Stainless steels inhibitor selection

Corrosive water must be avoided. If the column is made of stainless steel, the water should be low in chlorides (131). The author is familiar with one plant where steam-water operations were discontinued in stainless steel columns after it was found that chlorides in the water caused metal deterioration. Ideally, the water should contain a corrosion inhibitor. The corrosion inhibitor should be carefully selected, because several commercial inhibitors promote foaming in subsequent operation. 

On the basis of the risk factors and economics coated carbon steel with a supplemental corrosion inhibitor was preferred over the duplex stainless steel in spite of higher risk of the coated steel. The material selected for flow lines and trunk lines is shown in Table 4.43. 

Performance of Stainless Steel Rebar in Concrete Corrosion protection of steel rebar can be achieved by (i) selection of corrosion-resistant steel (ii) use of coatings (iii) addition of corrosion inhibitors such as calcium nitrite to concrete mix (iv) addition of concrete sealers (iv) use of membranes (v) use of thicker concrete overlay (vi) cathodic protection. 

Use of CRA is competitive with inhibition in deep, high-pressure wells, particularly in those locations where inhibitor supply may be a space and logistic problem. CRA includes stainless steels (austenitic, ferritic, martensitic, and duplex), nickel-based alloys, cobalt-based alloys, and titanium alloys. Economics is a major factor in alloy selection. The 13 Cr tubing has often been used in gas wells for low H2S wells. Tubing materials selection for a deep well could involve price increments between alloys of 1 to 3 million. High-strength CRA is used to minimize costs. SMYS values of 150 ksi (1000 MPa) are common. The CRA is often cold-worked to achieve the required yield strength. 

If the pipelines are located in deep water or inaccessible places, maintenance and/or replacement of pipes and clean-up of oil spills is difficult and expensive. The use of expensive stainless steel or other alloys is not a viable solution due to the required capital costs, which are not economically feasible in many cases. Hence the strategy to combat corrosion problems is to use carbon steel pipes, but reduce and, if possible, prevent the rate of material losses. An important method of corrosion reduction practiced in the oil and gas industry is the use of corrosion inhibitors. The inhibitors act by bonding to the metal surface and forming a protective film. The performance of the inhibitor depends on the metal surface, the inhibitor composition, and fluid flow conditions. Some of the inhibitors are not effective because of the multiphase flow conditions in the pipelines. When selecting an inhibitor, it is essential to know its effectiveness in the specific service environment. Detailed knowledge of the metal surface conditions, the operating temperature and pressure, the fluid properties, the solution pH, and the multiphase flow conditions is essential. 

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