WPL6 Low Temperature Carbon Steel Pipe Fittings
ASTM A420 WPL6 / EN 1.0473 (P215NL) — Rated to -46°C · Charpy Impact Tested · PED 2014/68/EU. Normalised low temperature carbon steel buttweld fittings for propylene refrigeration, LPG storage, CO₂ systems and cold climate piping. ASME B16.9. EN 10204 3.1 standard; 3.2 TPI on request.
-46°C
Min Design Temp
P-No. 1
ASME Group 1
Normalised
Mandatory Condition
½″–48″
Size Range
Request WPL6 Quote
Response within 1 business day
WPL6 Grade Equivalents
| Standard | Designation | UNS / EN Number | Notes |
|---|---|---|---|
| ASTM A420 | WPL6 | — | Low temp buttweld fittings |
| EN 10253-1 | P215NL | EN 1.0473 | European equivalent |
| ASME B16.9 | WPL6 | ASME P-No. 1, Gr. 1 | Same P-No. as WPB |
| ISO | P215NL | — | ISO 3419 (fittings) |
Minimum design temperature: -46°C (-50°F). WPL6 must be supplied in the normalised condition — as-rolled WPB is NOT an acceptable substitute for low temperature service.
Chemical Composition — ASTM A420 WPL6
| Element | C | Mn | Si | P | S | Ni | Cr | Mo | V |
|---|---|---|---|---|---|---|---|---|---|
| Limit | ≤0.30 | 0.29–1.06 | ≤0.35 | ≤0.035 | ≤0.035 | ≤0.40 | ≤0.40 | ≤0.15 | ≤0.08 |
Fine-grain practice is required for WPL6. Aluminium (Al) fine-grain treatment must be confirmed on the material test certificate. The combination of low carbon content, controlled Mn, and fine grain size underpins toughness at -46°C.
Mechanical Properties — ASTM A420 WPL6
| Property | Metric | Imperial |
|---|---|---|
| Tensile Strength | 415–550 MPa | 60–80 ksi |
| Yield Strength (Rp0.2) | ≥240 MPa | ≥35 ksi |
| Elongation (A50mm) | ≥22% | ≥22% |
| Impact — Charpy V-notch avg (at -46°C) | ≥20 J | ≥15 ft·lbf |
| Impact — Charpy V-notch individual min (at -46°C) | ≥16 J | ≥12 ft·lbf |
Charpy impact testing at -46°C is mandatory for all WPL6 fittings. Test results must appear on the EN 10204 3.1 material test certificate. Sets of three specimens are tested; no individual value shall fall below 16 J.
Heat Treatment — Normalising
WPB as-rolled is NOT acceptable for WPL6 service
Standard carbon steel buttweld fittings to ASTM A234 WPB are often supplied in the as-rolled condition and carry a minimum design temperature of only -29°C. WPL6 is a separate material specification requiring mandatory normalising heat treatment to achieve the fine-grain microstructure and impact toughness needed at -46°C. Always verify the heat treatment condition (normalised) on the material test certificate before use in low temperature service.
Supply Condition
Normalised — mandatory for WPL6. Fittings must be normalised after all forming operations.
Normalising Temperature
870–940°C, followed by air cooling. Ensures uniform fine-grained ferritic-pearlitic microstructure.
Fine Grain Practice
Aluminium or other grain-refining element addition is required. Stated in the chemical composition certificate.
Welding — WPL6 (ASME P-No. 1 Group 1)
WPL6 falls under ASME P-No. 1 Group 1 — the same group as standard carbon steel WPB. This significantly simplifies Welding Procedure Specification (WPS) qualification when transitioning from WPB to WPL6, as an existing qualified WPS for P-No. 1 may cover WPL6 subject to review of the impact requirements.
Filler Metal
ER70S-6 (GTAW/GMAW) or E7018 (SMAW). The E7018 low-hydrogen electrode is preferred for thicker walls to minimise hydrogen-induced cracking risk.
Preheat (per ASME B31.3 Table 330.1.1)
Minimum 10°C for wall thickness <25 mm; minimum 65°C for wall ≥25 mm. Higher preheat may be specified by the project WPS.
Post Weld Heat Treatment (PWHT)
Not mandatory for P-No. 1 under ASME B31.3 for standard wall thicknesses, but may be required by the project specification or client ITP for heavier wall joints.
WPS Qualification Note
ASME P-No. 1 Group 1 — same group as WPB. Existing P-No. 1 qualified procedures may be applicable; confirm impact test requirements with the responsible welding engineer.
Typical Applications
Propylene Refrigeration
Propylene refrigerant circuits at -40 to -46°C in ethylene plants and propane dehydrogenation (PDH) units. WPL6 is the standard material for propylene cold headers and cold box piping.
LPG Storage
Mounded and above-ground bullet LPG storage tanks and associated piping. Propane flash temperature reaches approximately -42°C; WPL6 provides the required toughness margin for tank nozzle and interconnection pipework.
CO₂ Refrigeration
Sub-critical CO₂ (R-744) refrigeration systems where the evaporating temperature drops below -29°C. Supermarkets and industrial cold stores operating at -35 to -46°C evaporator temperatures use WPL6 for low-side piping.
Cold Climate Piping
Outdoor process and utility piping in Canada, Russia, Scandinavia, and other regions with design ambient temperatures of -40 to -50°C. WPL6 is the minimum specification for uninsulated carbon steel piping in arctic-class installations.
Low Temperature Grade Comparison
| Grade | Specification | Min Design Temp | Key Notes |
|---|---|---|---|
| A234 WPB | ASTM A234 | -29°C (-20°F) | As-rolled standard carbon steel. No impact test. |
| A420 WPL6 | ASTM A420 | -46°C (-50°F) | Normalised, Charpy tested at -46°C. P-No. 1. |
| A420 WPL3 | ASTM A420 | -101°C (-150°F) | 3.5% Ni alloy steel. Charpy tested at -101°C. |
| A403 WP304L | ASTM A403 | -196°C (-320°F) | Austenitic stainless (FCC) — no ductile-brittle transition. |
Select WPL6 when the minimum design temperature is between -29°C and -46°C. For temperatures below -46°C, WPL3 (3.5Ni) or austenitic stainless (WP304L/WP316L) must be considered.
Request WPL6 Fittings Quote
Specify size, schedule, fitting type, design temperature, and required MTR (EN 10204 3.1 or 3.2). We respond within 1 business day.
Request a Quote →