ASTM A420 fittings

ASTM A420 standard specification

ASTM A420/A420M-07 Standard Specification for Piping Fittings of Wrought Carbon Steel and Alloy Steel for Low-Temperature Service.


1.1 This specification covers wrought carbon steel and alloy steel fittings of seamless and welded construction, covered by the latest revision of ASME B16.9, ASME B16.11, MSS SP-79, MSS SP-83, MSS SP-95, and MSS SP-97. Fittings differing from these ASME and MSS standards shall be furnished in accordance with Supplementary Requirement S58 of Specification A960/A960M. These fittings are for use in pressure piping and pressure vessel service at low temperatures.

1.2 Optional supplementary requirements are provided for fittings where a greater degree of examination is desired. When desired, one or more of these supplementary requirements shall be specified in the order.

1.3 This specification is expressed in both inch-pound units and in SI units. However, unless the order specifies the applicable “M” specification designation (SI units), the material shall be furnished to inch-pound units.

1.4 The values stated in either SI units or inch-pound units are to be regarded separately as standard. Within the text, the SI units are shown in brackets. The values stated in each system may not be exact equivalents; therefore, each system shall be used independently of the other. Combining values from the two systems may result in non-conformance with the standard.

Chemical Composition (%) of ASTM A420

All values are maximum unless otherwise indicated.

(1) For each reduction of 0.01% C below 0.30%, an increase of 0.05% Mn above 1.06% will be permitted, up to a maximum of 1.35%.
(2) Fittings made from forgings may have 1.35% max Mn.

Mechanical properties of ASTM A420

Tensile RequirementsWPL6WPL9
Tensile Strength
min, ksi [MPa]
Yield Strength
min, ksi [MPa]
Where the wall thickness lies between two values above, the min elongation value is determined by the following equations:

Longitudinal E=48t+15.00,E=48t+13.00
Transverse E=32t+6.50,E=32t+8.00
E = elongation in 2in [50mm], %
t = actual thickness of specimen, in [mm]

Impact Test Properties

Since these pipe fittings are primarily used for low-temperature service, the properties of Charpy V-notch impact test must be considered.

Charpy Impact Requirements for WPL6, WPL9, and WPL3

Size of SpecimenA* B* 
10 by 10.01317.61013.6
10 by 7.51013.6810.8
10 by 5.079.557
10 by 2.545.434.1
A*Charpy V-Notch Impact Value Required for Acceptance (Average of Three Specimens)

B*Minimum Charpy V-Notch Impact Value Without Requiring Retest (One Specimen Only of a Set)Charpy Impact Requirements for WPL8

Impact Test Temperature of ASTM A420

Grade°F [°C]
WPL6−50 [−45]
WPL9−100 [−75]
WPL3−150 [−100]
WPL8−320 [−195]

Heat Treatment

All fittings shall be furnished in the normalized, normalized and tempered, annealed, or quenched and tempered condition. All welding shall be completed prior to the austenitizing heat treatment. After forming, the fittings shall be allowed to cool below the lower critical before applying one of the heat treatments. When specified, post-weld heat treatment may be required.

Material and Manufacture

The raw material for these fittings shall be fully killed steel, consisting of forgings, bars, plates, sheet, and seamless or fusion welded tubular products(pipes, tubes, or cylinders).

The steels shall be made using recognized melting practices necessary to produce steels that shall meet the impact requirements of ASTM A420. The ASTM A420 fittings may be made by forging or forming operations, including operations, including hammering, pressing, piercing, extruding, upsetting, working, bending, fusion-welding, or machining, or by a combination of two or more of these operations. The forming procedure shall be so applied that it will not produce injurious defects in the fittings. All the fittings shall be furnished free of welding repair. The welded joints of the fittings shall be finished in accordance with the requirements of Paragraph UW-35 (a) of Section VIII, Division 1 of ASME Boiler and Pressure Vessel Code.

Conc. reducer 10″x6″(wt. 1.625″x1.062″),

Fitting standards and certifications

In pipe fittings as well, standards play a vital role. The manufacture and installation of pipe fittings is tightly regulated by various standards and codes.

  • ASME B16.9 -Factory-Made Wrought Steel Butt Welding Threaded
  • ASME B16.11 -Forged Steel Fittings, Socked Welding Threaded
  • MSS SP-25 – Standard Marking System for Valves, Fittings, Flanges, and Unions
  • MSS SP-79 -Socket Welding Reducer Inserts
  • MSS SP-83 -Steel Pipe Unions, Socket-Welding and Threaded
  • MSS SP-95 – Swage(d) Nipples and Bull Plugs
  • MSS SP-97 -Integrally Reinforced Forged Branch Outlet Fittings-Socket Welding, Threaded and Buttwelding Ends