BS 4360 Grade 50 Double-Sided Submerged Arc Welding (DSAW) Steel Pipe
Basic Overview
BS 4360 Grade 50 DSAW (Double-Sided Submerged Arc Welded) steel pipe is a high-strength structural steel product that combines the now-withdrawn British Standard material grade with a robust, high-integrity welding process. Grade 50 is the higher-strength counterpart to Grade 43, with a minimum yield strength of approximately 355 MPa (51 ksi) , making it suitable for demanding structural applications such as high-rise buildings, bridges, offshore platforms, and heavy engineering projects.
While BS 4360 has been superseded by EN 10025 (with the modern equivalent being S355JR/S355J2), Grade 50 remains a widely recognized specification in legacy projects and in regions where familiarity with the British standard persists. DSAW is the preferred manufacturing method for large-diameter, thick-wall pipes used in demanding structural and low-pressure fluid applications.
Name Explanation
| Part | Meaning |
|---|---|
| BS | British Standard |
| 4360 | The withdrawn British Standard specification for weldable structural steels |
| Grade 50 | A high-strength carbon-manganese steel grade with a minimum yield strength of approximately 355 MPa (51 ksi) – the modern equivalent is S355JR/S355J2 |
| DSAW | Double-Sided Submerged Arc Welding – both inside and outside welds are applied; the welding arc is submerged in granular flux; separate welds consume a portion of each other forming a single high-quality weld nugget |
DSAW Manufacturing Process
Double-Sided Submerged Arc Welding is a high-efficiency process used primarily for large-diameter steel pipes:
Process Description
Welding arc is submerged in granular flux during welding, protecting the weld from atmospheric contamination
Both inside and outside welds are required, usually accomplished in separate processes
The separate welds consume a portion of the other, resulting in a single high-quality weld nugget
Forming Methods
| Method | Description |
|---|---|
| JCOE / JCO | Progressive J-C-O forming steps (J-shape → C-shape → O-shape), expanded after welding; this is the most common method for LSAW/DSAW pipes |
| UOE | Plate pressed into U-shape, then O-shape, expanded after welding |
Cold Expansion
Pipe may be expanded up to 1.5% to obtain final OD dimension
This process can result in a gain of yield strength
Expansion is most often utilized in UOE mills due to the need to recover yield strength lost during forming
Key Specifications
| Attribute | Description |
|---|---|
| Standard (Historical) | BS 4360 (withdrawn, replaced by EN 10025) |
| Modern Equivalent | S355JR / S355J2 (EN 10025-2) – minimum yield strength 355 MPa |
| Grade | Grade 50 – minimum yield strength approximately 355 MPa (51 ksi) |
| Manufacturing Process | DSAW (Double-Sided Submerged Arc Welding) / LSAW (Longitudinal Submerged Arc Welding) |
| Forming Methods | JCOE or UOE |
| Size Range | 16" to 72" OD (406 mm to 1829 mm) |
| Wall Thickness | 6.0 mm to 40 mm (up to 60 mm for piling applications) |
| Length | 6 m to 12.3 m standard; up to 18 m available |
Chemical Composition (Grade 50D)
*Note: BS 4360 Grade 50 is a structural steel grade. Subgrades include 50A, 50B, 50C, and 50D, with varying impact test requirements. Grade 50D has the most stringent low-temperature toughness.*
| Element | Maximum % | Notes |
|---|---|---|
| Carbon (C) | 0.20% | Low carbon for good weldability |
| Manganese (Mn) | 1.50% | Provides strength and hardenability |
| Silicon (Si) | 0.50% | Deoxidizer |
| Phosphorus (P) | 0.040% | Controlled for weldability |
| Sulfur (S) | 0.040% | Controlled for toughness |
| Vanadium (V) | 0.003-0.150% | Micro-alloying for grain refinement |
| Niobium (Nb) | 0.003-0.100% | Micro-alloying for strength |
