Corrosion inhibitors cost effectiveness

Organic inhibitors used to protect drill pipe in weighted, as well as in low-sohds muds are effective when proper attention is given to the application method. Every effort should be made to apply the inhibitor to the drill pipe rather than to mix into the drilling fluids. This permits better control of drilling fluid properties and avoids excessive corrosion inhibitor costs. 

Inhibitors The use of various substances or inhibitors as additives to corrosive environments to decrease corrosion of metals in the environment is an important means of combating corrosion. This is generally most attractive in closed or recirculating systems in which the annual cost of inhibitor is low. However, it has also proved to be economicaUv attrac tive for many once-through systems, such as those encountered in petroleum-processing operations. Inhibitors are effective as the result of their controlling influence on the cathode- or anode-area reactions. 

Use of inhibitors. Because corrosion is such a vital aspect of the erosion-corrosion process, inhibitors that will reduce corrosion under conditions of high fluid velocity have been a cost-effective method of dealing with erosion-corrosion. For example, injection of ferrous sulfate either intermittently or continuously has been successful in inhibiting erosion-corrosion, especially with copper-base alloys. 

Because of the relatively low cost of many of the chemicals used in drilling fluids, development of more cost effective additives is a major challenge. However, improved high temperature polymers, surfactants, and corrosion inhibitors are under development in many laboratories. 

The known hazardous effects of most synthetic corrosion inhibitors are the reasons for the search of safer and environmentally friendly natural products. Plant extracts are viewed as an incredibly rich source of naturally synthesized chemical compounds that can be extracted at low costs. Naturally occurring substances such as vanillin [1], Opuntia extracts [2], lawsonia extract [3], natural honey [4] and extracts of chamomile, halfabar, black cumin and kidney bean [5] are some... 

Clay filtration can be utilized to effectively remove polar compounds such as corrosion inhibitors, electrical conductivity improvers, and antioxidants from jet fuel. Also, more costly molecular sieve techniques can be utilized to remove contaminants from jet fuel. 

Molybdate s low toxicity to fish and other aquatic life has helped to gain recognition in recent years as a corrosion inhibitor. Molybdate forms its protective film by adsorption on metal surfaces. When chloride and sulfate anions are present in the cooling water environment, they compete for adsorption, and high concentrations of molybdate are needed for effective passivation of the metal surfaces. In order to be able to reduce the molybdate concentration for cost-effective levels, synergistic blends are made up that include other inhibitors such as phosphorates and zinc. 

Aromatic azoles are specific corrosion inhibitors for copper. They also show promise for acting synergistically with other inhibitors to lower corrosion rates on mild steel. One of the more cost effective aromatic azole inhibitors is tolytriazole (TTA). It and other azoles, however, are, subject to degradation in environments containing chlorine (Roti 1985). Azoles can also be quite dangerous to human health, and must be used with care. 

It is extremely important that oxidized starch reagents are highly effective corrosion inhibitors of black metals [14] that reduces costs on carrying out of drilling operations connected with equipment deterioration. 

Passivation Inhibitors. Examples of passivators (anodic inhibitors) include chromate, nitrite, molybdate, and orthophosphate. AH are oxidizers and promote passivation by increasing the electrical potential of the iron. Chromate and nitrite do not require oxygen, and thus, can he the most effective. Chromate is an excellent aqueous corrosion inhibitor, particularly from a cost perspective. However, owing to health and environmental concerns, use of chromate has decreased significandy and will probably he outlawed soon. Nitrite is also an effective inhibitor, but in open systems it tends to be oxidized to nitrate. 

It would appear that ozone has a significant potential as an additive to combat fouling, in particular as a biocide to reduce biofouling. More detailed work is required however to improve the technology and in particular, to optimise dosing requirements to improve cost effectiveness. Investigations of the use of ozone in relation to other additives, e.g. corrosion inhibitors are also necessaiy. 

