What is Anti-Hydrogen Sulfide Corrosion Pipe Steel?

In the petrochemical industry, hydrogen sulfide (H2S) corrosion is prevalent and highly hazardous. By analyzing the mechanism of H2S corrosion, this article introduces the forms of corrosion caused by wet H2S, including hydrogen blistering, hydrogen-induced cracking (HIC), sulfide stress corrosion cracking (SSCC), and stress-assisted hydrogen-induced cracking. It highlights the relationship between the mass concentration of H2S in liquid phase, pH, temperature, and other factors with the aforementioned corrosion phenomena. Through practical case studies, the basic requirements for selecting pipe materials are analyzed from a design perspective, discussing the selection criteria for different situations. Researching anti-H2S corrosion pipe materials is crucial for extending the lifespan of pipelines, preventing accidents, and improving economic efficiency.

Oil and natural gas, as essential energy sources for national economic development, are increasingly recognized worldwide. Currently, the transportation of oil and natural gas resources in China mainly relies on pipelines, which are typically spiral welded steel pipes. Due to the complex terrain crossed by pipelines, the environment varies both spatially and temporally, leading to erosion by various media. Acidic media, in particular, cause severe corrosion to pipelines. Standards adopted include GB/T 4157-2006, NACE TM0177-2005, ASTM G39-1999, ISO 7539-2-1989, and GB/T 15970.2-2000. Testing methods include:

  • Method A: Standard tensile test
  • Method B: Bending test
  • Method C: Ring-type test
  • Method D: Cantilever beam test (4-point bending method)

Evaluation results focus on compliance (presence of EC cracks, whether fractured).

Oil and Natural Gas as Key Energy Sources

Oil and natural gas are critical energy sources for national economic development and are widely recognized worldwide. Currently, the transportation of oil and natural gas resources in China mainly relies on pipelines, typically spiral welded steel pipes. Due to the complex terrain crossed by pipelines, the environment varies both spatially and temporally, leading to erosion by various media. Acidic media, in particular, cause severe corrosion to pipelines.

Hydrogen sulfide (H2S) is one of the most corrosive harmful media. The concentration of H2S in China’s oil and natural gas products is relatively high, causing significant H2S corrosion. This necessitates higher requirements for the anti-H2S corrosion performance of pipelines. With the large-scale development of high-sulfur gas fields like the Luojiazhai gas field, it is imperative to research anti-H2S corrosion pipe materials.

Researching anti-H2S corrosion pipe materials is crucial for extending the lifespan of pipelines, preventing accidents, and improving economic efficiency.

Principles for Selecting Anti-H2S Corrosion Pipe Materials

For sulfur-containing oil and gas pipelines, potential metal loss corrosion, hydrogen-induced cracking (HIC), and sulfide stress corrosion cracking (SSCC) must be considered during material selection. Russian experts believe that the greatest danger in pipelines exposed to H2S is not general corrosion (metal loss corrosion) but cracking associated with hydrogen permeation (SSCC). Therefore, the anti-stress corrosion performance of pipe materials is particularly important in pipelines containing H2S. To prevent H2S stress corrosion, the “NACE MR-0175” standard recommends that the hardness limit of pipes in acidic environments should not exceed 248 HV500 or 22 HRC. Reducing the content of impurities such as oxygen and sulfur in the steel can increase its resistance to sulfide stress corrosion.

In Canada, the Grizzly Valley pipeline system, which spans over 1,770 km, uses three diameters and wall thicknesses: Ø273 mm × 5.2 mm, Ø508 mm × 9.5 mm, and Ø610 mm × 11.4 mm. All pipelines comply with CSA-Z245.1 Grade 52 (359) and specify clear requirements for the chemical composition of steel used for transporting sulfur-rich dry gas. Carbon equivalent (CE) should not exceed 0.45%, determined by the following formula:

Additionally, the maximum Rockwell hardness (HRC) of the steel pipe is set at 20 HRC, and the maximum Vickers hardness (HV) is 238.

Texas has strict regulations for pipelines transporting natural gas with H2S concentrations exceeding 0.01%. To ensure the anti-crack characteristics of the material, Charpy V-notch impact tests are required for all welds, and residual stresses must be eliminated. Two international standards are commonly used to evaluate the anti-stress corrosion performance of pipe materials: the American NACE standard and the British BP standard.

