Sour Service refers to an environment containing Hydrogen Sulfide (H2S), which is hazardous to human health and could significantly impact steel drilling tubulars performance.
Hydrogen sulfide is a colorless gas with the characteristic foul odor of rotten eggs; it is heavier than air, very poisonous, corrosive, flammable, and explosive.
It is hazardous. Hydrogen sulfide gas causes a wide range of health effects. Workers are primarily exposed to hydrogen sulfide by breathing it. The effects depend on how much hydrogen sulfide you breathe and for how long. Exposure to very high concentrations can quickly lead to death.
Crude oils containing an abnormally large amount of sulphur and sulphur compounds which break downÂ upon refining to liberate troublesome quantities of corrosive sulphur compounds.
Gas which contains objectionable amounts of contaminants, e.g. hydrogen sulphide and other corrosiveÂ sulphur compounds. Sour gas is natural gas or any other gas containing significant amounts of hydrogenÂ sulfide (H2S). Natural gas is usually considered sour if there are more than 5.7 milligram of H2S per cubic meter of natural gas, which is equivalent to approximately 4 ppm by volume under standard temperatureÂ and pressure.
Water which contains objectionable amounts of dissolved contaminants, e.g. hydrogen sulphide, ammonia,Â phenols etc. For sour water, the dissolved hydrogen sulfide concentration is at least 50 ppmw.
Dangers of Hydrogen Sulfide (H2S)
The detrimental effects as a result of sour service can range from small pinhole leaks to catastrophic failureÂ in pipelines owing to a number of phenomena as a result of the sour gas environment, namely: stressÂ corrosion cracking, sulphide stress corrosion cracking, hydrogen-induced cracking, hydrogen embrittlementÂ and exfoliation, and sulphide-oriented hydrogen-induced cracking.
The product can not only causeÂ deterioration to pipelines, but is potentially harmful to the environment and personnel health.Â H2S in combination with water and low pH will release free hydrogen, which can be absorbed through theÂ steel’s surface. At this point, hydrogen particles diffuse further into the steel matrix and interact with theÂ steel itself, which becomes brittle. The physical phenomenon associated with Sour Service environmentsÂ and affecting steel based products under applied or residual stress is known as H2S embrittlement or moreÂ specifically as Sulfide Stress Cracking (SSC).
Minimizing the Risk
Proper selection of materials
- Consideration of the design and operating conditions will help in the material selection process.
- Equipment and piping in wet sour service typically uses carbon steel as the primary material of construction.
- Copper and copper-based alloys such as 90/10 Cu/Ni (UNS C70600) are not recommended for wet sour services because of their susceptibility to rapid metal loss.
- The fabrication requirements and hardness limitations of NACE MR0175 should be mandatory.
Amine gas treating
Gas sweetening is the process by which petroleum products are improved by removingÂ theÂ sulphurâ€‘containingÂ Â and unsaturated compounds from natural gas and liquid hydrocarbon streams throughÂ absorption and chemical reaction.
It is also known as amine scrubbing, gas sweetening and acid gas removal, refers to a group of processesÂ that use aqueous solutions of various alkylamines (commonly referred to simply as amines) to removeÂ hydrogen sulfide (H2S) and carbon dioxide (CO2) from gases.
Hydrocarbon gas free from sulphur compounds are also called sweet gas.
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