Mechanical Properties
| Property | Grade 50 Value | Notes |
|---|---|---|
| Yield Strength (min) | 345-355 MPa (50-51 ksi) | At thickness ≤ 16mm |
| Tensile Strength (min) | 450-480 MPa (65-70 ksi) | Varies by subgrade |
| Elongation | 20-24% | Depends on thickness |
| Charpy Impact | 27 J at 0°C (Grade 50C/50D) | Grade 50D tested at -15°C or -20°C |
Grade 50 Subgrades Comparison
| Subgrade | Yield Strength (min) | Tensile Strength (min) | Impact Test Temperature | Typical Application |
|---|---|---|---|---|
| 50A | 345 MPa | 450 MPa | Not required | General structural, non-critical |
| 50B | 345 MPa | 450 MPa | Not specified | General structural |
| 50C | 345 MPa | 450 MPa | 27 J at 0°C | Outdoor structures in temperate climates |
| 50D | 345 MPa | 480 MPa | 27 J at -15°C to -20°C | Cold climates, demanding applications |
*Grade 50D offers the highest toughness, suitable for low-temperature and offshore applications.*
Dimensional Specifications
| Parameter | Range / Tolerance |
|---|---|
| Outside Diameter | 16" to 72" (406 mm to 1829 mm) |
| Wall Thickness | 6.0 mm to 40 mm (up to 60 mm for piling) |
| Diameter Tolerance | ±0.75% of specified OD (typical) |
| Wall Thickness Tolerance | +15% / -12.5% of nominal (typical) |
| Length | 6 m to 12.3 m standard; up to 18 m available |
Wall Thickness Availability by Diameter:
| OD (inch) | OD (mm) | Wall Thickness Range (mm) |
|---|---|---|
| 16" | 406 | 6.0 - 14.0 |
| 20" | 508 | 6.0 - 16.0 |
| 24" | 610 | 6.0 - 18.0 |
| 30" | 762 | 7.0 - 21.0 |
| 36" | 914 | 8.0 - 24.0 |
| 40" | 1016 | 8.0 - 26.0 |
| 48" | 1219 | 9.0 - 28.0 |
| 56" | 1422 | 10.0 - 29.0 |
| 60" | 1524 | 10.0 - 29.0 |
| 64" | 1626 | 10.0 - 30.0 |
| 72" | 1829 | 10.0 - 30.0 |
Source:
Testing & Inspection Requirements
| Test Type | Requirement | Notes |
|---|---|---|
| Chemical Analysis | Per heat lot | Verifies composition limits |
| Tensile Test | Per lot | Verifies yield and tensile strength |
| Flattening Test | Required | Checks ductility and weld integrity |
| Bend Test | Required | Verifies weld integrity |
| Charpy Impact Test | When specified | For low-temperature applications (27J at 0°C to -20°C) |
| Hydrostatic Test | Per project/standard | For pressure applications |
| NDT (Ultrasonic/X-ray) | Weld seam inspection | Standard practice for DSAW |
| Mill Test Certificate | EN 10204 Type 3.1B | Provided with full test results |
Common Applications
| Application | Description |
|---|---|
| High-Rise Building Construction | Columns, beams, trusses for tall structures |
| Bridge Engineering | Structural members, supports, major bridge components |
| Offshore Platforms | Marine structures, oil/gas platforms |
| Piling Foundations | Load-bearing piles for heavy structures |
| Heavy Engineering | Crane booms, excavator components, heavy machinery |
| Wind Turbine Towers | Large-diameter support structures |
| Low-Pressure Fluid Transmission | Water, gas, and oil pipelines |
| Infrastructure Projects | Tunnels, retaining walls, highway structures |
Modern Equivalent Standards
BS 4360 has been withdrawn and replaced by EN 10025. The direct modern equivalents of Grade 50 are:
| BS 4360 Grade | Modern EN Equivalent | Key Characteristics |
|---|---|---|
| 50A | S355JR | 27 J at +20°C |
| 50B | S355J0 | 27 J at 0°C |
| 50C | S355J2 | 27 J at -20°C |
| 50D | S355K2 | 40 J at -20°C (higher toughness) |
International Equivalents:
ASTM A572 Grade 50 (US standard)
EN 10025 S355JR/S355J2 (European standard)
DIN St52-3 (German standard, historical)
GB/T 1591 Q355B (Chinese standard)
Important Considerations
1. Standard Status
BS 4360 has been withdrawn and replaced by EN 10025. The direct modern equivalent of Grade 50 is S355JR/S355J2 (EN 10025-2). For new projects, specifying S355JR or S355J2 is recommended.
