What are the dimensional and wall thickness specifications for A106 A106M steel pipe?

ASTM A106/A106M is the standard specification for seamless carbon steel pipe used in high-temperature service. Engineers who specify pipe for refineries, power plants, boiler systems, and process piping need a clear answer to one practical question: what are the actual dimensional and wall-thickness limits you can order? This guide walks through the size range, the ASME B36.10 schedule table, the manufacturing routes, the chemistry and mechanical properties by grade, and the dimensional tolerances that govern acceptance. Where it helps procurement, we link directly to the ASTM A106/A106M seamless steel pipe product page and to related pipeline works in the EZ Steel catalog.

Size Range Covered by the Standard

A106/A106M covers seamless carbon steel pipe from NPS 1/8 to NPS 48, which equals DN 6 to DN 1200. Wall thickness follows the nominal values given in ASME B36.10. The standard also allows other dimensions, provided the pipe still meets every other requirement, so non-standard OD or heavier walls are possible when the project calls for big diameter steel pipe used in transmission mains or high-pressure process headers.

Pipe ordered under A106 must be suitable for bending, flanging, similar forming operations, and welding. When the steel is to be welded, the purchaser and the manufacturer are expected to agree on a procedure that matches the grade of steel and the intended service.

Grades and How They Differ

A106 defines three grades: A, B, and C. Strength rises from A to C, while the chemistry stays within a tight carbon-manganese envelope. Grade B is by far the most common because it balances strength, weldability, and cost for refinery, petrochemical, and power-plant service.

Chemical Composition (ladle analysis, %)

The sum of chromium, copper, molybdenum, nickel, and vanadium shall not exceed 1%. The maximum carbon equivalent (CE) is 0.5, calculated as CE = C + Mn/6 + (Cr + Mo + V)/5 + (Ni + Cu)/15. For each 0.01% reduction below the specified carbon maximum, manganese may rise by 0.06% above the maximum, up to 1.35% for Grade A and 1.65% for Grades B and C.

Mechanical Properties

A separate elongation table applies for strip specimens taken from larger pipe, but the 20% minimum in 2 in. is the headline number used in procurement documents.

Wall Thickness and Schedule (ASME B36.10)

The schedule table below lists the nominal wall thickness, in inches, for the most-requested NPS sizes. The same data drive the metric equivalents (mm) shown in most project specifications. Values for sizes larger than NPS 26 are taken from the ASME B36.10 light-wall section, where only a few schedules are standardized.

Schedules 10 and 20 are standardized only for NPS 14 and larger, and double-extra-strong (XXS) is only standardized up to NPS 12. Heavier walls (SCH 140, SCH 160, XXS) are used for high-pressure boiler tubing and feed-water lines, while SCH 40 and SCH 80 cover the majority of process piping.

Manufacture: Hot-Finished vs. Cold-Drawn

A106 pipe is made by two routes:

• Hot-finished seamless — used unless otherwise specified for NPS 2 [DN 50] and larger. Optional for smaller sizes. Surface carries an oxide scale from hot working; tolerance on OD and wall is wider, but the pipe has excellent ductility and is the standard choice for high-temperature headers.
• Cold-drawn seamless — tighter dimensional and surface finish. Used for smaller sizes, precision applications, hydraulic lines, and where the project calls for closer ID/OD control. Cold-drawn pipe must be heat-treated after the final draw at 1200 °F [650 °C] or higher.

For service in heat exchangers and surface condensers, the cold-drawn A179/A179M is often the better fit for the tube side, while A106A/B pipes are used on the shell side and in feed lines. See the related ASTM A179/A179M seamless low-carbon pipe for heat exchangers and condensers for those applications.

Heat Treatment

Heat-finished seamless A106 pipe is typically delivered in the as-rolled or normalized condition and does not require additional heat treatment. When heat treatment is specified, it shall be performed at 1200 °F [650 °C] or higher. Cold-drawn pipe must be heat-treated after the final draw at the same minimum temperature. The resulting structure meets the mechanical property table above without further processing.

Dimensional Tolerances

Outside Diameter (hot-finished seamless, in./mm)

Cold-drawn pipe follows the tighter OD table in the A106/A106M standard: ±0.40 mm for OD ≤ 48.3 mm, and ±1% for OD ≥ 60.3 mm.

Wall Thickness, Mass, and Length

• Wall thickness tolerance: the minimum wall at any point shall not be more than 12.5% under the specified nominal wall.
• Mass tolerance: −3.5% / +10% per length.
• Single random lengths: 16 to 22 ft [4.8 to 6.7 m] with ≥ 35 ft [10.7 m] average; up to 5% may be shorter than 22 ft.
• Double random lengths: minimum average ≥ 35 ft [10.7 m], each piece ≥ 22 ft [6.7 m].

Pipe-End Preparation

For NPS 1 1/2 [DN 40] and smaller, the ends are plain-end square cut or plain-end beveled. For NPS 2 [DN 50] and larger, walls up to and including extra-strong are plain-end beveled; walls heavier than extra-strong are plain-end square cut. The standard bevel angle is 30°–35° with a root face of 0.8 to 2.4 mm, ready for field welding.

Hydrostatic Test and Nondestructive Examination

Each pipe is hydrostatically tested, or the manufacturer performs a nondestructive electrical test, or both. The marking on the pipe tells you which combination was used.

The hydrostatic test pressure is calculated by P = 2St / D, where S is the allowable pipe-wall stress, t is the nominal wall thickness, and D is the specified outside diameter. The pressure is held for at least 5 seconds with no leakage. When NDE is used instead of, or in addition to, the hydro test, the inspection follows ASTM E213, E309, or E570. Ultrasonic testing is the most common NDE route for high-temperature A106 pipe used in refineries and power plants.

