Seamless steel pipes for oil&gas applications

Why seamless pipe is the standard in oil&gas

Seamless steel pipes are produced by hot rolling a pierced billet using the Mannesmann process with a mandrel mill or pilger mill. The absence of a weld seam eliminates the heat-affected zone (ZTA) and longitudinal discontinuities, ensuring isotropic mechanical properties and high resistance to internal pressure: decisive characteristics for flowlines, gathering lines, process piping, manifolds and OCTG.

Grades and reference standards

• API 5L / ISO 3183: pipes for transmission lines, specification levels PSL1 and PSL2, grades from B to X80 (X42, X52, X60, X65, X70). PSL2 imposes tighter limits on chemical composition, carbon equivalent (CEIIW, Pcm), Charpy V toughness and NDT inspection.
• ASTM A106 Gr.B: carbon-manganese steel for high temperatures, typically for refinery piping and process plants according to ASME B31.3.
• ASTM A333 Gr.6: normalised steel for low-temperature service with a Charpy V impact test at –45 °C, suitable for liquefied gases, moderate cryogenic plants and Arctic climates.
• ASTM A53 Gr.B and ASTM A335 (P5, P9, P11, P22) for medium- and high-temperature applications with Cr-Mo alloy steels.

Sour service and H₂S resistance

In the presence of hydrogen sulphide (H₂S), the main risks are sulphide stress cracking (SSC) and HIC (Hydrogen Induced Cracking). Pipes for sour service must comply with NACE MR0175 / ISO 15156, with tests according to NACE TM0177 (SSC) and TM0284 (HIC), a maximum hardness of 22 HRC (250 HV) and controlled sulphur and phosphorus contents, typically S ≤ 0,003%.

Heat treatments and inspection

The delivery condition may be as rolled, normalised (N) or quenched and tempered (Q&T). The normalising cycle refines the ferritic grain, improving yield strength and toughness. Inspection includes:

• ultrasonic testing (UT) for longitudinal and transverse defects and laminations;
• magnetic particle testing (MT) at the ends;
• hydrostatic testing at the mill;
• tensile, Charpy V, bend and hardness tests;
• PMI (Positive Material Identification) on alloy materials.

Documentation and traceability

The material must be accompanied by an EN 10204 3.1 or 3.2 certificate (with the involvement of a third-party body such as Bureau Veritas, TÜV or SGS), a heat number, indelible marking complying with the standard and, for projects in the EU, compliance with the PED Directive 2014/68/UE.

How to choose the right pipe

Selection depends on design pressure, minimum and maximum temperature, fluid (dry gas, crude oil, formation water, CO₂), corrosion allowance, wall thickness (schedule SCH 40, SCH 80, SCH XS, SCH XXS) and nominal diameter (NPS/DN). Request a quotation with the complete specification to receive availability, delivery times and certifications.