Requirements 3 and 4 are not so easy. Heat input is calculated by multiplying voltage x current x 60 and dividing by travel speed. During welding, voltages and currents vary depending upon a number of factors, including the distance from the electrode to the work piece. Travel speed can also vary, especially in manual welding processes. In producing weld repairs, travel speed is very difficult to control, even if repairs are produced with stringer beads. Many in the industry believe the only way to maintain a level of heat input that does not deviate by more than ±10% is to employ automated welding methods, which would not be useful for repair welds.
The qualified thickness restrictions are also problematic from a cost standpoint. For example, assume a valve company produces a wide range of valve sizes and pressure classes. In order to be able to produce valve bodies ranging from 1-inch through 10-inch nominal size, in ASME pressure classes ranging from 150 through 2500, the company would have to be prepared to weld repair on wall thickness ranging from 0.25 inch (1-inch Class 150 minimum body wall) through at least 7.875 inches (10-inch Class 2500 flange thickness). This would require nine PQR specimens of graduated thickness starting at 0.313 inches thick, and increasing by 50% each step. The final coupon would need to be at least 6.3 inches thick. The costs to procure all of the raw material, machine the coupons, weld the coupons and perform all the necessary testing are very high. There also is no guarantee all of the coupons will pass all of the tests on the first attempt.
Add to this the fact that most projects calling for NACE MR0103-compliant duplex also carry extra requirements such as low-temperature impact testing and special corrosion tests, and the costs and opportunity for failure of qualification tests increases even more.
The appropriate welding procedures would need to be developed not only at the sites where the castings are machined (in case they run across any casting defects during machining), but also at each foundry that would be supplying castings.
Considering all of these issues, it is difficult to justify proactively developing the welding procedures when considering the low number of requests for duplex stainless-steel valves for refining applications, especially where NACE MR0103 compliance is also required. Without appropriate welding procedures, it is virtually impossible to quote NACE MR0103-compliant duplex stainless-steel valves.
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