Corrosion resistant alloys are mixtures of various metals such as stainless steel, chrome, nickel, iron, copper, cobalt, molybdenum, tungsten and/or titanium. Combined, these metals can resist corrosion more effectively than standard carbon steel pipe.
The advantages of corrosion resistant alloys in the short term, corrosion resistant alloys protect your well against the damage caused by sour gas. In the long term, corrosion resistant alloys help you realize life-cycle cost advantages by eliminating the need for costly workovers.
Corroded tubulars can lead to lost production and nonproductive time (NPT) on your well. Downhole tools and completion components that corrode can fail, which then require workovers. While completing a sour gas well with carbon steel components may save money up front, the cost of replacing it with a workover will be much higher in the long run. By completing your well with corrosion resistant materials the first time, you can realize life-cycle cost advantages.
Perhaps as few as one well out of a thousand causes corrosion, contain high levels of hydrogen sulfide (H2S), chlorides (Cl-) or carbon dioxide (CO2) [especially from secondary recovery methods like steam and CO2 injection]. Other reservoirs may contain very high pressure and high temperature (HPHT). These conditions corrode and weaken carbon steel tubulars.
In weight-loss (general) corrosion, the sour gas uniformly corrodes the metal surface. When carbon dioxide dissolves in liquid, it creates an acid that can cause rapid weight-loss corrosion in carbon and martensitic stainless steels, even at relatively low temperatures. The martensitic or chrome grades provide resistance to CO2 alone. Chlorides and H2S increase the corrosivity of the solution. Duplex and austenitic stainless steels have higher resistance, while nickel alloys generally show complete resistance.
In pitting and crevice corrosion, metal loss is highly localized. Stainless steels are highly susceptible to this type of corrosion, especially from chloride ions. By adding chromium and molybdenum to nickel you can resist pitting and crevice corrosion.
Environment-induced cracking occurs when a tubing string is under high stress in a sour well. To prevent cracking, you must consider the depth of the well (which requires stronger, yet more brittle metal) and the concentration of sour gas.
In some sour environments, corrosion can be controlled by using inhibitors along with carbon steel tubulars. However, inhibitors involve continuing high cost and may be unreliable, especially at higher temperatures. Also, adding corrosion allowance to the tubing wall increases string weight and reduces interior dimensions.
There are different kinds of corrosion resistant alloys. Each alloy’s precise composition enables it to resist a certain level of corrosion.CRA supplies:
- Martensitic Stainless Steel (Chromes)
- Duplex Stainless Steel
- Austenitic Alloy (Alloy 28)
- Nickel-Based Alloys 825, 925, 718, 945, G-3, 2550, 625 & 725
- Alloy C276
These alloys meet or exceed ISO 13680 and ISO 15156 NACE MR0175 and API standards. The strength of corrosion resistant alloys enables new engineering possibilities and more robust tools without compromising the integrity of the design
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