Low-Temperature Carbon Steel
ASTM A420 WPL6 Buttweld Pipe Fittings
The standard low-temperature carbon steel grade for buttweld fittings — elbows, tees, reducers and caps to ASME B16.9 / B16.28, 1/2" to 48" NB, SCH 20 to XXS. Charpy V-notch impact tested to −46°C, EN 10204 3.1 / 3.2 traceable.
Where WPL6 Is Used
- ✓ LPG, propane and ammonia storage and transfer lines
- ✓ Refrigeration and cold-service process piping
- ✓ Ethylene and gas-processing plants where carbon steel must stay tough below freezing
- ✓ Outdoor piping in cold climates
WPL6 Compared With Related Grades
| Grade | Service | Key difference |
|---|---|---|
| A234 WPB | Ambient and elevated temperature | No impact test required by the standard |
| A420 WPL6 | Low temperature | Charpy impact tested at −46 °C |
| A420 WPL3 | Lower temperature | 3.5% nickel steel, impact tested at −101 °C |
| A403 WP304L / WP316L | Cryogenic (LNG) | Austenitic stainless, no ductile-to-brittle transition |
How to Specify WPL6 Fittings on a Purchase Order
A complete order line avoids clarification rounds. Example:
Elbow 90° LR, 4" SCH 80, ASTM A420 WPL6, ASME B16.9, Charpy impact test at −46 °C, EN 10204 3.1
- ✓ State the impact test temperature if your design needs one below −46 °C, so the grade can be reviewed
- ✓ Add NACE MR0175 / ISO 15156 if the line is in sour service
- ✓ Add IBR Form IV (Part D) (formerly Form III-C) if the line is under the Indian Boiler Regulations
Grade Overview
ASTM / ASME A420 WPL6 is the standard low-temperature carbon steel grade for wrought buttweld pipe fittings. It is a carbon-manganese steel produced and normalised to guarantee notch toughness in cold service, and is mandatorily Charpy V-notch impact tested at −46°C (−50°F). Fittings are formed from A333 Gr. 6 seamless pipe and heat treated to meet both the strength and impact requirements of the specification.
WPL6 is specified for LNG, ethylene, ammonia, refrigeration and other low-temperature process and utility piping where carbon steel must remain ductile below ambient. For steam and boiler service, the moderate-temperature grade A234 WPB is used instead.
Chemical Composition — A420 WPL6
| Element | Requirement | Note |
|---|---|---|
| Carbon (C) | ≤ 0.30% | Weldability / toughness balance |
| Manganese (Mn) | 0.50 – 1.35% | Strength & toughness |
| Silicon (Si) | 0.15 – 0.30% | Deoxidiser |
| Phosphorus (P) | ≤ 0.035% | Impurity limit |
| Sulphur (S) | ≤ 0.040% | Impurity limit |
| Ni, Cr, Cu, Mo, V | Residual limits | Ni ≤0.40, Cr ≤0.30, Cu ≤0.40, Mo ≤0.12, V ≤0.08 |
Mechanical Properties — A420 WPL6
| Property | Requirement |
|---|---|
| Tensile Strength | 415 – 585 MPa (60 – 85 ksi) |
| Yield Strength (min) | 240 MPa (35 ksi) |
| Elongation (min) | ≥ 22% (longitudinal, per specification formula) |
| Charpy Impact | Tested at −46°C — 18 J avg / 14 J min (per NPS) |
| Heat Treatment | Normalised (or normalised & tempered) |
Equivalent Grades
| Product Form | Specification |
|---|---|
| Buttweld fittings | ASTM / ASME A420 WPL6 |
| Seamless pipe | ASTM A333 Gr. 6 |
| Forgings / flanges | ASTM A350 LF2 |
| Plate | ASTM A516 Gr. 60 / 70 (impact tested) |
EN 10253 equivalent: see WPL6 pipe fittings on arshyapipefittings.com, and the closest European low-temperature grade EN P275NL1 (1.0488).
