Steel Pipe / Line Pipe

Seamless or welded: how the line divides

Pipe in this line is either seamless or welded, and the choice is normally settled by diameter and by what the line is designed to do.

Seamless pipe is pierced from a solid billet and has no seam, which is why it is specified where the pipe will be bent, threaded or used at temperature.

Welded pipe is formed from strip or plate and seam welded. The three welded routes follow the diameter: ERW to about 24 in (610 mm), LSAW from 16 in to 60 in (406–1,524 mm), and SSAW from 8 in to 100 in (219–2,540 mm) where the diameter is large and the pressure is not.

Most families in this line come in more than one form; the size each form is supplied in is in the table below.

What this line covers, and which page carries it

Steel pipe in this line is grouped by material and by standard, and the enquiry usually lands on one of six families. The family decides the grade system, the test regime and the coating, so it is worth fixing before the size. If the service is inside a wellbore rather than on the surface, it belongs to the OCTG line instead.

For the choice between a straight longitudinal seam and a helical seam, see LSAW vs SSAW pipe.

Tube for boilers and heat exchangers sits at the end of this line: boiler and heat exchanger tube covers ASTM A179, A192, A210 and A213 in small diameters and thin walls.

What we supply, by family and size

The table below is the range the line is supplied in. A size outside it is quoted per project against the mill’s rolling programme rather than assumed.

Coating, end preparation and documents are separate decisions from the size; the order they are settled in is below.

Sour service and low temperature are separate decisions

Neither of these is a coating question or a wall question, and both are decided before the grade is chosen.

Sour service is decided by the H₂S partial pressure together with pH, chloride content, temperature and total pressure, against NACE MR0175 / ISO 15156. It rules out the plain line pipe grades unless the material and the weld are qualified for the service — higher strength grades carry hardness and welding limits that have to be respected. Where the assessment permits a carbon steel, the requirement is stated on the order rather than added at the mill.

Low temperature is decided by the design metal temperature, and it selects the grade rather than the wall: ASTM A333 grades are impact tested at the temperature the design calls for, and A333 is not a coating or a wall thickness. Specifying a thicker wall of a grade that was never impact tested does not satisfy the requirement.

The inputs for the sour assessment, and what each one changes, are set out on the sour service page. The low temperature grades and their test temperatures are on the ASTM A333 page.

How the specification is fixed, in the order that avoids a re-quote

The order of the questions matters. The service condition comes first because it can remove a whole grade family — sour service and low temperature both do — and everything after it is arithmetic on the design.

1. The service condition. What the line carries, whether it is buried or above ground, the design temperature, and whether H₂S is present. The two binary questions — sour service and impact testing to a design metal temperature — are set out above, because they remove whole grade families before the standard is chosen.
2. The standard and grade. API 5L grade and PSL for line pipe, or ASTM A106, A333, A335 or A312 for plant piping. The grade comes from the design, not from what is in stock.
3. The wall. The design pressure and diameter give the wall, and the wall then has to be checked against the available weight and against the bending the line will see during installation.
4. The manufacturing route. Seamless or welded, and if welded, ERW, LSAW or SSAW — the definitions and the diameter split are above. The route follows the diameter and the duty, and a welded route brings a weld that has to be qualified where the service is sour or low temperature.
5. The coating or surface treatment. 3PE and FBE for buried line pipe, cement mortar lining for water, galvanizing for exposed structures and services. The coating is a separate decision from the grade and from the wall.
6. The inspection and the documents. PSL2 adds non-destructive examination, an impact test and tighter dimensional tolerances on top of PSL1, and the certificate type is stated on the order.

Where line pipe orders go wrong

Frequently asked questions

What to state on the enquiry

Send these, and the first quotation comes back without a second round of questions:

• The service condition — whether the line is sour, and whether it has to be impact tested to a design metal temperature.
• Standard and grade — API 5L grade and PSL, or the ASTM A106, A333, A335 or A312 grade.
• Outside diameter and wall thickness, or schedule.
• Manufacturing route — seamless, ERW, LSAW or SSAW.
• Length and end finish.
• Coating or surface treatment.
• Quantity and destination port.

For a single-page profile of the China export scope and accountabilities, see steel pipe supplier in China.

Related reading: 3PE vs FBE coating, steel pipe vs tube and CRA clad and lined pipe. API 5L line pipe for Venezuela.

API 5L pipe supplier scope

Mejor Steel supplies API 5L line pipe as a China export package: seamless and welded, grades B to X80 (ERW to X70, LSAW and SSAW for the larger diameters), PSL1 and PSL2, with the wall, length, end finish, coating and mill test certificate fixed on the same enquiry. The grade and the PSL are confirmed against the line design, not assumed from the diameter alone.