If I am hearing your question correctly and looking at the Tables just as correctly then I think you are miss using Table 4.5???
Table 4.5 is listing changes in your ESSENTIAL VARIABLES that would require you to do another PQR. The 100*F is for GTAW welding and it is a decrease in temperature of greater than 100* that would require a new PQR. And that is for either the initial pre-heat or the interpass temp.
This is not a conflict creating a different preheat between the two tables. One is the required pre-heat, which you see correctly based upon information given, at 50*F MINIMUM. The other says you can't change/decrease that by over 100*. Now, you would have to have your pre-heat at say 200*F on your original PQR (for whatever reason you had chosen to have it that high). Then, you would have to want to work at below 100* and would thus have to qualify a new PQR.
If you were at 140*F on the original. You could not go to the max of over 100* decrease because then you would be below the 50*F minimum. But, you could come down to 50* and still be approved with the original PQR because you didn't decrease the temp by over 100*.
And remember, this is all based upon the column, that I believe you used, for GTAW. All other processes require a new PQR with only a 25*F decrease. But, again, if you are at the miniumum you can't go any lower anyway. Now, you could raise your minimum to 75* and still be okay as to the code required minimum and not go over the 25* change and be good for both the PQR and code. BUT, to lower the minimum temp you would need to write a new WPS off the original PQR that allowed lower pre-heat. You can write several WPS's from one PQR. So, go ahead for the PQR and make your pre-heats higher, like the afore mentioned 150*, and then you can use it to write WPS's all the way down to the code minimum of 50*. Let's you have a broad range of application
List your actual minimum just as you have, that doesn't stop someone from pre-heating more just less, but it does limit your range as you write WPS's from it, BECAUSE, Then, the PQR meets the minimum Pre-heat and Interpass requirements. Then, you would need a different PQR if you wanted to use LESS pre-heat. But since you are at the minimum, you can't pre-heat any less anyway.
Hope that answers your question and I haven't misunderstood what you were asking. I got interrupted a couple of times as I wrote this and it does look a little disjointed at the end.
Have a Great Day, Brent
See, now that changes many things but not the bottom line. You do have to go within the established perameters of the PQR that was approved by testing without exceeding any differences according to Table 4.5. You can establish many different WPS's from the one PQR until you change something beyond the tolerances in that table. So, you can't write a WPS and do any welding based purely on Table 4.9 and/or Table 3.2. They must be within the allowed variable ranges you set for yourself by doing the original PQR to 125*. Now you MUST pre-heat to the 100* you said you were challenged for not being to. But, what does the WPS that was established from the PQR state. Because if it is written for 125*, you can't even come down to the 100* mark. The pre-heat must be to 125*. That is now your only working minimum. Forget tables 4.9 and 3.2. Forget the variables allowed in 4.5. Your PQR/WPS states 125*, then 125* it is. You can only come on down to 100* after you write and get approval for a new WPS at 100*. The table does not let you vary the temperature from the WPS, only lower the temperature from the PQR to write a WPS that has limited variations.
Have a Great Day, Brent
Hi Brent,
Table 4.5 item 35,36 (d) The production welding preheat or interpass temperature maybe less then the PQR preheat or interpass temperature provieded that the provisions of 5.6 are met. and the base metal temperature shell not be less than the WPS temperature at the time of subsequent welding.
pls help to explain what code state about this.
Thanks in advance
winai
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