Sour Service

Sour Service Experts

Charles Thompson provides expert knowledge for sour service applications for the petrochemical and oil & gas sectors with fabrication procedures that protects pipework, vessels and equipment from the effects of hydrogen sulphide (H2S) according to regulatory specifications.

Sour service and the reduction of sulphide stress corrosion is one of our particular areas of expertise. We choose materials carefully, ensuring they are fit for purpose; fabricate and weld equipment and components according to the highest benchmarks of sour service practice; and subject equipment and components to thorough testing.

Please see below for further details of our materials, fabrication procedures, welding options and other policies, or contact us to discuss your requirements.

Sour Service Materials and Procedures

When choosing materials for sour service, our engineers make a full project assessment, including design life, cost, inspection and maintenance, safety and environmental challenges, failure risk evaluations and other specific criteria.  

We seek to minimise corrosion, failure (and risk to health, environment and material assets), and provide equipment and components with exceptional strength that is resistance to brittle fracture.

Alloy 625 (UNS No. N06625)

  • Nickel-Chromium Alloy containing molybdenum and niobium
  • Available in annealed and solution annealed forms
  • Excellent combination of strength and corrosion resistance
  • High tensile strength at elevated temperatures when compared to carbon and Stainless Steels
  • Service temperatures from cryogenic to 1800F/982.23C
  • Excellent ductility and toughness at low temperatures
  • Outstanding creep, rupture and fatigue strength
  • Outstanding corrosion resistance to stress corrosion cracking, pitting, and crevice corrosion
  • Resistance to high temperature oxidation and carburisation
  • Absence of embrittling intermetallic phases such as sigma when exposed for long periods at high temperatures
  • Nickel group listed in NACE MR 0175 for sour service
  • ASME approval for pressure vessel application

Alloy 825 (UNS No. N08825)

  • Nickel-Iron-Chromium alloy containing molybdenum, copper and titanium
  • Excellent combination of strength and corrosion resistance
  • Service temperatures from cryogenic to 1000F/538C
  • Not normally used where creep-rupture properties are design factors
  • Excellent ductility and toughness at low temperatures
  • Designed to provide exceptional corrosion resistance in many corrosive environments
  • Outstanding corrosion resistance to stress corrosion cracking, pitting, and crevice corrosion
  • Good intergranular corrosion resistance
  • Nickel group listed in NACE MR 0175 for sour service
  • ASME approval for pressure vessel application

Alloy 625/825 Welding and Testing for Sour Service

CTL uses GTAW (TIG) and SMAW (MMA) processes to achieve satisfactory results for:

  • Radiography
  • Macroscopic examination (x5)
  • Hardness survey
  • Toughness (Charpy impact tests)
  • Corrosion (G28 method A) testing

Weld preparations are primed by machining or grinding, followed by cleaning.  The storage and pre-treatment of consumables is in accordance with the CTL client-approved procedure.

Duplex Stainless Steel

  • An Austenitic-Ferritic (two-phase) alloy with high levels of Chromium, Nitrogen and often Molybdenum
  • Very good resistance to localised and uniform corrosion, including Chloride stress corrosion cracking resistance and pitting corrosion resistance
  • Higher strength than standard Stainless Steels
  • Higher corrosion resistance than type 316 Stainless Steel in corrosive chemicals including Sulphuric, Phosphoric and Nitric acids
  • Good resistance to pitting and crevice corrosion in seawater
  • High stress corrosion resistance
  • Lower thermal expansion than Austenitic Stainless Steels
  • Higher thermal conductivity than Austenitic Stainless Steels
  • Listed in NACE MR 0175 for sour service
  • ASME Approval for pressure vessel application

Super Duplex Stainless Steel

  • Enhanced properties provided by Chromium, Nitrogen and Molybdenum
  • Demonstrates good resistance to stress corrosion cracking in the presence of Hydrogen Sulphide and Chlorides at low temperatures
  • Exhibits a very good resistance to intercrystalline corrosion
  • Excellent corrosion resistance in a wide variety of challenging environments
  • Outstanding resistance to pitting and crevice corrosion in seawater and other Chloride-containing environments, with critical pitting temperature exceeding 50C
  • High strength compared to austenitic and 22%Cr Duplex Stainless Steels
  • Excellent ductility and impact strength at both ambient and sub-zero temperatures
  • High resistance to abrasion, erosion and cavitation erosion
  • Excellent resistance to stress corrosion cracking in chloride containing environments
  • Caution should be observed regarding conditions of high partial pressure of Hydrogen Sulphide and where the materials are subject to high stress
  • Listed in NACE MR 0175 for sour service
  • ASME approval for pressure vessel application

Duplex/Super Duplex Welding and Testing for Sour Service

CTL uses GTAW (TIG) and SMAW (MMA) processes to achieve satisfactory NDT results for:

  • Hardness
  • Toughness (Charpy impact tests)
  • Ferrite/microstructure
  • Corrosion (G48A) testing

Duplex Material Purchasing Strategy Example

Pipe to ASTM A790 UNS S31803

  • Solution treated and water quenched, pickled finish
  • Heat Treatment Charts are required in final certification
  • Correct Heat Treatment is critical to this material
  • Type 3.2 material certification
  • NACE MR0175 / ISO 15156 certified.
  • Hydro test and non-destructive electric test (Eddy Current)
  • Ultrasonic examination to ASME V
  • Corrosion testing to ASTM G48 Method A
  • Hardness testing to ASTM A370 (28 HRC max)
  • Impact testing to ASTM A370 (1/4t <30mm, 1/2t >30mm) 50J at -46ºC
  • Microscopic examination to ASTM E562 and A923
  • 35-65% Ferrite in austenite.
  • Intermetallic phases and precipitates shall be assessed (<1% in any 1mm2) and no preferential grain boundary attack
  • Ferritescope testing

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For more information about how we can help you, call our team on
+44 (0)1709 584 011 or alternatively, fill in our short contact form and we will get back to you within 24 hours.