NACE MR 0175/ISO 15156

Petroleum and natural gas industries—Materials for use in H2S-containing environments in oil and gas production

NACE MR0175/ISO 15156 gives requirements and recommendations for the selection and qualification of carbon and low-alloy steels, corrosion-resistant alloys, and other alloys for service in equipment used in oil and natural gas production and natural gas treatment plants in H2S-containing environments, whose failure could pose a risk to the health and safety of the public and personnel or to the equipment itself.

According to the definition, we can say it sour service once the enviorement contain H2S. NACE believes that there is a potential for cracking as long as it contains H2S.

What is H2s gas?

Hydrogen Sulfide (H2S) is a gas commonly found during the drilling and production of crude oil and natural gas, plus in wastewater treatment and utility facilities and sewers. The gas is produced as a result of the microbial breakdown of organic materials in the absence of oxygen. Colorless, flammable, poisonous and corrosive, H2S gas is noticeable by its rotten egg smell. With toxicity similar to carbon monoxide, which prevents cellular respiration, monitoring and early detection of H2S could mean the difference between life and death.

Impact on safety (short-term)

H2S irritates the mucous membranes of the body and the respiratory tract, among other things. Following exposure, short-term, or acute, symptoms may include a headache, nausea, convulsions, and eye and skin irritation. Injury to the central nervous system can be immediate and serious after exposure. At high concentrations, only a few breaths are needed to induce unconsciousness, coma, respiratory paralysis, seizures, even death.

Impact on health (long-term)

H2S does not accumulate in the body, but repeated/prolonged exposure to moderate levels can cause low blood pressure, headache, loss of appetite and weight loss. Prolonged exposure to low levels may cause painful skin rashes and irritated eyes. Repeated exposure over time to high levels of H2S may cause convulsions, coma, brain and heart damage, even death.

Impact on facilities

Heavier than air, H2S gas accumulates in low lying areas of poorly ventilated spaces. In oil and gas applications, sour gas (products containing H2S gas) in the presence of air and moisture may form sulfuric acid, capable of corroding metals. Facility equipment, including the internal surfaces of various components, faces reduced durability and impact strength, potentially leading to premature failure.

H2S -2
H2S

H2s in natual oil and gas production, from where?

  1. H2S produced by reduction reaction of sulfate reservoir under high temperature and high pressure formation conditions
  2. Some sulfur compounds in crude oil decompose under heat
  3. Migration and accumulation from deep crust into oil and gas reservoirs
  4. During the drilling process, some sulfur-containing drilling fluids are thermally decomposed under the conditions of the bottom layer or produced under the action of bacteria

Standard NACE MR 0175 consists of below three parts,

  1. General principles for selection of cracking-resistant material.
  2.  Cracking resistant carbon and low alloy steels, and the use of cast iron.
  3. Cracking-resistant CRAs (corrosionresistant alloys) and other alloys

Cracking and Corrosion:

HIC-hydrogen-induced cracking 

planar cracking that occurs in carbon and low alloy steels when atomic hydrogen diffuses into the steel and then combines to form molecular hydrogen at trap sites

NOTE Cracking results from the pressurization of trap sites by hydrogen. No externally applied stress is needed for the formation of hydrogen-induced cracks. Trap sites capable of causing HIC are commonly found in steels with high impurity levels that have a high density of planar inclusions and/or regions of anomalous microstructure (e.g. banding) produced by segregation of impurity and alloying elements in the steel. This form of hydrogen-induced cracking is not related to welding.

HSC-hydrogen stress cracking

cracking that results from the presence of hydrogen in a metal and tensile stress (residual and/or applied)

NOTE HSC describes cracking in metals that are not sensitive to SSC but which may be embrittled by hydrogen when galvanically coupled, as the cathode, to another metal that is corroding actively as an anode. The term galvanically induced HSC has been used for this mechanism of cracking.

SZC-soft zone cracking

form of SSC that may occur when a steel contains a local “soft zone” of low yield strength material

NOTE Under service loads, soft zones may yield and accumulate plastic strain locally, increasing the SSC susceptibility to cracking of an otherwise SSC-resistant material. Such soft zones are typically associated with welds in carbon steels.

SWC-stepwise cracking

cracking that connects hydrogen-induced cracks on adjacent planes in a steel

NOTE This term describes the crack appearance. The linking of hydrogen-induced cracks to produce stepwise cracking is dependent upon local strain between the cracks and embrittlement of the surrounding steel by dissolved hydrogen. HIC/SWC is usually associated with low-strength plate steels used in the production of pipes and vessels.

SCC-stress corrosion cracking

cracking of metal involving anodic processes of localized corrosion and tensile stress (residual and/or applied) in the
presence of water and H2S

NOTE Chlorides and/or oxidants and elevated temperature can increase the susceptibility of metals to this mechanism of attack.

SOHIC-stress-oriented hydrogen-induced cracking

staggered small cracks formed approximately perpendicular to the principal stress (residual or applied) resulting in a “ladderlike” crack array linking (sometimes small) pre-existing HIC cracks
NOTE The mode of cracking can be categorized as SSC caused by a combination of external stress and the local strain
around hydrogen-induced cracks. SOHIC is related to SSC and HIC/SWC. It has been observed in parent material of
longitudinally welded pipe and in the heat-affected zone (HAZ) of welds in pressure vessels. SOHIC is a relatively uncommon phenomenon usually associated with low-strength ferritic pipe and pressure vessel steels.

SSC-sulfide stress cracking

cracking of metal involving corrosion and tensile stress (residual and/or applied) in the presence of water and H2S

NOTE SSC is a form of hydrogen stress cracking (HSC) and involves embrittlement of the metal by atomic hydrogen that is produced by acid corrosion on the metal surface. Hydrogen uptake is promoted in the presence of sulfides. The atomic hydrogen can diffuse into the metal, reduce ductility and increase susceptibility to cracking. High strength metallic materials and hard weld zones are prone to SSC.

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If you want to get standard NACE MR 0175/ISO 15156, click below link, please.

NACE-MR0175-ISO15156-specification