When the code (section QW 403.6) specifies this clause does not apply when a WPS is qualified with a PWHT above the upper transformation temperature, what temperature is it referring to? I assumed that this upper temperature was the quenching temperature? The reason I ask is I am looking for the clause in ASME that allows you to, for example, qualify on 19mm and weld down to 4.76mm if you use PWHT.
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ASME IX PWHT
- Thread starter Cliffzer
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This is the temperature at which all of the steel becomes austenite. It doesn't apply to austenitic stainless steels because they do not transform. For Carbon and low alloy steel, it is often referred to as annealing, Normalizing, or (austenitizing) Quench and tempering. If you apply one of these PWHTs, you would be qualified down to 3/16" with a 3/4" thick weld test coupon with CVN requirements. However, if you haven't done it a lot, there are several pitfalls. For starters, it is expensive, and if you have to temper afterwards, you have to do 2 cycles instead of one. Also, most filler metals are not designed to be heat treated above the upper transformation temperature, and they can loose a lot of strength. Also, your parts can distrort and you can get of scaling. Sometimes the heat treatment itself can open up defects on the part which then have to be repaired and re-heat treated. It's not always the best way to go if you can avoid it, but it does have some advantages too. (less residual stress, usually better CVN properties, more corrosion resistance for stainless steel) If you are going to be doing this a lot, I would reccomend qualifying a procedure without a PWHT above the upper transformation temperature for your thicknesses, but if it is a one time thing and your procedure is already qualified, it may be worth it.
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Firstly, GRoberts thanks for the time taken to reply. So, for a CMn steel typically normalised at 920°C then QW403.6 says that if I PWHT above 920°C then I can weld down to 3/16"? Not that I want to PWHT at that temp, but I was always lead to believe that if you PWHT a weld then the 5/8" restriction does not apply. So really my question is where does it state in ASME IX that if you use PWHT then you can weld down to the lower limits stated in QW451 without the 5/8" restriction?
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Now that does make more sense.
Basically, the lower transformation temperature is the temperature at which some of the Ferrite starts to change into Austinite (In transformable steels of course). The upper transformation temperature is the point where all the change (from ferrite to austenite)is done. The temperature range between these temperatures is called intercritical. (That would be QW-407.1(5)) As examples, on low carbon steel, a typical lower transformation temperature (Also called the Ac1 temperature) could be about 1300F. A typical upper transformation temperature (Also called the Ac3 temperature) could be about 1550F.
Basically, the lower transformation temperature is the temperature at which some of the Ferrite starts to change into Austinite (In transformable steels of course). The upper transformation temperature is the point where all the change (from ferrite to austenite)is done. The temperature range between these temperatures is called intercritical. (That would be QW-407.1(5)) As examples, on low carbon steel, a typical lower transformation temperature (Also called the Ac1 temperature) could be about 1300F. A typical upper transformation temperature (Also called the Ac3 temperature) could be about 1550F.
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