OIL & GAS PIPES
There are two main types of oil and gas pipes: seamless and welded. Seamless pipes are the preferred choice for high pressure and critical applications, as they guarantee robustness and superior mechanical properties. In this article, we define seamless, ERW, ERW-HFI, LSAW pipes and show some useful videos to understand their fascinating manufacturing processes.
Seamless pipes are one of the most common types of oil and gas pipes. They are manufactured by drawing a solid billet (in carbon, alloy, stainless or nickel alloy steel) through a piercing rod that creates a circular hollow section. Seamless pipes are superior to welded pipes as they are manufactured from a monolithic block of steel (a steel billet), with intrinsic mechanical strength, and do not require welds. Seamless pipes are the most common type of pipes used within the petrochemical industry (line pipes and process piping).
Seamless pipes have a higher price per ton than erw and saw pipes, due to their complex production process and the high investments needed to set up manufacturing (most mills have vertically integrated plants, which produce both the billet and the finished pipe).
For specific sizes and specifications (diameter/ thickness/materials), the number of manufacturers is small, the competition is low, and the price per tonne is, therefore, higher and not aligned with the actual fabrication costs (a good example are the chrome-alloy seamless pipe for power generation according to the ASTM A335 P91 specification).
The dimensions of US standard seamless pipes are defined by ASME B36.10 (carbon and alloy steel pipes), by ASME B36.19 (stainless and nickel-alloy steel pipes) and by API 5L (line pipes for oil and gas transmission and distribution). The dimensions of European seamless pipes are defined by the EN 10220 and EN 1127 specifications (respectively, carbon/alloy and stainless steels and higher grades). Seamless pipes for upstream operations (“OCTG” casing and tubing pipes, aka Oil Country Tubular Goods) are specified by the API 5CT norm.
Seamless pipes are available in ferrous and non-ferrous materials (more details about the typical materials for seamless pipes are in this article) and in a size range between 1/8 and 24 inches (in some cases up to 28 or 32 inches, by using pipe-expanders). Seamless pipes sizes are shown in this article.
Seamless pipes from 1/8 to 6 inch. are manufactured with the so-called “plug mill process” or the “extrusion process” (used for smaller diameters), whereas the “mandrel mill process” is used for larger diameters.
Seamless Pipe Manufacturing Process (source: Tenaris)
ERW pipes (“electric resistance welding”) are oil and gas pipes manufactured by welding steel coils longitudinally. The high-frequency induction technology (HFI) is the most widespread process in use for these economical pipes: an induction coil is applied on the outer surface of the tube and generates a current which joins the two sides of the coil very tightly.
They HFI welding technology is superior to other techniques and ERW-HFI are common pipes for oil and gas/petrochemical application. ERW-HFI pipes are a good alternative to seamless pipes for specific applications and size ranges, and indeed they sometimes are alternative options.
The dimensions of welded pipes are defined by ASME B36.10 (carbon and alloy steel pipes) and by ASME B36.19 (stainless and nickel-alloy steel pipes), and by EN 10220 and EN 1127 (European welded pipes dimensions). Electric resistance welding pipes are available in most material grades, being carbon and stainless steel the most common, and in a size range between 1/2 to 20 inches.
The ERW manufacturing process (source: Tenaris)
Submerged arc welded (SAW) pipes are manufactured by bending and welding steel plates. SAW pipes are oil and gas pipes used for hydrocarbons transmission and distribution (the recurring specification for this type of pipes is the API 5L). LSAW pipes are more expensive than ERW’s in the overlapping size range, i.e.16 to 24 inches, and are the only option for bore sizes above 28 inches (at least for petrochemical applications).
SAW pipes are available in the LSAW and DSAW types (single or double longitudinal submerged arc welding). SSAW/HSAW pipes (spirally welded pipes) are instead used for low pressure and non-critical application as water transmission and distribution (not for oil & gas). LSAW pipes are available in any material grades, and in dimensions between 16 through 80 inches (and above). Carbon steel and stainless steel are the most common materials for this large bore size pipes.
LSAW pipes manufacturing process (source: Corinth Pipeworks)
Seamless, ERW and LSAW pipes are available in carbon steel (ASTM A53, ASTM A106, ASTM A333 for low temperature, API 5L), alloy steel (ASTM A335 in grades from P1 to P91 and beyond), stainless steel (ASTM A312, including duplex and super-duplex, ASTM A790/A928), super austenitic stainless steel, nickel-alloys and non ferrous materials.