Bending, Flattening, and Forming

Pipes NPS 2 [DN 50] and smaller must pass a 90° bend around a mandrel whose diameter is 12 times the pipe OD, with no cracking on the outside of the bend. For larger pipe where the diameter-to-thickness ratio is 7.0 or less, a guided bend test is performed: a specimen is bent 180° at room temperature around a 1 in. [25 mm] inside-diameter mandrel. A flattening test is not required by default; it is added only when specified in the purchase order under Supplementary Requirement S3.

Where A106/A106M Is Used

A106 Grade B is the workhorse pipe for high-temperature process piping. The most common applications include:

• Refinery process piping, hydrocracker and catalytic reformer headers, and hot oil lines.
• Power-plant main steam, reheat, and feed-water piping, including high-pressure boiler tubing runs.
• Petrochemical plant piping for ethylene, ammonia, and methanol units.
• Boiler feedwater and condensate return lines, where heat exchanger tube material is selected separately for the tube side.
• Oil and gas transmission, processing, and distribution systems, often paired with API 5L line pipe for cross-country pipelines.

Stainless steel A312/A269 or alloy A335 pipe is chosen when the service demands higher corrosion resistance or higher temperature. For lower-temperature water service, A53 or A106 Grade A may be specified. Project supply packages typically include the matching carbon, stainless, and alloy steel flanges and the gaskets, stud bolts, and nuts needed for the joints.

Equivalent or Near-Equivalent Standards

A106/SA106 maps closely to several other national and regional standards. The following are widely accepted equivalents:

• EN 10216-2 (P235GH, P265GH) — non-alloy steel tubes with elevated temperature properties.
• JIS G3456 (STPT370 / STPT410 / STPT480) — equivalent to Grade A, B, C respectively.
• DIN 17175 (St35.8 / St45.8) — German elevated-temperature tube standard.
• GB/T 5310 — Chinese standard for high-pressure boiler tubes.
• BS 3602 (HFS / CFS 360, 410, 460) — British carbon steel pipe for high-temperature service.

These equivalents are useful when a project source is dual-certified, or when a specific market requires a national standard.

Procurement Checklist

When ordering A106/A106M pipe, capture the following in the purchase order to avoid mismatches at the warehouse or on site:

1. Grade (A, B, or C) and the matching ASME designation (SA-106).
2. Size: NPS / DN and the schedule (SCH 40, 80, 160, XXS, or a custom wall).
3. Manufacture: hot-finished or cold-drawn.
4. Length type: single random, double random, or cut to length with a tolerance.
5. Test method: hydrostatic, NDE (UT / ET), or both, with marking on the pipe.
6. End finish: plain-end square cut, plain-end beveled, or threaded and coupled.
7. Heat treatment: as-rolled, normalized, or quenched and tempered.
8. Supplementary requirements: S1 (product analysis), S2 (tensile at elevated temperature), S3 (flattening test), and so on.
9. Mill test certificate: EN 10204 3.1 or 3.2, with traceability to heat number.
10. Surface protection: black, varnish, FBE, 3LPE, 3LPP, or galvanized, plus end caps and packaging.

Practical Tips for Selection

• If the design code is ASME B31.1 (Power Piping) or B31.3 (Process Piping), use the allowable stress table for A106 in the code. Grade B is the typical default.
• For bends and fittings matched to A106 pipe, specify butt-weld (BW) fittings in the same grade and schedule, per ASME B16.9. Socket-weld (SW) fittings are restricted to small-bore, non-corrosive service.
• For services above 800 °F [425 °C] or where creep is a design driver, switch to an alloy like A335 P11 or P22. A106 is limited to lower temperatures.
• For big diameter steel pipe in transmission mains, confirm the project allows hot-expanded or cold-expanded pipe; some specs only accept hot-finished.
• Always request a sample MTR before bulk shipment, and confirm that the heat number, grade, and dimensional tolerances match the purchase order.

Frequently Asked Questions

Is A106 Grade B the same as API 5L Grade B?

No. A106 is a seamless pipe standard for high-temperature service, while API 5L is a line-pipe standard that may be seamless or welded and is used for oil and gas transmission. The two have different chemistry, mechanical properties, and testing requirements. For pipeline applications, A106 may be used for plant piping, while API 5L PSL1 or PSL2 is used for the long-distance line pipe.

Can A106 pipe be galvanized?

Yes, A106 can be hot-dip galvanized. The galvanizing bath temperature is well below the 1200 °F [650 °C] heat-treatment threshold, so the mechanical properties are not affected. Galvanized A106 is common in low-pressure water service, fire protection, and structural applications.

What is the difference between A106 and A53?

A53 covers both seamless and welded pipe and is used for general low- and medium-temperature service, including steam, water, and air. A106 is exclusively seamless and is designed for high-temperature service. The chemistry of A106 has tighter limits on phosphorus and sulfur, and the mechanical properties are higher than A53 Grade B in most cases.

Does A106 require a flattening test?

By default, no. A flattening test is only required if Supplementary Requirement S3 is invoked in the purchase order. In practice, most project specs include the bend test for small sizes and rely on the hydrostatic or NDE for larger pipe.

Summary

ASTM A106/A106M defines a seamless carbon steel pipe with three grades (A, B, C) covering NPS 1/8 to NPS 48. Wall thickness follows ASME B36.10, with the common schedules being SCH 40, 80, 120, 160, and XXS for sizes up to NPS 12, and a smaller set of standardized schedules for NPS 14 and larger. Tight tolerances govern the outside diameter, wall thickness, and mass, and every pipe is delivered with a mill test certificate that ties back to the heat number. For procurement, the key questions are grade, size, schedule, manufacture route, end finish, test method, and supplementary requirements. With those locked in, the order will line up with the standard, with the matching pipe fittings, and with the project specification.