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ASME B36.10M-2018 — Welded and Seamless Wrought Steel Pipe
📏 ASME B36.10M-2018, Welded and Seamless Wrought Steel Pipe, is the fundamental dimensional standard of the piping industry. It specifies nominal sizes, wall-thickness series, and weights (masses) per unit length for welded and seamless wrought steel pipe. The Standard is maintained by the ASME B32 Committee, and its history goes back to March 1927, when the American Standards Association authorized a sectional committee on standardization of dimensions and material of wrought steel and wrought iron pipe and tubing; the first meeting was held in Pittsburgh on May 18, 1928. The first issue was designated an American “tentative” Standard in November 1935 and converted to an American Standard on April 28, 1939. The dimensional table was originally designed to cover power piping requirements where strength to resist internal pressure governs wall selection, and was later expanded to include sizes and thicknesses used in other industries, including the sizes and weights of API Standards 5L and 5LX. Table 2-1 of the Standard gives complete dimensions and masses for each nominal size from NPS 1/8 through NPS 80 across all wall-thickness series.
💡 The Schedule numbers (e.g., Sch 40, Sch 80) were originally intended to establish a system of size/wall combinations with an approximately uniform relationship equal to 1,000 times the P/S expression of the modified Barlow formula, but the resulting numbers departed so far from common practice that they were adopted strictly as a convenient designation system for ordering.
1. Scope and Standard Structure 📌
The body of the Standard comprises: Section 1, Scope; Section 2, Size; Section 3, Materials; Section 4, Wall Thickness; Section 5, Weights/Masses; Section 6, Permissible Variations; Section 7, Pipe Threads; Section 8, Wall-Thickness Designations; and Section 9, Wall-Thickness Selection. The heart of the document is Table 2-1, which lists dimensions and weights (masses) of welded and seamless wrought steel pipe for each nominal size and wall-thickness series. The Standard states clearly that in all cases the designer must base wall selection on the rules and allowable stresses set by the code governing the particular construction; the table is a dimensional and ordering designation system, not a design code.
⚠️ B36.10M is not a design specification: it tells you the dimensions and mass of “this outside diameter with that wall thickness,” but not whether that wall can carry the pressure. Pressure-wall calculations must go back to the ASME B31 piping codes or the governing design code.
2. Nominal Sizes and Wall-Thickness Series 🔧
Sizes are designated by Nominal Pipe Size (NPS), covering NPS 1/8 through NPS 80. Table 2-1 lists, for each nominal size, the wall-thickness series including the traditional names Standard, Extra-Strong (Extra Heavy), and Double Extra-Strong, plus the Schedule-number series (Sch 5s, 10s, 20, 30, 40, 60, 80, 100, 120, 140, 160, etc.).
| NPS | Outside Dia. (in.) | Common Wall Series | Typical Application |
|---|---|---|---|
| 1/8 | 0.405 | Sch 40, 80 | Instrument lines, small process lines |
| 1/2 | 0.840 | Sch 40, 80, 160 | General process and utility |
| 1 | 1.315 | Sch 40, 80, 160 | General process piping |
| 2 | 2.375 | Sch 40, 80, 160, XXS | Process and utility piping |
| 4 | 4.500 | Sch 40, 80, 120, 160 | Main process lines in plants |
| 8 | 8.625 | Sch 20, 40, 80, 120 | Large plant piping |
| 12 | 12.75 | Sch 20, 40, 60, 80 | Transmission and plant lines |
| 24 | 24.00 | Sch 10, 20, 40, 80 | Large-diameter transmission lines |
| 48 | 48.00 | Sch 20, 40, etc. | Water and long-distance lines |
| 80 | 80.00 | Sch 20, 40, etc. | Very large special projects |
3. Permissible Variations and Pipe Threads 📏
Section 6 covers permissible variations in dimensions (outside diameter, wall thickness, and mass), and Section 7 addresses pipe threads: where threaded pipe is required, the threads should be machined to the dimensions and tolerances of the applicable pipe-thread standard (e.g., ASME B1.20.1 for NPT). Wall-thickness variations are typically expressed as a percentage of nominal wall; outside-diameter variation depends on size and on the manufacturing method (seamless or welded). The required variation class must be stated at purchase, because variations directly affect the minimum wall used in pressure calculations.
