GRADE GUIDE · INCONEL 625
Inconel 625 (UNS N06625) is the general-purpose high-performance nickel alloy: a nickel-chromium-molybdenum-niobium chemistry that shrugs off seawater, sour gas and hot oxidising service from cryogenic temperatures up to about 980 °C. When one alloy has to cover corrosion and heat at once, 625 is the usual answer.
Also listed as: UNS N06625 · EN 2.4856 · NiCr22Mo9Nb · Alloy 625
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625's range is the reason it turns up everywhere in Gulf energy work: weld overlay on sour-service valves and wellheads, seawater piping and bellows, flare tips running red-hot, heat-exchanger bundles in aggressive process streams. The molybdenum and niobium stiffen the nickel matrix without heat treatment — the alloy is strong as-welded, which is exactly what overlay and repair work needs.
The price of that versatility is the alloy surcharge: 625 costs many multiples of stainless, so buying full plates for small jobs hurts. Off-cuts change that arithmetic — overlay drops, pipe stubs and plate remnants from oil & gas fabricators carry full certification at surplus prices. Check the MTC badge; for sour service, the certificate is the material.
Mostly oil & gas: weld overlay on sour-service components, seawater and produced-water piping, flare and burner parts, exchanger tubing. Anywhere chlorides, H2S or heat would retire a stainless grade.
It welds readily — it is itself a favourite filler wire — but machines hard and work-hardens, so rigid setups, sharp tooling and positive feeds are the rule. Budget more machining time than for stainless.
For hot reducing acids and wet chlorine chemistry, C-276's higher molybdenum wins. For mixed duty — seawater plus heat plus sour gas — 625 remains the broader tool.