Specifications

Chemical composition and mechanical properties

Limits for plate, sheet and strip to ASTM A240. Pipe (A312), tube (A249, A269) and bar (A276, A479) limits are similar.

Values for plate, sheet and strip; check the standard for other product forms and thicknesses.

The mechanical values shown are for A240 plate; pipe and tube requirements in A312, A269 and A249 are similar and are reported on the mill test certificate.

Seawater and chloride service

With a PREN of at least about 42, SMO 254 pipe resists pitting and crevice corrosion in natural seawater at moderate temperatures, and in brackish and chlorinated water. It is used for seawater cooling and firewater lines on offshore platforms, seawater intake and reverse-osmosis lines in desalination plants, and heat exchangers cooled by seawater. SMO 254 instrument tubing is used offshore for hydraulic and control lines exposed to salt spray, where 316L tubing suffers crevice corrosion under clamps and supports.

Seamless or welded

Seamless SMO 254 pipe is used in smaller sizes and heavier walls. Welded pipe to A312 and A358 is widely used in larger sizes and thinner walls, and welded tube to A249 is standard for heat exchangers. Welded products are made with over-alloyed filler or autogenous welding followed by solution annealing so the weld matches the corrosion resistance of the base metal.

Fabrication

SMO 254 pipe is welded with over-alloyed nickel-based fillers such as ERNiCrMo-3 or ERNiCrMo-4, with argon backing for the root, low heat input and controlled interpass temperature. Heat tint is removed and welds pickled. Tubes are expanded into tube sheets in the annealed condition.

Ordering SMO 254 pipes and tubes

Please give the specification, seamless or welded, outside diameter or nominal size, wall thickness or schedule, length, end finish, quantity and any testing such as G48 pitting test, PMI or third-party inspection. Pipes and tubes are packed in wooden boxes with end caps, and each length is marked with grade, specification, size and heat number.

Where SMO 254 pipe is used

Offshore platforms: seawater cooling water, firewater ring mains and deluge systems, and hydraulic and chemical injection tubing exposed to salt spray. Desalination: seawater intake and reverse-osmosis feed lines at moderate pressure, and evaporator tubes in thermal plants. Power and process plants: seawater-cooled condenser and heat exchanger tubes. Pulp and paper: bleach plant filtrate and chemical lines. Chemical plants: chloride-contaminated acids and brines. In each case SMO 254 replaces 316L where pitting and crevice corrosion would shorten life, and competes with super duplex, which is stronger but less formable.

Testing

Each length of pipe and tube is hydrostatically or electrically tested as the specification requires. Many purchasers add a pitting test to ASTM G48, positive material identification and, for heat-exchanger tubes, eddy-current testing. The mill test certificate reports chemistry – including molybdenum and nitrogen, which control PREN – and mechanical properties.

Applications and related products

SMO 254 pipes and tubes are used for seawater systems, desalination, heat exchangers, offshore instrument tubing, bleach plants and chloride-bearing chemical processes. Matching products include SMO 254 sheets and plates, SMO 254 round bars, SMO 254 flanges, SMO 254 pipe fittings. Background on the alloy is on the SMO 254 page. Other materials are on the seamless pipes and tubes page.