Oil and gas piping materials, matched to the service

Crude, product, fuel gas and most hydrocarbon process lines run in carbon steel because it is strong, weldable and cheap per metre. ASTM A106 Grade B is the default here. It is seamless only and is written for high-temperature service, so it goes on process lines, pump suctions and anything hot.

ASTM A53 Grade B comes seamless or welded and is common on firewater, cooling water, instrument air and structural pipe racks. Many mills certify a single pipe to both standards, which is handy for spares, but read the certificate before you assume it.

Above roughly 400 °C plain carbon steel loses creep strength and starts to graphitise over long periods. Fired heater outlets, reformer and hydrotreater lines and high-pressure steam headers therefore use chrome-moly. P11 (1¼Cr–½Mo) and P22 (2¼Cr–1Mo) under ASTM A335 are the two grades we handle. P22 holds strength at higher temperatures and resists hydrogen attack better, so it shows up where both heat and hydrogen are present.

Chrome-moly needs preheat and post-weld heat treatment, so fabricators often ask for the full chemistry on the certificate. We send it.

Corrosion, not heat, drives the choice in other units. 316L stainless covers amine units, condensate with chlorides and many instrument tubing runs. Where chlorides are higher or stress corrosion cracking is a risk, duplex steel gives roughly twice the yield strength of 316L and a much higher pitting resistance number.

Monel 400 handles seawater cooling and hydrofluoric acid alkylation units well, and is a long-standing choice for pump shafts and valve trim there. Inconel and Incoloy turn up in furnace internals and hot corrosive streams.

• Sour gas (H₂S) service: specify NACE MR0175 / ISO 15156 hardness limits on the enquiry so the grade and heat treatment can be confirmed.
• Chloride-bearing water above about 60 °C: consider duplex before 316L.
• Seawater intake and cooling: Monel or duplex for pumps, shafts and small-bore piping.