1. Scope
This standard covers factory-made wrought high-strength carbon and low-alloy steel buttwelding fittings in sizes NPS 1 through NPS 24 for use in high-pressure gas and oil transmission and distribution systems — including pipelines, compressor stations, metering and regulating stations, and mainline. The fittings are designed for service in ASME B31.4 (liquid pipeline transport) and B31.8 (gas transmission/distribution) piping systems.
Edition: MSS SP-75-2025 | Size Range: NPS 1–24 | Grades: WPHY 42, 46, 52, 56, 60, 65, 70 | Heat Treatment: Normalized (N) for WPHY 42–60; Quenched and Tempered (QT) for WPHY 65–70 | Material Spec: ASME SA-860 (ASTM A860/A860M) | Key Change from 2014: Scope expanded to include carbon and low-alloy steel (not limited to ferritic steel); substantially revised from previous edition with API task group input
2. WPHY Grade Overview — Mechanical Properties
| Grade |
Min Yield (MPa) |
Min Tensile (MPa) |
Max YS/T S Ratio |
Heat Treatment |
API 5L Equivalent |
| WPHY 42 |
290 |
415 |
0.84 |
Normalized (N) |
X42 |
| WPHY 46 |
317 |
435 |
0.84 |
Normalized (N) |
X46 |
| WPHY 52 |
359 |
455 |
0.85 |
Normalized (N) |
X52 |
| WPHY 56 |
386 |
490 |
0.85 |
Normalized (N) |
X56 |
| WPHY 60 |
414 |
515 |
0.88 |
Normalized (N) |
X60 |
| WPHY 65 |
448 |
530 |
0.90 |
QT |
X65 |
| WPHY 70 |
483 |
565 |
0.93 |
QT |
X70 |
3. Chemical Composition (Max, % by Heat Analysis)
| Element |
WPHY 42–52 |
WPHY 56–60 |
WPHY 65 |
WPHY 70 |
| C |
0.23 |
0.22 |
0.18 |
0.18 |
| Mn |
0.95–1.35 |
0.95–1.40 |
0.95–1.50 |
0.95–1.60 |
| P |
0.030 |
0.030 |
0.030 |
0.030 |
| S |
0.010 |
0.010 |
0.010 |
0.010 |
| Si |
0.15–0.40 |
0.15–0.40 |
0.15–0.40 |
0.15–0.40 |
| Ni |
0.40 |
0.40 |
0.50 |
0.50 |
| Cr |
0.25 |
0.25 |
0.40 |
0.40 |
| Mo |
0.10 |
0.10 |
0.25 |
0.25 |
| V |
0.06 |
0.08 |
0.08 |
0.08 |
| Nb |
0.04 |
0.04 |
0.04 |
0.04 |
| Ti |
0.04 |
0.04 |
0.04 |
0.04 |
| CE (IIW) |
0.43 |
0.45 |
0.43 |
0.43 |
4. Fitting Types and Available Sizes
| Fitting Type |
Radius |
Size Range (NPS) |
| 90° Elbow |
1.5D (LR) |
1 – 24 |
| 45° Elbow |
1.5D (LR) |
1 – 24 |
| Equal Tee |
— |
1 – 24 |
| Reducing Tee |
— |
1-1/4 – 24 |
| Concentric Reducer |
— |
1 – 24 |
| Eccentric Reducer |
— |
1 – 24 |
| Buttweld Cap |
— |
1 – 24 |
5. Heat Treatment Requirements
| Grade |
Required Heat Treatment |
Typical Process Temperature |
| WPHY 42 |
Normalized (N) |
900–960°C, air cooled |
| WPHY 46 |
Normalized (N) |
900–960°C, air cooled |
| WPHY 52 |
Normalized (N) |
900–960°C, air cooled |
| WPHY 56 |
Normalized (N) |
900–960°C, air cooled |
| WPHY 60 |
Normalized (N) |
900–960°C, air cooled |
| WPHY 65 |
Quenched and Tempered (QT) |
900–940°C water quench + 550–650°C temper |
| WPHY 70 |
Quenched and Tempered (QT) |
900–940°C water quench + 550–650°C temper |
6. Mechanical Testing Requirements
| Test |
Requirement |
| Tensile test (body) |
Yield strength, tensile strength, elongation — per grade table above |
| Bend test |
Free-bend test to 180° without cracking on WPHY 42–52; guided-bend test for higher grades |
| Charpy V-notch impact |
Min avg 20 J (15 ft·lbf) at design temp; individual ≥ 16 J (12 ft·lbf) |
| Hydrostatic test |
1.5× minimum allowable pressure from B31.4 or B31.8 hoop stress formula |
| Wall thickness UT |
Mandatory for WPHY 65/70; recommended for WPHY 42–60 |
| PMI (Positive Material ID) |
Strongly recommended; confirms chemistry compliance with the heat analysis requirements |
7. MSS SP-75 vs ASME B16.9 vs ASME B16.28 — Comparison
| Parameter |
MSS SP-75 |
ASME B16.9 |
ASME B16.28 |
| Size range |
NPS 1–24 |
NPS 1/2–48 |
NPS 1/2–24 (SR) |
| Yield strength |
290–565 MPa (WPHY 42–70) |
240 MPa (WPB) |
240 MPa (WPB) |
| Dimensional standard |
SP-75 own tables |
B16.9 tables |
B16.28 tables |
| Fitting weight |
Shorter/smaller than B16.9 |
Standard |
SR — compact |
| Material heat treatment |
N or QT mandatory |
Per SA-234 (WPB annealed) |
Per SA-234 |
| Charpy CVN required |
Yes — mandatory |
No mandatory CVN |
No mandatory CVN |
| Application code |
B31.4 / B31.8 |
B31.3 |
B31.3 |
8. Related Standards
| Standard |
Title |
| ASME SA-860 |
Wrought High-Strength Carbon and Low-Alloy Steel Fittings (material specification for SP-75) |
| ASTM A860/A860M |
Wrought High-Strength Carbon and Low-Alloy Steel Fittings (ASTM equivalent of SA-860) |
