Specifications

Chemical composition

Nickel includes cobalt. Limits as given in ASTM B127, B164 and B165 (alloy 400) and B865 (alloy K-500).

Pipes and tubes are made in alloy 400; alloy K-500 is used mainly for bar and forgings. Background and equivalents are on the Monel page.

Mechanical properties

Size limits for each condition are given in ASTM B165. Annealed material is used where the pipe or tube will be bent, flared or expanded; stress-relieved material where higher strength is wanted.

Where Monel pipes and tubes are used

Seawater and marine: Monel 400 resists seawater and brackish water, including at high flow velocities, and is not prone to chloride stress corrosion cracking. It is used for seawater cooling lines, ballast and bilge systems, and pump and valve connections on ships and offshore platforms.

Hydrofluoric acid: Monel 400 is a standard material for HF alkylation units in refineries, handling hydrofluoric acid and its vapours across a wide range of concentrations and temperatures, provided air is excluded.

Refinery and chemical: Monel tubes are used in crude oil distillation overhead condensers, where chlorides and hydrochloric acid condense, and in brine heaters, evaporators and caustic soda concentrators.

Seamless or welded Monel pipe

Seamless Monel pipe to ASTM B165 is used for pressure piping, HF service and heat-exchanger tubing, where the absence of a weld seam is preferred. Welded Monel pipe to ASTM B725 is made from strip or plate and is used in larger diameters and thinner walls, where it is more economical. Both are supplied annealed and meet the same alloy requirements. The project specification normally states which is acceptable for each line.

Heat-exchanger tubes are ordered by outside diameter and minimum or average wall thickness, in straight lengths or as U-tubes. Tubes for condensers and evaporators are usually supplied annealed, so that they can be expanded into tube sheets without cracking, and are eddy-current or hydrostatically tested length by length. Instrument and small-bore Monel tubing is supplied in coils or straight lengths for compression-fitting connections in marine and chemical instrumentation.

Fabrication

Monel 400 pipe and tube bend and flare easily in the annealed condition and are welded with nickel-copper filler metal (ERNiCu-7) using TIG or MIG. Joints must be clean and free of sulphur and lead, which cause cracking. After fabrication, no heat treatment is normally needed for corrosion resistance. Tubes are rolled into tube sheets in the annealed condition for heat exchangers.

Ordering Monel pipes and tubes

Please give the specification, seamless or welded, outside diameter or nominal size, wall thickness or schedule, length, condition, end finish, quantity and any testing such as hydrostatic, eddy-current or ultrasonic tests, or third-party inspection. Pipes and tubes are packed in wooden boxes with end caps, and each length is marked with alloy, specification, size and heat number.

Applications and related products

Monel pipes and tubes are used in marine and offshore seawater systems, HF alkylation units, crude oil overhead condensers, brine heaters, caustic soda plants and chemical processing. Matching products include Monel flanges, Monel pipe fittings, Monel sheets and plates, Monel round bars and Monel fasteners. Pipes and tubes in other materials are on the seamless pipes and tubes page.