The dangers of Hydrogen Sulphide (H2S) aka Sour Gas in oil and gas production are well known. A highly toxic, corrosive, flammable and explosive gas. H2S is colourless and although characterised by it “rotten egg” smell, at high concentrations can also be odourless.
H2S poses an extreme risk to health and safety of personnel. Exposure can result in serious short term and long terms effects, including rapid unconsciousness, coma, and even death.
Operators therefore implement very strict procedures and protocols for personnel working in areas where there is potential for exposure to the gas including provision of specialist training, installation of H2S gas detection systems throughout the site / facility and by issuing personnel gas monitors and breathing apparatus.
However, a significant challenge that operators face when dealing with H2S is trying to maintain the integrity of their production and transport systems as H2S is also highly corrosive.
H2S corrosion is a form of aqueous corrosion that can occur on all upstream steel components exposed to H2S, such as well tubing, flowlines, transport pipelines and processing equipment.
All water-wet internal surfaces are prone to H2S corrosion, either by produced water in the bottom of the line or condensed water in the top-of-line. Under-deposit corrosion may cause localised attacks on areas where solid particle settling and deposit build-up take place.
H2S corrosion can be highly aggressive and result in rapid and extensive damage. To try and mitigate the effects of H2S corrosion, specialist stainless alloys can be used to replace traditional types of steel, which when coupled with chemical inhibitors, can be particularly effective. However, these alloys are expensive as not only do they need excellent corrosion resistance properties but will also need to be resistant to other forms of associated attack such as sulphide stress corrosion cracking.
Also, the use of these specialist alloys is not always economically viable for all applications, for example in pipeline system where carbon steel is the only real choice available. For these cases, chemical inhibition is essential but often requires dose rates significantly higher than for sweet systems (C02).
Corrosion monitoring has the potential to offer real benefits as part of the overall corrosion management and mitigation strategy for assets where H2S corrosion is a significant threat.
Corrosion monitoring can provide accurate, real-time measurement of corrosion rates on all process facilities exposed to H2S protecting the considerable investment already made in specialist materials. It can be used to determine the effectiveness of corrosion inhibitor and dosing rates / regimes enabling optimisation of these chemicals and therefore potential significant cost savings.
Corrosion monitoring can also be trended against process data to provide key insight into the effects of changing process conditions on asset integrity.
Traditional monitoring technologies have some significant drawbacks which has limited their use:
Rosemount Wireless Permasense ultrasonic, wireless, wall thickness monitoring sensors are ideal for monitoring H2S corrosion– being non-intrusive, simple and cost effective to install and having sensitivity of small changes in wall thickness.
Advantages of Rosemount Wireless Permasense sensors:
For more information about continuous corrosion and erosion monitoring solutions, please contact our erosion and corrosion specialists.
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