What is the minimum partial pressure of H2S that requires compliance with NACE MR0175? What is the maximum ppm of H2S allowed without NACE MR0175?
NACE MR0175 is an international standard that provides the requirements for metallic materials exposed to H2S in oil and gas production environments. In NACE MR0175, the presence of H2S is quantified as the partial pressure of H2S. The material requirements, as well as environmental limits, are based on ppH2S. In this video the lower limit of ppH2S for NACE MR0175 compliance is discussed.
ANSI/NACE MR0175/ISO 15156 indicates that in production conditions with partial pressure of H2S (ppH2S) below 0.3kPa (0.05psi) no special precautions are required for carbon and low alloy steels. However highly susceptible carbon and low alloy steels (high strength, heavily cold worked etc) can still be susceptible to H2S related damage mechanisms even at ppH2S below these limits. Furthermore, the risk of Hydrogen Induced Cracking is present even at partial pressure of H2S (ppH2S) below 0.3kPa (0.05psi).
For corrosion resistant alloys (CRAs) there is now ppH2S low limit, which means precautions need to be taken whenever the possibility of H2S is present.
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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.
NACE MR0175 / ISO 15156-2 Para 7.1.2 says “If the partial pressure of H2S in the gas is equal to or greater than 0.3kPa (0.05psi), SSC-resistant steels shall be selected using A.2” Could I please get clarification regarding the sour service H2S partial pressure cut-off value as NACE MR0175 / ISO 15156 use both imperial and metric units. The conversion of 0.05 psi is 0.345 kPa. Please clarify if the H2S pp cut-off for sour service is 0.3 kPa or 0.345 kPa (conversion from 0.05 psi).
The value was rounded off when converting from 0.05 psi. This limit is actually not a very sharp and accurate value and this is why 0,3 kPa value was taken as a practical engineering value. Note, however, that even below this H2S partial pressure, some materials can be susceptible to SSC as stated in 7.1.1. This means that in principle there is no cut-off value for sour service. It is just that below this value, only particularly sensitive steels can be susceptible to SSC. It is up to the user to make sure that the steel used is resistant below 0.05 psi (0.3 kPa).
This question is in relation to NACE MR0175/ISO 15156-2 Clause 7.1.2
Reference: ISO 15156 Maintenance Panel Inquiry #2009-18