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Sour Testing

TWI provides full scale testing of pipes, girth welds, connectors and other components in aggressive environments associated with sour service.

Sour service environments, frequently encountered by the oil and gas industry, are those where there is enough hydrogen sulphide (H2S) to be corrosive and potentially cause cracking in metallic materials, leading to equipment failure.

Because of the toxic, flammable and corrosive nature of sour environments, any equipment used for these conditions needs to be made from high-strength, sour service-resistant materials that can withstand the effects of sulphide stress cracking (SSC) and other related cracking mechanisms.

Environments that are not ‘sour,’ and so do not contain significant quantities of H2S, are known as ‘sweet’ and do not pose the same risks to materials in service.

Challenges of Sour Service

Sour service conditions are characterised by the presence of significant quantities of H2S gas, which can cause various types of damage to metallic materials. These include:

  • Sulphide Stress Cracking (SSC): Causing brittle failure in carbon and low-alloy steels under stress
  • Hydrogen-Induced Cracking (HIC): Cracking that occurs within the base metal due to hydrogen absorption
  • Stress-Oriented Hydrogen-Induced Cracking (SOHIC): A form of cracking caused by hydrogen exposure
  • General or Localised Corrosion: Metal loss that can weaken equipment over time

Risks, Safety and Materials Selection

H2S is dangerous, even at low concentrations, which poses significant risks to human health and safety. In addition to this, equipment failure in sour service can potentially lead to financial, operational and environmental consequences. Because of the risks, it is important to use specialised, resistant materials to ensure equipment reliability and integrity in sour service.

The requirements for equipment and materials used in sour service conditions have been set down by organisations like NACE (now known as AMMP) and international bodies who have established standards like NACE MR0175/ISO 15156.

Sour Testing at TWI

As part of our fracture mechanics and corrosion testing services at TWI, we offer bespoke and standard test methods for parts in sour environments. We can test for a range of failure mechanisms such as ring testing for stress corrosion cracking to suit the requirements of our Members.

As part of our sour testing solutions, specialists at TWI designed and commissioned a high-pressure flow loop that enables a large range of tests to be carried out in an environment representative of field conditions.

This unique facility allows the circulation of ISO 23936-1:2009 sour fluids containing heptane, cyclohexane, toluene, carbon dioxide, hydrogen sulphide, methane and water at pressures up to 89barg and temperatures up to 130°C. An important feature of the test rig is the ability to conduct experiments under realistic field conditions in terms of flow and mass transport.

During the operation of the rig, the fluid is conditioned in the bypass loop. This fluid mixture can then be pumped through a pipe section or other component under test and the temperature, pressure and flow rate monitored remotely.

TWI’s Members have the opportunity to use this facility for applications such as conditioning of sections of fibre-reinforced composites, sealing assemblies and exposure testing of electronic components.

TWI’s established facilities for permeation monitoring of gas and liquid phases, along with rapid gas decompression and fluid sampling facilities, can be used to enhance these experiments.

Our facilities also include a fatigue test machine, built and manufactured in-house by TWI, for the full-scale sour testing of pipes, girth welds and connectors in the presence of an aggressive environment.

Capable of rotating bending and in-plane bending, the full-scale sour testing rig was the only one of its kind in the world when it was built. The rig recreates the environmental conditions of service at sea, including exposure to fluids containing H2S. It uses a servo-hydraulic control of applied load, giving precise and consistent cyclic stress ranges and includes an axial preload facility for the application of static tensile mean stress. The rig is also capable of applying variable amplitude loading spectra. You can find out more about the specifications and potential applications of this rig, below.

Full-Scale Sour Testing Rig

Potential Applications:

  1. Determination of the fatigue strength of offshore pipeline girth welds
  2. Fatigue testing of pipeline connectors
  3. An alternative to resonance testing where high frequency and mechanical interfaces make this method unsuitable
  4. Fatigue testing within sour environment
  5. Testing parts exposed to corrosive gas and fluids , including those found in power plant eg. biomass and geothermal wells

Technical Specification:

  1. Accommodates pipe sizes up to 324mm outer diameter
  2. Bending moment range up to +/-250kNm
  3. Axial preload up to 200kN
  4. Test frequency up to 2Hz
  5. Test temperature range 5–60°C

For more information please email:


contactus@twi.co.uk