| API 5L |
Line Pipe (X42–X80, matching pipe grades for SP-75 fittings) |
| ASME B31.4 |
Pipeline Transportation Systems for Liquids |
| ASME B31.8 |
Gas Transmission and Distribution Piping Systems |
| ASME B16.9 |
Factory-Made Wrought Buttwelding Fittings (carbon/alloy) |
| ASME B16.25 |
Buttwelding Ends |
| MSS SP-25 |
Standard Marking System for Valves, Fittings, Flanges and Unions |
9. How to Order (Per MSS SP-75)
| Order Element |
Specification |
Example |
| Standard |
MSS SP-75 |
SP-75 |
| Fitting type |
Elbow/Tee/Reducer/Cap |
LR 90° Elbow |
| Size |
NPS |
12 |
| WPHY grade |
WPHY 42 / 46 / 52 / 56 / 60 / 65 / 70 |
WPHY 60 |
| Wall thickness / Schedule |
Per project pipeline spec |
Per API 5L X60 pipe wall |
| Ends |
Beveled per B16.25 |
Beveled |
| Charpy test temperature |
Design temperature (e.g., –30°C) |
–30°C, 20 J avg |
| NDE requirements |
UT, MPI, RT per code |
100% UT body wall |
| Material test report |
EN 10204 3.1 MTC |
3.1 MTC + CVN results |
10. FAQ — Frequently Asked Questions
| Question |
Answer |
| Can WPHY 70 fittings be used in sour service? |
WPHY 70 fittings can be used in sour service per NACE MR0175/ISO 15156 when the material is specifically qualified and the H₂S partial pressure, pH, and temperature are within the acceptable region defined in Part 2 of ISO 15156. The fitting must be manufactured from a heat with documented chemistry and heat treatment meeting the sour service acceptance criteria. WPHY 65/70 grades in the QT condition have specific hardness limits (≤ 235 HBW for sour service) and may require additional HIC (Hydrogen-Induced Cracking) testing for wet H₂S environments. |
| Why is Charpy V-notch testing mandatory for SP-75 fittings? |
Pipeline fittings are exposed to plastic deformation during the forming process (elbows are bent, tees are extruded or formed). This forming can reduce notch toughness — particularly in the heavily worked extrados of formed elbows. The Charpy test verifies that the fitting retains adequate toughness to resist brittle fracture during hydrostatic testing (when the system is pressurized to 1.25–1.5× design pressure at ambient temperature) and during operation, especially in cold climates or when the pipeline transports fluids at low temperatures. |
| Can WPHY fittings be welded to API 5L X70 pipe? |
Yes — WPHY fittings are designed to be buttwelded to matching API 5L line pipe using compatible welding procedures. WPHY 60 fittings are typically matched with API 5L X60 pipe; WPHY 70 with X70 pipe. The filler metal should be compatible with both the fitting and pipe chemistry. For WPHY grades with QT heat treatment, the heat-affected zone (HAZ) adjacent to the weld may experience tempering of the QT microstructure — a post-weld heat treatment (PWHT) may be required per the governing code (B31.4/B31.8) depending on the thickness and the code's PWHT exemption tables. |
| What is the difference between WPHY 65 QT and WPHY 70 QT in practice? |
WPHY 65 and WPHY 70 are both QT grades but differ in yield strength (448 MPa vs 483 MPa minimum). WPHY 70 uses a slightly modified chemistry with higher carbon equivalent (CE) to achieve the higher strength. The higher CE makes WPHY 70 more sensitive to PWHT — it may require PWHT at thinner sections than WPHY 65 for equivalent Code relief. WPHY 70 is typically used in high-pressure offshore gas pipelines (ASME B31.8) where the wall thickness allows for QT processing without cracking. WPHY 65 is more common for onshore liquid pipelines (ASME B31.4) where the slightly lower strength is offset by better weldability. |
| Why are SP-75 fittings shorter than B16.9 fittings? |
SP-75 fittings are dimensionally optimized for pipeline applications where minimizing weight and material cost is critical across hundreds or thousands of fittings. Pipeline operators routinely compare fitting costs per kilometre of pipeline — shorter fittings mean lower material weight, lower freight costs, and in some cases, reduced installation labour. The mechanical integrity is maintained because the WPHY material's higher yield strength (vs WPB) means the fitting body can be lighter while still meeting the pressure design requirements. However, this means SP-75 and B16.9 fittings are not interchangeable in the same piping run. |
