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.
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) |
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