Purpose of each standard

• ASTM A106 – seamless carbon steel pipe for high-temperature service in refineries, power plants and process plants. Grades A, B and C.
• ASTM A53 – seamless and welded black and galvanised pipe for pressure and mechanical use – water, steam, gas and air lines, and structural uses. Types F (furnace butt welded), E (ERW) and S (seamless); Grades A and B.
• API 5L – line pipe for oil, gas and water pipelines, seamless or welded, in Grade B and X42 to X80 and above, at product specification levels PSL1 and PSL2.

Comparison table

Chemistry and steelmaking

A106 requires a minimum silicon content of 0.10%, which means the steel is killed – deoxidised – giving a uniform, sound structure suitable for high-temperature service where graphitisation and ageing must be avoided. A53 and API 5L PSL1 do not require minimum silicon. API 5L PSL2 adds tighter limits on carbon, manganese and impurities, and a maximum carbon equivalent, to ensure good field weldability of pipelines. Our ASTM A106 Grade B pipes page gives the full A106 chemistry.

Testing differences

All three require tensile tests and hydrostatic or non-destructive testing of each length. A106 adds bend or flattening tests. A53 welded pipe requires flattening tests on the weld. API 5L PSL2 adds Charpy impact testing, maximum yield and tensile strengths, a maximum yield-to-tensile ratio and full non-destructive testing of the weld seam on welded pipe; sour-service PSL2 pipe adds hydrogen-induced cracking and sulphide stress cracking tests. These extra controls are why pipelines usually specify API 5L PSL2.

Triple certification

Because their Grade B requirements overlap, mills often produce seamless pipe that meets ASTM A106 Grade B, ASTM A53 Grade B and API 5L Grade B (PSL1) at the same time, and mark it with all three. One stock of triple-certified pipe can then supply plant piping, utility lines and short pipelines. The certificate must show compliance with each standard, including A106's silicon minimum and the test requirements of each. Triple certification does not cover API 5L PSL2 unless the pipe also meets the PSL2 requirements.

Which should you specify?

Use A106 for process and steam piping in plants, especially above about 350 °C and in refinery service. Use A53 for water, air, gas and steam lines at moderate temperatures, sprinkler and firewater systems, and structural pipe; Type E (ERW) is economical where seamless is not needed, and galvanised A53 is common for water. Use API 5L for oil, gas and water pipelines and gathering lines, choosing PSL2 and the grade to suit the design pressure and the project specification.

Temperature limits

A106 Grade B is listed in ASME B31.3 and the boiler code for service at elevated temperatures, with allowable stresses up to high temperatures, and is the usual choice for steam and hot hydrocarbon lines. A53 is also listed, but welded A53 carries a weld joint factor, and A53 is generally used at more moderate temperatures. API 5L is designed for pipeline service at near-ambient temperatures; when it is used in plants, the piping specification sets the temperature range. For low-temperature service below about −29 °C, none of the three is used without impact testing – ASTM A333 Grade 6 pipe is specified instead.

Marking and certification

Each standard requires the pipe to be marked with the specification, grade, size, wall thickness, heat number and the mill's identification, and for API 5L also the PSL and, for mills licensed by API, the licence marking. Triple-certified pipe carries all three specifications in its marking and on the mill test certificate. When ordering, state the standards and grades required so that the certificate covers each one.

Fittings and flanges to match

A106 and A53 pipe are used with ASTM A234 WPB butt-weld fittings and ASTM A105 flanges. API 5L pipelines in higher grades use high-yield fittings to MSS SP-75 (WPHY grades) and flanges to ASTM A694 or MSS SP-44, matched to the pipe grade so that the joint is as strong as the pipe. For sour pipelines, all components are supplied to NACE MR0175 / ISO 15156 on request.

Common mistakes

Ordering A53 Type E when seamless pipe is required, or API 5L PSL1 when the project needs PSL2, are frequent errors. Another is assuming that any "Grade B" pipe meets A106 – A53 and API 5L pipe without the A106 silicon minimum and test requirements cannot be certified to A106. Always state the full designation: standard, type or PSL, grade, size and wall.

Products

We supply all three – see ASTM A106 Grade B pipes, API 5L line pipes, carbon steel seamless pipes and carbon steel ERW pipes. More guides are on the technical resources page.