Sour service seamless pipe for H₂S-bearing oil and gas: standards, chemistry, mechanical properties and procurement notes.
In the oil and gas industry, sour service corrosion-resistant seamless pipe is a key material for the safe transport of sour (H₂S-bearing) hydrocarbons. API 5L X52NS / L360NS seamless pipe combines resistance to hydrogen sulphide corrosion with high strength, which makes it a preferred solution for high-sulphur oil and gas fields, offshore platforms and other demanding environments.
- API L360NS sour service seamless pipe / API X52NS sour service line pipe / X52NS corrosion-resistant seamless pipe
- Application: transport of oil and gas in sour drilling environments, and manufacture of pipe fittings
- Material / grade: X52NS / L360NS
- Size range: OD 48–765 mm, WT 3.5–120 mm
- Standards: API SPEC 5L, GB/T 9711
What kind of seamless steel pipe material is X52NS / L360NS?
X52NS / L360NS is a sour service seamless pipe under API 5L, developed for transporting oil and gas containing corrosive media such as hydrogen sulphide (H₂S) and carbon dioxide (CO₂). X52NS corresponds to API 5L PSL2: "X" denotes line pipe steel and "52" a minimum yield strength of 52 ksi (about 360 MPa). L360NS corresponds to the Chinese standard GB/T 9711, where "L" denotes line pipe and "360" a yield strength of 360 MPa. The suffix "NS" indicates sour service treatment (N for normalizing, S for sour resistance). The two designations have closely aligned chemical composition and mechanical properties, and both require HIC (hydrogen induced cracking) and SSC (sulphide stress cracking) test certification.
Standards and manufacturing process
Applicable standards
- API SPEC 5L (46th edition): defines the technical requirements for PSL2 pipe, including chemical composition control, mechanical testing and non-destructive examination.
- GB/T 9711: the equivalent Chinese standard, which governs the production process and performance requirements for L360NS.
Manufacturing process
- Steelmaking: 100-ton electric arc furnace (EAF), followed by LF refining and VD vacuum degassing to control steel cleanliness (sulphur ≤ 0.003%).
- Continuous casting: round billets are produced by continuous casting, with grain size controlled at grade 8.5 or finer.
- Rolling: thermo-mechanical controlled rolling (TMCP) on a precision cross-rolling mill refines the grain structure to improve strength and toughness.
- Heat treatment: normalizing at 920 °C with a cooling rate of 2–5 °C/s produces a ferrite plus pearlite structure and improves corrosion resistance.
- Inspection: each length undergoes hydrostatic testing, ultrasonic examination and HIC/SSC testing to confirm compliance with PSL2.
Chemical composition of API 5L X52NS / L360NS seamless pipe
| Element | Content (%) | Function |
|---|---|---|
| C | ≤0.16 | Carbon is tightly controlled to reduce weld cracking sensitivity and improve corrosion resistance. |
| Mn | ≤1.65 | Increases strength and toughness, working together with the other alloying elements. |
| P | ≤0.020 | Phosphorus is strictly limited to reduce the risk of intergranular corrosion. |
| S | ≤0.003 | Very low sulphur suppresses sulphide inclusions and improves HIC/SSC resistance. |
| V / Nb / Ti | ≤0.10 / ≤0.05 / ≤0.04 | Microalloying elements refine the grain structure and improve strength and ageing resistance. |
| CE (IIW) | ≤0.43 | Carbon equivalent control, to support weldability and crack resistance. |
Mechanical property requirements for API 5L X52NS / L360NS seamless pipe
| Property | Requirement | Notes |
|---|---|---|
| Yield strength | 360–530 MPa | Maintains structural stability under high-pressure transport. |
| Tensile strength | 460–760 MPa | Withstands sudden pressure surges and helps prevent rupture. |
| Elongation after fracture | ≥21% | Provides deformation capacity under complex geological conditions. |
| Sour service performance | HIC: CLR ≤15%, CSR ≤5%, CTR ≤1%; SSC: no cracking after 720 hours | Optimised chemistry and heat treatment provide resistance to hydrogen sulphide corrosion. |
| Impact energy | ≥80 J at −20 °C (PSL2) | Retains toughness at low temperature to avoid brittle fracture. |
Main applications and project examples
High-sulphur oil and gas transmission
- Example: a Middle East oil field used X52NS seamless pipe for a sour gas transmission pipeline. With HIC/SSC test certification, the line ran for five years without corrosion failure in an environment where H₂S concentration reached 150 ppm.
Offshore platform oil lines
- Example: an offshore platform in the South China Sea used L360NS seamless pipe together with a corrosion-resistant coating, standing up to both seawater attack and high-pressure hydrocarbon transport.
Corrosive media in the chemical industry
- Example: a chemical plant used X52NS pipe to carry CO₂-bearing acidic solution. Corrosion resistance was significantly better than plain carbon steel and service life was extended by more than three times.
Certification and procurement notes
Certification
- API Monogram: confirms the product meets PSL2 requirements of API SPEC 5L, 46th edition.
- ISO 9001 quality management certification: supports a standardised and traceable production process.
- NACE MR0175 / ISO 15156 (optional): additional corrosion-resistance certification for severe sour environments.
Procurement notes
- Confirm the product specification level: specify PSL2 so that chemical composition, mechanical properties and NDE meet the higher requirements.
- Verify sour service performance: request HIC/SSC test reports and confirm the CLR, CSR and CTR results.
- Check delivery condition: normalized (N) or thermo-mechanically rolled (M) is preferred over as-rolled (AR).
- Check dimensional tolerances: OD tolerance ±1% and wall thickness tolerance ±12.5%, so the pipe matches the piping system.
Working with PAC STEEL
As a supplier of API 5L X52NS / L360NS seamless pipe, PAC STEEL supports customers with:
Related products: API 5L seamless line pipe
- Certified quality: API Monogram, ISO 9001 and other certifications support traceable product quality.
- Full size range: OD 48–762 mm and WT 3.5–120 mm to suit different project requirements.
- Customised service: chemistry optimisation, corrosion-resistant coatings and other solutions based on service conditions.
- Technical support: assistance from material selection through to installation guidance.
Contact PAC STEEL for technical documentation and a quotation for sour service corrosion-resistant seamless pipe.