Pipelines inhibitors

In the hydraulic transport of solids through steel pipelines, inhibitors of the sodium-zinc-phosphate glass type have been shown" to be effective. In the case of coal slurries the polyphosphate type was rejected because the de-oxygenating action of the coal lowered the inhibitor effectiveness. Hexavalent chromium compounds at 20 p.p.m. were more effective". ... 

Recognize corrosion problems in materials used at the site and make monitoring a normal part of the operation. Sour oil and gas operations are often conducted under high pressure and corrosive conditions. Therefore, in addition to temperature and pressure considerations, system designs for the wellhead, downhole equipment, and pipeUnes must have features to minimize the effects of corrosion and prevent an accidental release of H2S. Corrosion-inhibiting fluids can be used to prevent internal corrosion and cathodic protection can be used to prevent external corrosion. Also, during extended periods of shut-in and injection into pipelines, inhibitor applications may be beneficial. 

AH corrosion inhibitors in use as of this writing are oil-soluble surfactants (qv) which consist of a hydrophobic hydrocarbon backbone and a hydrophilic functional group. Oil-soluble surfactant-type additives were first used in 1946 by the Sinclair Oil Co. (38). Most corrosion inhibitors are carboxyhc acids (qv), amines, or amine salts (39), depending on the types of water bottoms encountered in the whole distribution system. The wrong choice of inhibitors can lead to unwanted reactions. Eor instance, use of an acidic corrosion inhibitor when the water bottoms are caustic can result in the formation of insoluble salts that can plug filters in the distribution system or in customers vehicles. Because these additives form a strongly adsorbed impervious film at the metal Hquid interface, low Hquid concentrations are usually adequate. Concentrations typically range up to 5 ppm. In many situations, pipeline companies add their own corrosion inhibitors on top of that added by refiners. 

Although there are no new methane VPO competitive processes, current technology may be usehil for the production of impure methanol in remote areas for use as a hydrate inhibitor in natural gas pipelines (119,120). 

The structures used (platforms) require monitoring in addition to sub-sea pipelines, satellite wells and other equipment (e.g. manifolds) on the sea floor. Corrosion inhibitors are widely used in internal-streams (from the reservoir and many of the downstream operations). Corrosion monitoring can provide valuable data for assessing the effectiveness of the inhibitors used and for optimising dosage rates. 

Pipelines Pipelines carrying wet gas and crude oil present a corrosion hazard and are protected accordingly by coatings and/or inhibitors. Limitations of corrosion monitoring arise from sampling, in relation to the sampling and interval, and access problems for subsea pipelines (major trunk lines). 

These same diamine materials find further application in, for example, formulations for mussel and barnacle control in large once-through, condenser cooling systems, as corrosion inhibitors and biostats for hydrostatic testing of oil and gas pipelines, and as corrosion inhibitors in food industry retort cookers. 

Amine salts of ether carboxylates inhibit internal corrosion of oil storage tanks and pipelines [230]. Furthermore it is possible to use ether carboxylates as corrosion and scale inhibitors for industrial recirculating cooling water systems, metalworking fluids, and hydraulic fluids [28,231-233]. 

The history of corrosion inhibitors and neutralizers and their invention, development, and application in the petroleum industry is documented by a review of Fisher [605]. Early corrosion inhibitor applications in each of the various segments of the industry, including oil wells, natural gas plants, refineries, and product pipelines, are reviewed. 

Corrosion inhibitors, which are used for the protection of oil pipelines, are often complex mixtures. The majority used in oil production systems are nitrogenous and have been classified into the following broad groupings ... 

The preparation of a corrosion inhibitor in the solid form allows the development of a new technique of continuous intensive anticorrosive protection for gas and oil pipelines, as well as for acidizing operations of oil wells [746]. The controlled dissolution of the solid inhibitor creates a thin protective layer on the metallic surface that prevents or minimizes the undesirable corrosion reactions. 

Accurate monitoring of inhibitor residual concentrations is most important in systems in which the volume of water is unknown or is highly variable. Frequent monitoring of the inhibitor concentration in the water exiting the pipeline is the simplest method, and sometimes the only method that can be used, to ensure that the line in fact is being protected. 

Another analytic procedure based on HPLC has been developed for the quantitative determination of nitrogen-containing corrosion inhibitors [1194]. The method was primarily developed for the analysis of certain oil pipeline condensate samples. 

Inhibitors may be classified according to their solution properties as either oil-soluble inhibitors, water-soluble inhibitors, or dispersible inhibitors. Chemical inhibitors act as film formers to protect the surface of the pipeline. Corrosion inhibitors, used for the protection of oil pipelines, are often complex mixtures. The majority of inhibitors used in oil production systems are nitrogenous and have been classified into the broad groupings given in Table 11-4. Typical corrosion inhibitors are shown in Table 11-5. For details, see also Chapter 6. 

M. A. Keimard and J. G. McNulty. Conventional pipeline-pigging technology Pt 2 Corrosion-inhibitor deposition using pigs. Pipes Pipelines Int, 37(4) 14-20, July-August 1992. 

K. C. Koshel, J. S. Bhatia, S. Kumar, and A. K. Samant. Corrosion problem in kalol injection water pipeline system and its control by using corrosion inhibitors. Ongc Bull, 25(2) 115-133, December 1988. 

The intrusive hydrogen probe (IHP-200) shown in Fig. 29 can be placed in access fittings in industrial plants (pressure vessels, pipelines) and withstands pressures up to 200 bar. It is typically used to monitor the efficiency of measures taken to diminish the risks of hydrogen damage (use of inhibitors, H2S scavengers, etc.). 

Corrosion inhibitors used to protect fuel system components such as storage tanks, pipelines, and combustion system equipment are typically dissolved in the fuel and delivered to the metal surface with the fuel. The inhibitor is deposited onto exposed metal surfaces as the fuel passes through the fuel distribution and handling system. 

The protective film formed by corrosion inhibitors can act as a lubricating film to help in reducing fluid friction within a pipeline. This property can be measured and is termed the C Factor. This friction factor is expressed as follows ... 

C Factor ratings between 155 and 160 are typical for pipelines that have been newly constructed effectively treated with a film-forming corrosion inhibitor. A low C Factor indicates that there is higher internal friction within a pipeline system, and thus a reduction in efficiency. 

For this reason, it is recommended that addition of corrosion inhibitor to previously uninhibited systems be closely monitored. Initial low level addition followed by a gradual increase in the corrosion inhibitor treat rate will help to minimize the removal of pipeline rouge and filter plugging problems. 

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