Types of Anti-H2S Corrosion Pipe Materials

From the perspective of the development trend of natural gas pipelines, the following two types of pipes show promising prospects: low-cost, corrosion-resistant, and high-hardness special alloy steel with good weldability and anti-sulfur stress cracking, and synthetic fiberglass pipes.

Special Alloy Steels
HDR Duplex Stainless Steel

HDR is an ultra-low-carbon, high-chromium (H), duplex (D), corrosion-resistant (R) stainless steel, consisting of approximately 50% austenite and 50% ferrite. It combines the toughness of austenitic stainless steel with the stress corrosion cracking resistance of ferritic stainless steel, offering high mechanical properties, good weldability, and corrosion resistance suitable for acidic environments. The surface of HDR forms a dense protective film rich in chromium, nickel, molybdenum, and nitrogen, effectively preventing ion corrosion.

18-8 Type Stainless Steel

The 18-8 type stainless steel, such as AISI 304, is susceptible to intergranular corrosion and pitting near the weld due to the precipitation of chromium compounds. To mitigate this, solid solution annealing, limiting carbon content, and using appropriate welding rods are recommended. Adding trace elements like titanium and niobium can enhance corrosion resistance, e.g., 1Cr18Ni9Ti, widely used in gas fields.

Synthetic Fiberglass Pipes
PE Pipes

PE pipes are made from polyethylene resin with necessary additives and are extruded continuously. They are resistant to various chemical media except strong oxidizers and have a long service life, low friction, and reliable connections. These features make them suitable for transporting sulfur-containing oil and gas.

Glass Fiber Reinforced Composite Pipes

These pipes combine the high-pressure resistance of heat-resistant and corrosion-resistant PVC liners with the strength and rigidity of glass fiber and the impact resistance and aging resistance of high-density polyethylene outer layers. They are lightweight, corrosion-resistant, and easy to install, making them ideal for oil and gas applications.

Steel-Plastic Reinforced Composite Pipes

These pipes are reinforced with different materials and processes, such as steel wire mesh, steel plate mesh, and woven steel wire.

  • Steel Wire Mesh Reinforced Plastic Composite Pipes: Consist of a welded steel wire mesh skeleton and high-density polyethylene plastic. They offer high strength, low thermal expansion, and UV resistance.
  • Steel Plate Mesh Reinforced Plastic Composite Pipes: Use perforated steel tape as the reinforcement, combined with high-density polyethylene. They have similar properties to steel wire mesh reinforced pipes.
  • Woven Steel Wire Reinforced Plastic Composite Pipes: Use woven steel wire as reinforcement, providing good bonding with inner and outer layers. The working pressure depends on the number of layers, typically around 1.6 MPa, with cost advantages for large-diameter pipes.

Overall, alloy steels perform well and are widely used but currently do not meet industrial scale requirements. Synthetic fiberglass pipes have broader prospects due to their high strength, good flexibility, corrosion resistance, and low cost.

Conclusion

For sulfur-containing oil and gas pipelines, the presence of H2S leads to corrosion and degradation of the material’s physical, chemical, and mechanical properties, resulting in stress corrosion cracking and hydrogen-induced cracking, compromising the safety and lifespan of the pipelines. Therefore, when selecting materials, the anti-stress corrosion performance of pipe materials should be prioritized, learning from developed countries and adhering to international standards. China should strengthen research and testing of anti-H2S corrosion materials to develop new, applicable anti-H2S corrosion pipe materials.

Anti-sulfur steel pipes are suitable for acidic natural gas environments containing H2S (up to 30 g/m³). The manufacturing materials prevent sulfide cracking and hydrogen-induced cracking. According to “NACE MR0175,” the raw material hardness should not exceed 22 HRC, with a nickel content not exceeding 1%. After hot rolling, annealing, normalizing, and tempering, the materials can be selected. For A105 material, the hardness after heat treatment should not exceed 187 HBW, and for A234 material, it should not exceed 197 HBW. Domestic 20# steel corresponds to the A234 grade of American standards and meets anti-sulfur requirements after heat treatment.

