Hi mecham, I agree E7018 is a bad choose, regarding your query, the operating pressure is 8MPa (1160PSI), our goal is replace the valve, unfortunately we have not that valve in our warehouse, and the new valve will come in four months, the seal weld will be a temporary corrective action to avoid the leakage.
I will choose between ENiCrFe3 and E309 to perform the temporary seal weld.
ASME B31.3 Table 330.1.1 Preheat Temperatures for P-1 Base Metal Group (SA 216 WCB) only has Recommended Minimum Preheat 70ºC/175ºF for materials 1" thick and greater.
ASME B31.3 Table 331.1.1 Requirements for Heat Treatment (PWHT) is 593–649ºC & 1,100–1,200ºF with a hold time of 2.4 min/mm or 1 hour/inch for materials greater than 3/4" (20MM).
I'll take the liberty of making a couple of comments.
1. You say that the valve operating pressure is 1160 psi, but the valve body shows the number 900 on it, which means that the valve design pressure is 900 psi. Are you sure you people have chosen the right valve?
2. Is the valve located on the boiler outlet nozzle to prevent backflow of steam? In this case, good engineering practice recommends to install a stop check valve, which your valve is not. Also in this case, the valve won't fall under ASME B31 (1 or 3, depending on the plant in which the valve is installed) but under ASME Section I (Power boilers). In fact, piping leaving a boiler, up to and including the first valve, falls under ASME Section I.
Giovanni S. Crisi
Sao Paulo - Brazil