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What is the minimum partial pressure of H2S that requires compliance with NACE MR0175? from Ivan Gutierrez on Vimeo.
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Oil and Gas Corrosion Ltd is an independent materials and corrosion consultancy for the Oil and Gas industry. Oil and Gas Corrosion Ltd is under the guidance of Ivan Gutierrez. Ivan has more than 20 years’ experience in materials and corrosion and is a member of the National Association of Corrosion Engineers (NACE), a professional member of the Institute of Corrosion (MICorr) and the Society of Petroleum Engineers (SPE). He is a recognised materials and corrosion authority recognised as a Great Britain national expert member of the British Standard Institution committee PSE/17/67/7 “Corrosion Resistant Materials” and internationally as a member of Task Group 299 on the Oversight of Maintenance Panel for NACE MR0175 / ISO 15156. “Materials for use in H2S-containing environments in oil and gas production”, IOGP 15156 Committe (ISO/TC 67/WG 7 “Corrosion Resistant Materials”. Ivan is also a member of ISO/TC 67/WG 8 Materials, corrosion control, welding and jointing, and non-destructive examination (NDE) which is responsible for standards such as ISO 21457 “Materials selection and corrosion control for oil and gas production systems”. Oil & Gas Corrosion has headquarters in the United Kingdom providing services to clients across the globe.
Question 1: I am preparing a “position” document regarding SSC on behalf of my company. I am trying to understand the NACE definition for sour/non-sour (with relation to NACE MR0175). The definition of sour service is provided by NACE. That states, “exposure to oilfield environment that contain H2S and can cause cracking by the mechanisms addressed by this part . . .” However, this needs further qualification as the environmental conditions (degree of H2S and pH) may determine whether cracking can result. This is found in 7.2.1.3 of part 2 within NACE MR0175/ISO 15156, the document that refers to carbon steel (ISO 15156-2). For environments with a partial pressure of H2S below 0.3 kPa (0.05 psi) the document states, “Normally, no precautions are required for the selection of steels for use under these conditions”
Answer 1: There is no “non-sour” limit as some steels can still be susceptible below the limit of 0.05 psi (0.3 kPa).
This question is in relation to NACE MR0175/ISO 15156-2 Clause 7.2.1.3
Reference: ISO 15156 Maintenance Panel Inquiry #2009-11, Part 1
Part 2: While not explicitly stated, the implication of that statement is that an environment with a partial pressure below 0.3 kPa is regarded as “non-sour.” This is reinforced later, where Annex C, C.2 defines H2S partial pressure isobars to determine “if a system is sour.” Line 1 of Figure C.1 (0.3 kPa) identifies the demarcation between “sour” and “non-sour” conditions (referred to as being in accordance with Option 1, where environments below 0.3 kPa require no precautions), while lines 2-5 identify the degree of sourness (Option 2—prequalification of material or specific testing needs to be performed).
Answer 2: In addition for CRAs, 15156-3 has no defined “non-sour” limit. Due to the wide range of environmental cracking resistance of CRAs, particularly those not listed in 15156-3, a non-sour limit would be so low (i.e., minimum detection level) that it would be useless.
Reference: ISO 15156 Maintenance Panel Inquiry #2009-11, Part 2
