Specifications

Chemical composition and mechanical properties

Limits as given in the ASTM B specifications for N08020.

Pipe, bar and forging requirements are given in ASTM B464, B729, B473 and B462.

Actual values for each heat are reported on the mill test certificate.

Why Alloy 20

Alloy 20 is a niobium-stabilised nickel-iron-chromium alloy with molybdenum and copper, designed for sulphuric acid. It is chosen for sulphuric acid across a wide range of concentrations, phosphoric and nitric acids, pickling liquors and chloride-bearing water. Compared with 316L, Alloy 20 resists sulphuric acid and chloride stress corrosion cracking far better; compared with 904L it has higher nickel; for hot concentrated or heavily contaminated acids, Hastelloy C276 is used instead.

How we manufacture Alloy 20 fittings

Seamless fittings are formed from Alloy 20 pipe and welded fittings from B463 plate, welded with matching filler and radiographed as ASTM B366 requires. Elbows are formed by mandrel bending, tees by bulging or extrusion and reducers by pressing. After forming, fittings are annealed, pickled, bevelled to ASME B16.25 and inspected to ASME B16.9. Each fitting is marked with grade, size, schedule and heat number.

Fittings in acid lines

In acid service, fittings see the highest turbulence and erosion. Long-radius elbows and gradual reducers reduce local velocity and attack. Butt-weld fittings avoid the crevice of socket weld joints and are preferred for acid lines; forged socket weld and threaded fittings are used for small-bore vents, drains and instrument connections where the specification allows.

Welding and fabrication

Alloy 20 is welded by TIG, MIG and manual arc processes with matching ER320LR filler or suitable nickel-based fillers, on clean joints free of oil, paint, marking crayon, sulphur and lead, using low heat input and controlled interpass temperatures. Heat tint is removed and welds are pickled where corrosion resistance at the weld matters. Fabrication areas should be kept separate from carbon steel, and dedicated tools used to avoid iron contamination.

Testing and ordering

Common supplementary requirements are an intergranular corrosion test to ASTM A262, positive material identification and third-party inspection by the buyer's nominated agency. Please give the grade and specification, product type, size, schedule or class, quantity and any testing or inspection requirement with your enquiry. Each piece is marked with grade, specification, size and heat number, packed in wooden boxes or on pallets, and traceable to its mill test certificate.

Sizes, supply and packing

Fittings are supplied with ends bevelled to ASME B16.25 and matched to the pipe schedule, so that the bores align at each weld. Long-radius elbows are standard; short-radius elbows, 3D bends, reducing tees and eccentric reducers are made on request. Fittings are packed in wooden boxes with bevel protectors, and project orders can be marked with item numbers from the bill of materials to simplify receiving at site.

Certification and traceability

Alloy 20 is often confused with 300-series stainless steels and with other nickel alloys of similar appearance. Every piece carries its grade and heat number, and the mill test certificate reports the full chemistry – including nickel, copper, molybdenum and niobium – and mechanical properties. Positive material identification can be carried out before dispatch on request, and intergranular corrosion testing can be added where the end user specifies it.

Applications and related products

Alloy 20 pipe fittings are used in sulphuric acid plants, pickling lines, phosphoric acid and fertiliser plants, and chemical and pharmaceutical processing. Matching products include Alloy 20 pipes and tubes, Alloy 20 sheets and plates, Alloy 20 round bars and Alloy 20 flanges. Background on the alloy is on the Alloy 20 page. Fittings in other materials are on the pipe fittings page.