Imagine that an engineer is specifying large-diameter LSAW steel pipe for a high-voltage industrial system. He stops on a piece of paper and it says: NPS 12 SCH XS. This key specification determines the safety and efficiency of the system-in order to conduct accurate stress analysis, the engineer need accurate steel pipe size, verified wall thickness data and reliable formulas to calculate maximum allowable working pressure (MAWP)
As an authoritative technical reference, this paper provides a complete XS pipe data table, and gradually guides the application of these values to the calculations of large diameter welded pipes (such as LSAW steel pipe and SSAW pipes) Whether designing pipelines or verifying infrastructure, it has unveiled the mystery of schedule XS for data-driven decision-making.

Schedule XS (abbreviation of “Extra Strong”) is a standardized wall thickness name defined in ASME B36.10m. It originated from early pipeline manufacturing, and it classifies pipelines with thickness greater than SCH 40 to provide enhanced pressure resistance and structural integrity. Unlike any labels, Schedule XS is universal, ensuring consistency across manufacturers.
Schedule XS is applicable to all major pipeline types-seamless, LSAW steel pipe (longitudinal submerged arc welding) and SSAW steel pipes (spiral submerged arc welding). This consistency simplifies material procurement and quality control for large-scale projects such as oil and gas pipelines or industrial boilers, which usually use LSAW and SSAW steel pipes.
By understanding this key difference, we can avoid costly mistakes.
· NPS 1/8 “to NPS 8”: Schedule XS and SCH 80 share identical wall thicknesses (often used interchangeably here).
· NPS 10 “and larger: SCH 80 thickness increases with diameter, while Schedule XS remains fixed at 0.500 inches (12.7 mm).
This “anomaly” stems from manufacturing constraints in history. For modern projects that use large diameter LSAW steel pipe or SSAW pipes, replacing these names will lead to over-design (and cost) or the risk of damaging safety.
All data are in accordance with ASME B 36.10 m standard, which is the global benchmark for steel pipe size. The following table includes the key specifications of XS steel pipes-from small diameters to large sizes used in LSAW steel pipe and SSAW steel pipes-including outside diameter (OD), wall thickness (WT) and weight per foot.
| NPS (in) | Outside Diameter(in) | Wall Thickness (in) | Weight(lb/ft) | Notes |
| 1/8” | 0.405 | 0.095 (Same as SCH 80) | 0.18 | — |
| 1/4” | 0.540 | 0.119 (Same as SCH 80) | 0.31 | — |
| 3/8” | 0.675 | 0.126 (Same as SCH 80) | 0.43 | — |
| 1/2” | 0.840 | 0.147 (Same as SCH 80) | 0.62 | — |
| 3/4” | 1.050 | 0.188 (Same as SCH 80) | 1.03 | — |
| 1” | 1.315 | 0.219 (Same as SCH 80) | 1.47 | — |
| 1-1/4” | 1.660 | 0.250 (Same as SCH 80) | 2.27 | — |
| 1-1/2” | 1.900 | 0.281 (Same as SCH 80) | 3.00 | — |
| 2” | 2.375 | 0.343 (Same as SCH 80) | 4.77 | — |
| 2-1/2” | 2.875 | 0.375 (Same as SCH 80) | 6.41 | — |
| 3” | 3.500 | 0.437 (Same as SCH 80) | 9.11 | — |
| 4” | 4.500 | 0.531 (Same as SCH 80) | 14.98 | — |
| 5” | 5.563 | 0.625 (Same as SCH 80) | 22.85 | — |
| 6” | 6.625 | 0.432 (Same as SCH 80) | 28.57 | — |
| 8” | 8.625 | 0.500 (Same as SCH 80) | 43.39 | — |
| 10” | 10.750 | 0.500 (SCH 80 = 0.594) | 54.74 | Common in SSAW pipes |
| 12” | 12.750 | 0.500 (SCH 80 = 0.688) | 65.42 | Popular for LSAW steel pipe |
| 14” | 14.000 | 0.500 (SCH 80 = 0.750) | 72.09 | — |
| 16” | 16.000 | 0.500 (SCH 80 = 0.843) | 82.85 | — |
| 18” | 18.000 | 0.500 (SCH 80 = 0.937) | 93.61 | — |
| 20” | 20.000 | 0.500 (SCH 80 = 1.031) | 104.37 | Common in large-diameter SSAW pipes |
| 24” | 24.000 | 0.500 (SCH 80 = 1.218) | 125.89 | Frequently used in LSAW steel pipe projects |
· The dimensions of steel pipe meet the global compatibility requirements of ASME b36.10m.
· For NPS 10 “+(typical LSAW/SSAW sizes), the fixed thickness of 0.500 inch in XS plan simplifies the planning of large-scale projects.
· Weight values (excluding accessories/coatings) supports logistics and load calculations.
In order to ensure safety of XS pipeline, especially LSAW steel pipe and SSAW pipeline in high-pressure application, engineers rely on Barlow formula, which is the industry standard for MAWP calculations.
The formula for MAWP (psi) is
P = (2 * S * t) / D
In which:
· P = maximum allowable working pressure (MAWP).
· S = allowable stress in ASME b31.3 (psi, yield strength-safety factor).
· T = wall thickness of schedule XS (inches, from data sheet).
· D = outside diameter of the pipe (inches, from data sheet).
1.Allowable stress(S): ASME B 31.3 provides numerical values (e.g., ASTM A 106 grams. B = 20,000 psi; Api gravity 5 l x 65 = ~ 30,000 pounds per square inch, 100 degrees F).
2. Wall Thickness (t): Use nominal Schedule XS thickness (e.g., NPS 12 “) is 0.500 inches.
3. Outer diameter (d): fixed according to NPS size (ASME B 36.10 m) for consistent calculations.
MAWP of NPS 12 “LSAW steel pipe is calculated (attached table XS, API 5 L X 65, s = 30,000 psi).
D = 12.750 inches (NPS 12 inches, schedule XS).
T = 0.500 inches (from data sheet).
S = 30,000 psi (in accordance with ASME B 31.3, API 5 L X 65).
p = (2 * 30,000 * 0.500)/12.750.
Step 3: Calculate the Result
30,000 ÷ 12.750 ≈ 2,352 psi.
This LSAW steel pipe can work safely under the pressure of about 2,352 psi, which is very important for verifying the pressure requirements of the project.
Suitable for NPS 20 ” SSAW pipe (Schedule XS, ASTM A106 Gr. B, S = 20,000 psi):
p = (2 * 20,000 * 0.500)/20.000 = 1,000 psi.
Schedule XS is a standardized, reliable specification for high-pressure systems. Its fixed large diameter and thickness (NPS 10 “+) makes it cost-effective for LSAW steel pipe and SSAW steel pipes, while its consistency with ASME B 36.10 m ensures global compatibility.
The Schedule XS vs. SCH 80 distinction is non-negotiable for large pipes—substitution risks safety or unnecessary costs. Using the data sheet and Barlow’s Formula with accurate steel pipe dimensions lets engineers confidently specify Schedule XS for demanding applications.
Success relies on high-quality, ASME-compliant Schedule XS pipes. We specialize in producing LSAW steel pipe and SSAW steel pipes, which are tailored according to the pressure, size and material requirements of your project. Our engineers will verify calculations results and ensure that they meet the safety objectives.
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