Alloy Steel
Chrome-moly grades for elevated temperature pressure service. Refinery hydrotreater piping, power plant main steam, and high-temperature chemical reactor service all live here. F22 and F91 cover the bulk of installed plant. F92 is the modern high-temperature evolution.
F11 (1.25 Cr - 0.5 Mo)
Low-alloy chrome-moly for moderate elevated temperature service to about 1000 degrees F. Used on hot oil and intermediate-temperature steam service. Forging and welding are straightforward with standard low-alloy procedures.
F22 (2.25 Cr - 1 Mo)
The classic high-temperature alloy. Pressure-rated to 1100 degrees F. Refinery hydrotreater, hydrocracker, and FCC vapor service. Post-weld heat treatment mandatory on most welded sections to develop the temper structure and relieve residual stress. Charpy impact requirements vary by service specification.
F91 (9 Cr - 1 Mo - V - Nb)
Modified 9 chromium with vanadium and niobium microalloying. Operating temperature 1100 to 1200 degrees F. Power plant main steam and hot reheat headers. Welding and heat treatment are demanding. Preheat, interpass, and post-weld heat treatment temperatures are tightly controlled to avoid hard zones and Type IV creep cracking.
F92 (9 Cr - 0.5 Mo - 1.8 W)
Tungsten-substituted 9 chromium for higher creep strength than F91 at extreme temperature. Used on supercritical and ultra-supercritical power generation. Welding consumables and procedure development are project-specific.
A350 LF3 Low-Temperature Carbon-Nickel
Listed under alloy because of the 3.5 percent nickel content. Service down to minus 150 degrees F with charpy impact testing. Cryogenic LNG and refrigeration applications.