| Item | Description | Engineering Impact |
|---|---|---|
| Outside diameter variation | Graded by seamless/welded method and size | Affects flange and fitting fit |
| Wall thickness variation | Given as % of nominal wall | Determines the minimum wall for pressure design |
| Mass per unit length | Theoretical mass from nominal wall in Table 2-1 | Drives material take-off and lifting design |
| Pipe threads | Per B1.20.1 and similar thread standards | Seal reliability of threaded joints |
⚠️ Wall selection must distinguish “nominal wall” from “minimum wall”: manufacturing variations remove material, so pressure calculations and corrosion allowance should be based on the minimum wall, or you may end up short of strength.
4. Engineering Practice Essentials 🛠️
- 🔍 Selection workflow: determine the required minimum wall from media, design temperature, and design pressure per the governing code → pick the wall-thickness series in Table 2-1 not less than that value → order by Schedule number → state OD, wall, length, and manufacturing method.
- 🔧 Size consistency: a given NPS has a unique outside diameter; wall changes only affect the inside diameter. Flange, valve, and fitting interface dimensions are therefore stable — one of the greatest engineering values of the B36.10M system.
- 📊 Mass take-off: material mass is calculated from the unit-length masses in Table 2-1; total line weight and freight estimates for long pipelines rest on these values.
- 📋 Seamless vs. welded: seamless and welded pipe of the same nominal size share the OD, but variations, testing, and preferred pressure classes differ; always state the manufacturing method and the applicable ASTM/API material specification when ordering.
- ✅ Heavy walls: some of the larger heavy-wall sections are beyond seamless mill production capability and must be obtained from forged and bored billets or other sources — confirm manufacturability at purchase.
🚨 Do not equate “Standard” wall with “Sch 40” without checking size: the two coincide for small sizes (e.g., NPS 1/2) but diverge at larger sizes. Always write both the NPS and the Schedule number (or traditional name) in design and order documents to avoid wrong material.
5. Frequently Asked Questions ❓
❓ Q: What is the difference between B36.10M and B36.19M?
A: B36.10M covers welded and seamless wrought steel (carbon and alloy) pipe, while B36.19M covers stainless steel pipe, mainly providing the “s” suffix wall series such as Sch 5s, 10s, 40s, and 80s. The two share the same OD system but differ in wall series.
A: B36.10M covers welded and seamless wrought steel (carbon and alloy) pipe, while B36.19M covers stainless steel pipe, mainly providing the “s” suffix wall series such as Sch 5s, 10s, 40s, and 80s. The two share the same OD system but differ in wall series.
❓ Q: Does the Schedule number decide pressure capability?
A: No. The Schedule number is only a wall-designation system for ordering. Pressure capability depends on material, actual minimum wall, and allowable stress at design temperature, computed to the governing code.
A: No. The Schedule number is only a wall-designation system for ordering. Pressure capability depends on material, actual minimum wall, and allowable stress at design temperature, computed to the governing code.
❓ Q: How does NPS relate to the outside diameter?
A: At NPS 12 and below, the OD is larger than the nominal size (e.g., NPS 2 has an OD of 2.375 in.); at NPS 14 and above, the OD numerically equals the nominal size (e.g., NPS 24 has an OD of 24.00 in.).
A: At NPS 12 and below, the OD is larger than the nominal size (e.g., NPS 2 has an OD of 2.375 in.); at NPS 14 and above, the OD numerically equals the nominal size (e.g., NPS 24 has an OD of 24.00 in.).
🔍 Q: Why do some walls go by both “Standard” and “Sch 40”?
A: The traditional names (Standard, Extra-Strong, Double Extra-Strong) and Schedule numbers coexist; they correspond for many sizes (e.g., NPS 1/2 Standard = Sch 40) but not all, so an explicit specification is the only safe basis for ordering.
A: The traditional names (Standard, Extra-Strong, Double Extra-Strong) and Schedule numbers coexist; they correspond for many sizes (e.g., NPS 1/2 Standard = Sch 40) but not all, so an explicit specification is the only safe basis for ordering.