2. Grade 43 vs. Grade 50
| Grade | Yield Strength | Modern Equivalent |
|---|---|---|
| Grade 43 | ~275 MPa (40 ksi) | S275JR |
| Grade 50 | ~355 MPa (51 ksi) | S355JR / S355J2 |
Grade 50 offers approximately 29% higher yield strength than Grade 43.
3. Product Standard
While BS 4360 defines the material grade, the finished DSAW pipe product is typically manufactured to product standards such as:
EN 10219 (cold-formed welded structural hollow sections) – for structural applications
EN 10217 (welded tubes for pressure purposes) – for pressure applications
ASTM A252 (pipe piles) – for piling applications
4. Impact Properties by Subgrade
The Grade 50 designation includes several subgrades with different impact test requirements:
50A: No impact testing – general structural, indoor applications
50B: Limited impact requirements
50C: 27 J at 0°C – suitable for temperate outdoor climates
50D: 27 J at -15°C to -20°C – suitable for cold climates, offshore, and demanding applications
For applications requiring guaranteed low-temperature toughness, specify Grade 50C (0°C) or Grade 50D (-20°C).
5. Coating Options
DSAW pipe can be supplied with various coatings for corrosion protection:
FBE (Fusion Bonded Epoxy) – for buried pipelines
3LPE (3-layer polyethylene) – for buried applications
Coal Tar Epoxy – for marine environments
Varnish/Anti-rust oil – temporary protection
Bitumen coating – for buried service
Galvanizing – for outdoor applications
6. End Finishes
Plain ends – standard for most applications
Beveled ends – for field welding (30° bevel angle)
Threaded ends – for mechanical connections
7. Third-Party Inspection
Available inspection services include SGS, BV, Lloyds, TUV.
Summary
BS 4360 Grade 50 Double-Sided Submerged Arc Welded (DSAW) steel pipe is a high-strength product for large-diameter structural and demanding engineering applications. While the BS 4360 standard has been withdrawn, Grade 50 remains widely recognized, with its modern equivalent being EN 10025 S355JR/S355J2.
Key features:
Grade 50 offers minimum yield strength of approximately 355 MPa (51 ksi) – 29% higher than Grade 43
Subgrade options (50A, 50B, 50C, 50D) allow selection of appropriate impact toughness for the service environment
DSAW manufacturing produces pipes from 16" to 72" OD with wall thickness up to 40 mm (60 mm for piling)
Double-sided welding creates a single high-quality weld nugget
JCOE or UOE forming methods ensure precise dimensional accuracy
Cold expansion (up to 1.5%) may be applied, which can increase yield strength
Common applications include:
High-rise building construction and bridge engineering
Offshore platforms and marine structures
Heavy engineering and wind turbine towers
Piling foundations for heavy structures
Low-pressure fluid transmission (water, gas, oil)
When ordering, specify: BS 4360 Grade 50 [Subgrade: A/B/C/D] (or modern equivalent EN 10025 S355JR/S355J2), DSAW (Double-Sided Submerged Arc Welded), Size (OD x WT), Length, End Finish (plain/beveled), and Coating Requirements.
For new projects, EN 10025 S355JR/S355J2 is the recommended material specification. For applications requiring guaranteed low-temperature toughness, specify Grade 50C (0°C) or Grade 50D (-20°C).
