ASTM A420 WPL6 Fittings – Low-Temperature Carbon Steel

ASTM A420 WPL6 is a wrought carbon steel butt-welding fitting for low-temperature service, Charpy V-notch impact tested at −46 °C (−50 °F), with a minimum yield strength of 240 MPa (35,000 psi) and a minimum tensile strength of 415 MPa (60,000 psi). Dimensions follow ASME B16.9 for sizes from NPS 1/2 to NPS 48.

Size range and specification

• Size range NPS 1/2 – NPS 48 (DN 15 – DN 1200), seamless or welded
• Types 45° and 90° elbow, 180° return bend, equal and reducing tee, concentric and eccentric reducer, cap
• Radius Long radius R = 1.5 D, short radius R = 1.0 D, 3D / 5D on request
• Wall thickness SCH 10 – SCH XXS, matched to the connecting pipe schedule
• Ends Beveled to ASME B16.25 for butt welding; plain end on request
• Surface treatment Shot blasted, black painted, anti-rust oil, or with 3PE / FBE coating
• Manufacturing process Seamless (hot formed from pipe) or welded (formed from plate and welded)
• Heat treatment Supplied in the normalized condition; the Charpy test is performed after the final heat treatment
• Delivery standard ASTM A420 / ASME SA420, dimensions to ASME B16.9

How this grade is supplied

• Inspection Inspected by the producing mill’s own inspection department, independent of production, against the delivery standard above. Third-party inspection — SGS, BV or TUV, or an inspector you send yourself — can be arranged at the mill or before shipment.
• Certificate A mill test certificate to EN 10204 3.1 showing the heat number, chemical composition, tensile results and Charpy impact results is standard. EN 10204 3.2, countersigned by the inspector you nominate, is available on request.
• Documents with the goods The mill test certificate and the packing list travel with the shipment, and the heat number is traceable from cast through to the finished fitting.
• Packing Sea-worthy export packing: bundled by size with end protection, corrosion protection on request, stencilled with the size, grade and heat number.
• MOQ One bundle or one truckload; mixed sizes within a bundle accepted.
• Lead time Counted from order confirmation. Stock sizes 5–10 days; mill run or non-stock 3–5 weeks. The delivery window is fixed on the quotation.
• How we supply Sourced through partner mills; the producing mill is named on the quotation.

ASTM A420 WPL6 chemical composition (maximum unless a range is given, %)

Silicon, nickel, chromium, molybdenum, copper and vanadium are also limited by ASTM A420 Table 1; the complete elemental limits are read from that table. Source: chemical composition requirements of ASTM A420 / ASME SA420, Table 1. The standard is the governing document.

ASTM A420 WPL6 tensile and impact requirements

The impact test temperature is a test condition, not a use temperature: a fitting impact tested at −46 °C is qualified for low-temperature service only when the design, the wall thickness and the project specification say so. Confirm the absorbed-energy requirement against the current edition and the order. Source: ASTM A420 / ASME SA420 tensile and impact requirements. The standard is the governing document.

What WPL6 means, and why the impact test is the whole point

ASTM A420 is the specification for wrought carbon steel and alloy steel butt-welding fittings for low-temperature service. In the grade WPL6, the W stands for weldable or wrought, the P indicates pressure service and the L marks low-temperature; the 6 is the strength and toughness level, matched to the carbon steel plate grades used for low-temperature pipe. The grade exists because ordinary carbon steel becomes brittle below about −29 °C (−20 °F): WPL6 closes that gap by requiring a Charpy V-notch test at low temperature on every heat, so the fitting is supplied with measured toughness rather than an assumed value.

WPL6, WPB and A333 Grade 6 — which belongs on the line

The practical rule: on a low-temperature line, the pipe is A333 Grade 6 and the fittings are A420 WPL6. They are welded to each other, so the fitting must carry the same low-temperature toughness as the pipe. A234 WPB is the fitting for ordinary and high-temperature lines, where no low-temperature impact test is required.

Where the dimensions come from

ASTM A420 fixes the chemistry, the tensile properties and the impact test; it does not dimension the fitting. Dimensions come from ASME B16.9, which sets the centre-to-end, centre-to-centre and overall dimensions and their tolerances, and the bevel is prepared to ASME B16.25. Wall thickness is matched to the connecting pipe schedule, and that match is where most ordering mistakes start.

Ordering mistakes that cost a spool

• WPL6 assumed when only WPB was specified. The impact test is the whole point of WPL6; if the line needs low-temperature toughness, it must be written on the order, not assumed.
• Impact temperature left open. State the test temperature and the energy acceptance if the project specification sets a stricter value than the standard.
• Wall thickness left open. The fitting has to match the pipe wall, otherwise the bevel does not align and the welder has to build up the joint.
• Seamless assumed. Welded fittings are permitted by A420; if the project requires seamless, write it on the order.
• Certificate requirement left off. Low-temperature lines usually need EN 10204 3.1 as a minimum and often 3.2 with third-party countersignature; state which one the project accepts.

What to state on the enquiry

• Fitting type and angle: 45°, 90° or 180°, long radius or short radius, tee, reducer or cap.
• Nominal size and the matching pipe wall thickness or schedule.
• Material: ASTM A420 WPL6, and whether seamless is required.
• Impact test temperature and any energy acceptance above the standard minimum.
• Certificate: EN 10204 3.1, or 3.2 with third-party countersignature.
• Quantity and destination port.

Typical applications

• LNG and cryogenic transfer lines
• Low-temperature process and storage piping
• Refrigeration and cold-climate utility lines
• Offshore topside and onshore low-temperature service

Standards covered

• ASTM A420
• ASME B16.9
• ASME B16.25
• ASME B16.28

Frequently asked questions

Where to go next

• Butt Weld Elbow – butt weld elbows to ASME B16.9
• Butt Weld Tee – butt weld tees to ASME B16.9
• Butt Weld Reducer – butt weld reducers to ASME B16.9
• ASTM A234 WPB – the carbon steel fitting for moderate and high-temperature service
• ASTM A333 Grade 6 – the low-temperature pipe that WPL6 fittings join
• Low-Temperature Service – how the low-temperature line is put together
• Get a Quote – send the grade, size, quantity and destination port