Continuous ferrous sulphate addition has been used for many years to reduce water side corrosive attack of steam condenser tubes. It is usually applied to once through cooling water systems because of its low cost, to provide an iron-rich protective film on the tube surface. For recirculation systems other more expensive, corrosion inhibitors are generally employed. Two phases of the ferrous sulphate treatment programme may be recognised. The first phase involves the initial laying down of the protective film. The second phase involves the maintenance of the film, which would be otherwise destroyed by the shear effects of flow. 

In Chapter 14 the use of additives to combat potential fouling was discussed. In the use of chemical treatment for cooling water there has to be an emphasis on effective and rapid dispersion since the concentration of the additives employed must be low, i.e. a few mg/l where possible, to minimise cost and to reduce potential pollution problems. In general the additive formulation will be based on the need to limit corrosion (i.e. the use of corrosion inhibitors), scale formation (i.e. the use of crystal modifiers, dispersants or threshold chemicals or a combination) and biofouling (i.e. the use of biocides and dispersants). In many installations additives are injected on the suction side of the main pump so that turbulence within the pump will provide rapid mixing. In very large cooling systems multiple injection nozzles will be required to enhance distribution. 

Selection of corrosion inhibitors is a complex task that depends on many factors. The cost effectiveness of the inhibitor may be obtained from the relationship ... 

Cost effectiveness = Relative effectiveness x dosage x price per weight. The inhibitor dosage rate depends on the local water conditions and temporal factors, such as the time of the year. It should be quantified in terms of percent corrosion inhibition and extension of useful life. Table 4.29 lists inhibitors used in potable water systems. 

Other methods include use of intelligent pigging as well as corrosion prediction models developed by C. De Waard and some other modifications that have been published and commercialized by several other investigators. However, after prediction and/or detection of corrosion incidents inside the pipelines, the most cost-effective method of control is the use of corrosion inhibitors. These are usually amine based and are thus water dispersible. They are usually blended with vapour phase inhibitors and probably some flow enhancers. 

The nse of corrosion inhibitors has grown to be one of the foremost methods of combating corrosion. To use them effectively, the corrosion engineer mnst, first of all, be able to identify those problans that can be solved by the use of corrosion inhibitors. Second, the economics involved mnst be considered (i.e., whether the loss due to corrosion exceeds the cost of the inhibitor and the maintenance and operation of the attendant injection systen). Third, the compatibility of inhibitors with the process being nsed must be considered to avoid adverse effects such as foaming, decreases in catalytic activity, degradation of another material, or loss of heat transfer (Klechka 2001). Finally, the inhibitor mnst be applied under conditions that produce maximum effect. 

Corrosion inhibitors are inexpensive materials that can be applied simply. However, until there is clear evidence of their envelope of effectiveness in terms of chloride level, corrosion rate, dosage cover and longevity, it will be difficult to do comparative whole life costing of inhibitor application vs. proven alternatives such as cathodic protection. 

Cost-effective corrosion- and stress corrosion/hydrogen embrittiement-resistant materiais Environmentaiiy friendiy materiais, coatings, and inhibitors Design, Mitigation Design CGC 1 Development of cost-effective, environmentally friendly corrosion-resistant materials and coatings... 

Assess the effectiveness and to optimize the costs of various corrosion inhibitors, or modified operating conditions. 

The preventive corrosion engineering technique for determination of the Corrosion Rate Break produced water level for steel, corrosion inhibitor treatment requirements, amd adloy selection cam be used to minimize the cost of corrosion protection, while at the saime time maximizing its effectiveness. 

From Fig. 4 one can now determine the effective inhibitor concentration, i.e., the concentration at which the desired steady state corrosion is obtained and since the concentration translates directly to cost. Fig. 4 also lends itself to determine the cost-effectiveness of inhibition, which is defined as the cost to achieve a certain objective. Now, one has the means to compare different products objectively on a cost-effectiveness basis. 

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