Pipeline systems involve linear segments that connect the point of origin for the product to discrete facilities that process the product, drive it toward delivery or storage, and meter its volume and regulate its pressure at delivery. Pipelines sit ‘midstream’ in their value chain, with the Segment titled Components and Loads illustrating this value chain and the role of pipelines.

Components and Loads.

This Segment deals with the steps in making the linear segments of the pipeline system. A companion Segment addresses the production of double submerged-arc welded (DSAW) pipe, although aspects such as hot rolling, the mill hydrotest, and cold expansion that are included here are not covered in that Segment.

Line pipe for oil and gas transmission service is produced to minimum standards presented in regard to two product specification levels (PSL). PSL1 is a loose standard quality for line pipe, whereas PSL2 is more stringent. PSL2 pipe includes additional testing requirements, tighter requirements on chemical composition, different ceiling limits on mechanical properties, and require Charpy impact testing, non-destructive inspection of seamless products, certification to Supplemental Requirement (SR) 15, and traceability throughout the production process. PSL2 is generally a mandated requirement the details for which are presented in the now harmonized API 5L and ISO 3183 specifications [1]. Many operators supplement these requirements with other documents, such as a manufacturing process specification.

Details supported by this Segment begin with steel making leading to billets for seamless (SMLS) pipe production, or as slabs for hot-rolling into plate or coiled skelp for use in making welded pipe. The transformation from billets or slabs into pipe is considered next in regard to the making of SMLS pipes, or the forming of plate or skelp into a thin-walled cylinder or ‘can’, which is then closed axially to make welded pipe using a longitudinal (long) seam that runs straight or helically along length of the can. Videos and documents available via the Internet follow below that illustrate each of the steps involved for both SMLS and welded pipe.

Overview of Steel and Pipe Making

An overview of steel production through casting which leads to its large long and flat product forms for use in pipe mills (i.e., billets, and slabs) can be accessed through the link:

For those interested in further details the chapter titled Primary Mill Fabrication in Metals Fabrication – Understanding the Basics (edited by F.C. Campbell, ASM, 2013) is a good resource. As of this writing this chapter is available online as a ‘sample chapter’, which can be accessed through the link:

A general introduction to pipe making can be found at the link:

Making Seamless Pipe

The transformation from reheated billet to finished SMLS pipe can be accessed through the link:

The first of these is an animation, whereas the second illustrates mill production. As some aspects in the mill process cannot be easily accessed, it is best to view the animation first. The links that follow all deal with the making of line pipe using a longitudinal welded seam.

Hot-Rolling to Make Plate and Skelp for Welded Pipe

As the plate and skelp used in making welded pipe comes from the hot rolling of reheated slabs, this process is illustrated first by way of a two-part video. The first part of this video deals with the process from the slab through coiled strip. The second part, which begins about 6:24, presents the process focused on plate production. This video can be accessed through the link:

Making Helical and Straight-Seamed Submerged-Arc Welded Pipe

As is apparent in the DSAW QR Segment noted above, submerged-arc welded (SAW) pipe is produced either with a straight-seam (often denoted LSAW pipe) or with a helical-seam (often denoted HSAW pipe, or SSAW in reference to the spiral seam). Details concerning the SAW process as well as the production of LSAW and HSAW pipe can be found by scanning the QR code embedded above.

Making Straight-Seamed ERW Pipe

While SAW pipe can be made using either a straight or helical seam, as becomes evident in the videos that follow the ERW process is practical only in straight-seam production. Two videos follow that illustrate making straight-seamed ERW pipe. The first of these is an animation, whereas the second illustrates mill production. As some aspects in the mill process cannot be easily accessed, it is best to view the animation first.

Mill Hydrotest

A mill hydrotest to a minimum pressure (90% of SMYS) for a minimum time (10 seconds) is a required step in the production of PSL2 line pipe. Videos of pipe production often include a snippet that covers this aspect. An animated video of this process can be found through the following link:

Cold Expansion

Not all PSL2 pipe includes cold expansion. When it is used many pipe mills make use of a mechanical expansion process. The link that follows includes a snippet illustrating aspects of mechanical cold expansion over the interval from about 2:30 through about 4:00:


  1. Anon., “Petroleum and natural gas industries – Steel pipe for pipeline transportation systems” ISO 3183 / Specification for Line Pipe, API 5L