ASTM A420 is the standard specification for pipe fittings of wrought carbon steel and alloy steel for low temperature service. These fitting, either of seamless or welded construction, are primarily used in pressure piping and pressure vessel service at low temperatures. Metals-Piping can provide all the four steel grades covered by ASTM A420: WPL6, WPL9, WPL3, and WPL8.

1. ASTM A420 Chemical Composition Requirements

Chemical Composition of ASTM A420
Elements	WPL6, %	WPL9, %	WPL3, %	WPL8, %
Carbon [C]	≤0.30	≤0.20	≤0.20	≤0.13
Manganese [Mn]	0.50-1.35	0.40-1.06	0.31-0.64	≤0.90
Phosphorus [P]	≤0.035	≤0.030	≤0.05	≤0.030
Sulfur [S]	≤0.040	≤0.030	≤0.05	≤0.030
Silicon [Si]	0.15-0.40	…	0.13-0.37	0.13-0.37
Nickel [Ni]	≤0.40	1.60-2.24	3.2-3.8	8.4-9.6
Chromium [Cr]	≤0.30	...	...	...
Molybdenum [Mo]	≤0.12	...	...	...
Copper [Cu]	≤0.40	0.75-1.25	…	…
Columbium [Cb]	≤0.02	...	...	...
Vanadium[V]	≤0.08	...	...	...

*For grade WPL6, the limit for Columbium may be increased up to 0.05% on heat analysis and 0.06% on product analysis.
*Fittings of WPL3 made from plate or forgings may have 0.90 % max manganese.
*Fittings of WPL8 made from plate may have 0.98 % max manganese.

2. ASTM A420 Mechanical Properties

ASTM A420/ A420M	Tensile Strength, min.		Yield Strength, min.		Elongation %, min
Grade	ksi	MPa	ksi	MPa	Longitudinal	Transverse
WPL6	65-95	415-655	35	240	22	12
WPL9	63-88	435-610	46	315	20	…
WPL3	65-90	450-620	35	240	22	14
WPL8	100-125	690-865	75	515	16	…

*All the elongation values are on the basis of standard round specimen, or small proportional specimen, min % in 4 D.

3. 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 Specimen	A*		B*
mm	ft·lbf	J	ft·lbf	J
10 by 10.0	13	17.6	10	13.6
10 by 7.5	10	13.6	8	10.8
10 by 5.0	7	9.5	5	7.0
10 by 2.5	4	5.4	3	4.1

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
Size of Specimen	A*		B*
mm	ft·lbf	J	ft·lbf	J
10 by 10.0	25.0	33.9	20.0	27.1
10 by 7.5	21.0	28.5	17.0	23.1
10 by 5.0	17.0	23.1	14.0	19.0
10 by 2.5	8.0	10.8	6.0	8.1

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)

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

4. 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 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.

5. 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.

6. Product & Standards

Standards	Product
ASME B16.9	Factory-Made Wrought Steel Butt Welding Threaded
ASME B16.11	Forged Steel Fittings, Socked Welding Threaded
ASME Section VIII Division 1	Pressure Vessels
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

7. Tests and Inspections

Pipe fittings manufactured to ASTM A420 shall take the following tests or inspections: dimensional inspection, visual examination, hydrostatic test(when required), chemical analysis, tensile test, impact test, radiographic test(RT).

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