we avoid forming certain deleterious microstructures, or to keep the Heat Affected Zone (HAZ) as narrow as possible etc.
If this does not answer your question adequately, please ask again, giving more specific information.
Regards
Niekie Jooste
Fabristruct Solutions
Hi Niekie,
On some procedures interpass is determined by Yield requirments. We have PQRS to determine the yeild at different interpass's with different fillers. The higher the interpass the yield takes a dip.
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