Anti-H2S Corrosion Oil Casing

Anti-H2S corrosion special thread oil casing is used in environments containing H2S acid corrosion and ensures gas-tight sealing during oil and gas production. The pipe body material is a unique chromium-molybdenum steel with high hardenability and tempering stability, capable of obtaining fine and uniform tempered sorbite at certain temperatures. Through micro-adjustment of the composition and targeted heat treatment for different steel grades, the hardness and strength meet the requirements of the corresponding grades while demonstrating excellent resistance to SSCC. The oil casing connectors use custom-designed gas-tight thread types suitable for various complex and harsh conditions. The company’s anti-H2S stress corrosion special thread oil casing has passed rigorous evaluations by domestic authoritative institutions and is widely used in major oil fields. The C110 grade CBS3 casing has met the stringent evaluation requirements of the ISO 13679 standard.

Common Anti-H2S Stress Corrosion Grades:

  • CB80S, CB80SS, C90, CB90S, CB90SS, T95, CB95S, CB95SS, C110, CB110S, CB110SS
  • “S” indicates general anti-sulfur; “SS” indicates high anti-sulfur

Oil Casing Connector Types:

  • CBS1: Gas-tight special thread (oil and casing)
  • CBS2: Gas-tight special thread (oil and casing)
  • CBS3: Gas-tight special thread (oil and casing)
  • CBSJ: Economical low-pressure seal special thread (oil and casing)
  • CB-NUFJ: Direct-connect gas-tight special thread (oil and casing)
  • EU-HT/BC-HT: High-torque top-seal special thread (oil and casing)

Standards (Partial):

  • API Spec 5CT: Tubing and casing specification
  • ANSI/NACE MR0175/ISO 15156: Materials for oil and gas production in H2S environments
  • ANSI/NACE TM0177: Laboratory evaluation of metal resistance to sulfide stress cracking and stress corrosion cracking in H2S environments
  • API Spec 5B: Tubing, casing, and line pipe threading, measurement, and inspection specification
  • ISO 13679/GB/T 21267: Petroleum and natural gas industry tubing and casing thread connection test procedure

Physical and Chemical Properties:

Grade Name Yield Strength (MPa) Tensile Strength (MPa) Elongation (%) Impact Toughness Hardness
80 CB80S 552 655 655 Calculated by API 5CT formula 23
CB80SS
90 C90 621 724 689 Per API 5CT C90 requirement 25.4
CB90S
CB90SS
95 T95 655 758 724 Per API 5CT T95 requirement 25.4
CB95S
CB95SS
110 CB110S 758 862 793 Per API 5CT C110 requirement 30
CB110SS/C110

Corrosion Performance:

Grade Corrosion Resistance Requirement
C90 H2S stress corrosion test (SSC)
T95 H2S stress corrosion test (SSC)
CB110S H2S stress corrosion test (SSC)
CB80S H2S stress corrosion test (SSC)
CB90S H2S stress corrosion test (SSC)
CB95S H2S stress corrosion test (SSC)
C110 H2S stress corrosion test (SSC)
CB80SS H2S stress corrosion test (SSC)
CB90SS H2S stress corrosion test (SSC)
CB95SS H2S stress corrosion test (SSC)
C90 H2S stress corrosion test (SSC)
T95 H2S stress corrosion test (SSC)

Connector Performance:

Connector Type Internal Pressure Resistance Tensile Efficiency Compression Efficiency Applicable Well Conditions
CBS1 Equal to pipe body 100% pipe body 60% pipe body Less demanding well conditions, shallow and medium-depth oil wells
CBS2 100% pipe body 60% pipe body Demanding well conditions, medium and deep oil wells
CBS3 100% pipe body 60% pipe body More demanding well conditions, deep and ultra-deep wells, horizontal wells
CBS3C 100% pipe body 100% pipe body
CBSJ 100% pipe body 60% pipe body Low-pressure gas seal wells, ordinary horizontal wells, large-displacement wells
CB-NUFJ 45%~66% pipe body 45%~66% pipe body Repair wells, tailpipes
EU-HT/BC-HT Equal to API EU/BC performance Ordinary oil wells

Product Specifications:

  • Outer Diameter: Φ60.32 mm ~ Φ219.08 mm
  • Wall Thickness: 4.83 mm ~ 22.2 mm