Pipelines – Industry's Steel Network

What do water, petroleum and natural gas have in common? All three substances must be transported economically across very great distances. As a rule, the overland transport of these media takes place in pipelines - steel pipes, sometimes thousands of kilometers long. Depending on the application, these large-diameter pipes place very complex demands on steel as the material in use. Salzgitter Flachstahl has been developing and producing modern pipe steels for industry for several decades.

Submerged welding of outer weld seam

Pipes for pipelines must meet the strictest requirements. Extreme ambient conditions, such as the harsh Arctic or desert climates are only one factor. High operating pressures of up to 200 bar for natural gas, often over a number of decades, are called for in view of the profitability studies for  pipeline projects. Consequently, a high level of structural durability for the material and its joints – the welded seams - is essential. Very good weldability in the pipe manufacture and during the laying in the field is a minimum requirement here, and zero faults in the weld seam is the demanded reality.
Excellent wear resistance against abrasion is a further important requirement that the steel material must fulfill.  Abrasion arises, for example, from a multitude of small grains of sand which are carried along when oil or natural gas is extracted from the stone and which then remain in the medium.

Resistance to acid gas is becoming increasingly important. The background: oil and gas wells with a high content of hydrogen sulfide are more and more frequently being tapped and exploited. These media are likewise highly corrosive, even if at the atomic level and undetectable with the naked eye.

HIC resistance (HIC – hydrogen induced cracking) is verified on a batch-by-batch basis with special tests. Test pieces are placed into an acidic medium for a period of several days and then tested for cracks after this corrosive action. If the material is flawless, the next manufacturing step follows – delivery to the pipe manufacturing area.

After forming and welding the outside of the tube is grit blasted and protected against corrosion

The characteristics and chemical composition of steels for large-diameter pipes are described in a number of standards, such as EN 10028, EN 10208 and API 5L. Two uses of fine-grain structural steels according to EN 10028 are for simple pressure lines and in structural steel construction. They exhibit good weldability and resistance to brittle fracture at minimum yield strengths of 275 – 460 MPa. Special types are delivered for stricter requirements with regard to low application temperatures down to -20° C or higher operating temperatures up to 400° C.

Salzgitter Flachstahl supplies only the hot rolled wide strip for manufacturing large-diameter pipes. The EN 10208-2 and API 5L standards, however, stipulate the levels to be reached on the pipe. As a result, the mechanical characteristics must be coordinated with the order using the pipe diameter, welding method and other parameters. The large-diameter pipe grade (up to X70 according to API 5L or up to L485MB according to EN 10208) from Salzgitter Flachstahl has been tested and approved for use in pipelines by the Technische Überwachungsverein (TÜV) (including DIN 2470, Part 2). Hot-rolled strip thickness of up to 24 mm and widths up to 2,000 mm can be delivered upon agreement. The following table provides an overview of the products for this area. Application areas are usually pipelines for transporting petroleum and natural gas.