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.

Sheet and plate production

Alloy 20 plate is hot rolled from slab, annealed and pickled; sheet and strip are cold rolled further to thinner gauges and annealed. Plates are supplied with a descaled surface, and sheets with a smooth cold-rolled finish suitable for forming and lining. Each sheet and plate is marked with grade, specification, heat number and dimensions.

Vessels, tanks and linings

Alloy 20 plate is used for acid storage and mixing tanks, pickling tanks and their heating coils and racks, reactor vessels and columns, and tube sheets and channels of acid coolers. For large vessels, carbon steel lined with Alloy 20 sheet, or clad plate, can reduce cost while keeping Alloy 20 on the wetted surface. Plate is cut by plasma or water-jet, formed cold with allowance for its strength and work hardening, and welded with matching filler.

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

Sheets are supplied in standard mill sizes and plates in hot-rolled widths and lengths, or cut to size by shearing, plasma or water-jet. Circles, rings and blanks for tube sheets and flanges can be cut from plate. Sheets are packed flat on pallets with interleaving to protect the surface, and plates on wooden skids. Each piece keeps the heat number of the parent plate for traceability through fabrication.

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 sheets and plates are used for sulphuric acid tanks and vessels, steel pickling equipment, phosphoric acid evaporators, chemical and pharmaceutical reactors, and heat-exchanger components. Matching products include Alloy 20 pipes and tubes, Alloy 20 round bars, Alloy 20 flanges and Alloy 20 pipe fittings. Background on the alloy is on the Alloy 20 page. Other materials are on our plates and sheets pages.