Fitting Types Available in WPL6
- Elbows — 45° / 90° / 180°, LR & SR (B16.9 / B16.28)
- Tees — equal & reducing (B16.9)
- Reducers — concentric & eccentric
- Caps — buttweld end closures
- Stub Ends — Type A & B for lap joints
- Laterals & Crosses — branch connections
Related grades: WPB · 304L · 316L · Flanges · IBR grades list
Testing & Inspection — WPL6
- Charpy V-notch impact test at −46°C on every heat — 18 J average / 14 J minimum, the property that defines WPL6.
- Chemical analysis of each heat, with fine-grain practice for low-temperature toughness.
- Tensile and hardness tests to ASTM A420 (415–585 MPa tensile, 240 MPa min. yield).
- Dimensional and visual inspection to ASME B16.9; NDE (MT / UT / RT) as specified in your purchase order.
Dimensions & Size Range — ASME B16.9
WPL6 fittings are made to ASME B16.9 (long-radius) and ASME B16.28 (short-radius elbows) dimensions, from 1/2" to 48" NB and above, in schedules SCH 20 to SCH 160 / XXS. Wall thickness matches the connecting pipe schedule. Centre-to-end dimensions for the most-ordered sizes:
| NPS | Outside diameter (mm) | 90° LR elbow “A” (mm) | 45° LR elbow “B” (mm) | Equal tee “C” (mm) |
|---|---|---|---|---|
| 1/2" | 21.3 | 38 | 16 | 25 |
| 1" | 33.4 | 38 | 22 | 38 |
| 2" | 60.3 | 76 | 35 | 64 |
| 3" | 88.9 | 114 | 51 | 86 |
| 4" | 114.3 | 152 | 64 | 105 |
| 6" | 168.3 | 229 | 95 | 143 |
| 8" | 219.1 | 305 | 127 | 178 |
| 10" | 273.1 | 381 | 159 | 216 |
| 12" | 323.9 | 457 | 190 | 254 |
| 16" | 406.4 | 610 | 254 | 305 |
| 20" | 508.0 | 762 | 318 | 381 |
| 24" | 610.0 | 914 | 381 | 432 |
Long-radius elbows have a centre-line radius of 1.5 × NPS; short-radius (ASME B16.28) 1.0 × NPS. Full tables to NPS 48, reducing tees, reducers and caps are available with every quotation. For EN 10253 dimensions see arshyapipefittings.com.
Export Documentation & Packing
We ship WPL6 fittings to projects outside India with the documents EPC contractors and inspection agencies expect:
- Mill test certificate — EN 10204 3.1 as standard; 3.2 with third-party witness
- Third-party inspection — Bureau Veritas, TÜV, Lloyd’s Register, SGS, DNV or the client’s own inspector
- Traceability — every fitting marked with grade, size, schedule and heat number, matching the certificate
- Packing — seaworthy wooden cases or pallets, bevel ends protected with end caps
- Shipping documents — commercial invoice, packing list and certificate of origin; FOB, CFR or CIF terms
Send your BOQ through the RFQ form (Excel or PDF attachments accepted) or on WhatsApp — quotations are usually issued within 24 hours.
WPL6 Fittings — Frequently Asked Questions
What is the difference between WPL6 and WPB?
Similar carbon steel chemistry and strength, but WPL6 is normalised and Charpy impact tested at −46°C, so it can be used in low-temperature service. WPB is not impact tested and is limited to −29°C.
Can fittings be dual-certified A234 WPB / A420 WPL6?
Yes — when a heat meets the chemistry, tensile and impact requirements of both specifications, fittings can be certified to both, which simplifies stocking for projects that use both grades.
What is the lowest design temperature for WPL6?
−46°C (−50°F), the Charpy test temperature. For colder service such as LNG, see cryogenic fittings for LNG service.