Corrosion protection program

Nodal points of the platform require special attention for corrosion protection. Therefore the anodes have to be installed in the vicinity of these points, as indicated in Fig. 16-4. The spacing must be sufficiently large that the welded Joints of the nodes do not lie in the area of the lap Joints. The effort for calculating the optimal distribution with the lowest weight of anodes is considerable and has led to computer programs by which the anode distribution can be estimated [11]. 

Because of their surfactant and filming properties fatty amines such as coco-alkylamine acetate (and more especially diamines, such as tallow propylenediamine) are also occasionally employed in other types of water treatment programs. For example, they may be used as corrosion inhibitors for steel cooling systems, especially those smaller units where minimal operational control is provided. The amines must be continuously dosed to ensure good film formation (and thus corrosion protection), typically at 5 to 10 ppm active amine. They also tend to have good biostatic control properties, which provide a benefit of algal and bacterial control at no extra cost. 

A further longer term wet lay-up alternative is through the use of volatile corrosion inhibitors (VCIs) such as dicyclohexylamine acetate. These are dissolved in the water at a temperature below 60 °C, and the water is circulated for 4 to 5 hours. The boiler does not need to be completely filled because the VCI migrates to all parts of the boiler and reaches equilibrium in each of the void spaces. With traditional lay-up chemicals, the oxygen scavenger may become depleted easily (which is why the reserve usually is so high) and corrosion protection is quickly lost however, with VCI programs, there is always a volatile buffer available that maintains equilibrium and hence corrosion protection. 

Claims are sometimes made that the use of cathodic protection devices eliminates the need for any type of water treatment chemical, including oxygen scavengers (on the basis that oxygen in the FW increases the rate of zinc anode corrosion, producing both zinc ions and hydroxide ions and resulting in the removal of 02 from the BW electrolyte). Such claims that corrosion protection devices provide a complete program are spurious. 

Corrosion control of metal surfaces depends on the formation and maintenance of a protective corrosion inhibitor film on the exposed metal surface. This protective film may be established during normal application of a corrosion inhibitor program however, there will be some lag time before the film is completely built up. Metal surfaces that are exposed to the cooling water before the film is completed may become candidates for accelerated corrosion during the initial system operation. Normally, localized corrosion or pitting is common during these early stages of operation. 

In low pH cooling waters (pH 6.0 to 7.4), when treating with zinc programs, levels of 3 to 5 ppm of soluble zinc can often be obtained, which tends to provide good corrosion protection to carbon steel. Its solubility rapidly decreases as the pH rises it may only be 0.2 to 0.3 ppm or less in high pH cooling water (say pH 8.3 and above), giving rise to the risk of zinc precipitation in the bulk water. This is partly overcome by the incorporation of zinc stabilizers ( zinc dispersants or zinc enhancers ) in the formulation. 

The chemical treatment employed is a combination/derivation of an Alkaline Zinc Polymer Program and a Stabilized Phosphate Program. It operates at an alkaline pH and uses zinc to synergize with phosphate to enhance corrosion protection and reduce the amount of PO4 required (this is Chemical 1). It requires a PO4 stabilizer polymer (Chemical 2). 

W.K, Lu, R.L. Elsenbaumcr and B, Wessling, Corrosion Protection of Mild Steel hy Coatirtgs ContairUng Polyaniline, Materials Science and Engineering Program, The University of Texas at Arlington,... 

Protection of cooling system metals involves complex interrelated problems of scale and deposit prevention, control of microbiological growths and other fouling sources, in addition to corrosion mitigation by inhibitors. Corrosion control programs may be expected to vary considerably between systems, since each installation presents different environmental factors and operating problems which affect response. 

The proper corrosion maintenance program should prevent or eliminate the conditions favoring corrosion (i) trapped moisture (ii) wet insulation blankets (iii) plugged drain holes and passages (iv) chipped or missing paint (v) loss of protective finish (vi) corrosive cargo. 

The demonstrated reliability of these pipelines has required the use of several different corrosion protection schemes. To reduce attacks on the outer surfaces of pipelines, improved cathodic protection systems and coating materials (fusion-bonded epoxy, which replaced coal tar systems) have been used along with better inspection programs. 

Many engineers rely on their desalter and corrosion-inhibitor chemical vendor to formulate a corrosion protection plan for their unit. This is usually a good idea. However, one needs to know enough about this aspect of the unit to determine if the vendor representative is competent. One useful method is to ask competing chemical vendors to come up with alternative programs. 

Field tests on drinking water -Subsection water. Investigation into the corrosion behaviour of metallic materials towards drinking water. Results from the research and development program Corrosion and corrosion protection )... 

Remember that a corrosion inhibitor program is basically a coating treatment. The amount of inhibitor required depends upon the amount of metal to be protected, not upon the volume of fluid produced by the well. The amount of fluid produced determines the frequency of treatment, although it is probable that no well should go longer than three months between corrosion treatments. 

Inhibitor residuals are occasionally used to monitor corrosion control programs. By knowing at what concentration certain water soluble inhibitors give protection, we can generally tell if protection is being accomphshed. 

The primary disadvantages of chemical cleaning are the possibility of excessive equipment corrosion and solvent disposal. Chemical cleaning solvents must be assessed in a corrosion test program before their field acceptance. Chemical cleaning is performed by a contractor who specializes in this work. Some cleaning procedures are protected by patents. 

Successful corrosion control programs depend both on proper application techniques of the protective chemicals and good monitoring. Consistent record keeping by both the supplier and the customer is an essential part of a successful monitoring program. 

Surface treatment methods are currently used to prevent corrosion and enhance adhesion between metals and coating materials. For these purposes, chromate-, zinc- and phosphate-based materials are employed to increase the corrosion resistance of surfaces as well as enhance coating quality. However, some of these materials are unacceptable from an ecological and human health point of view, and an alternative system must be considered to reduce these concerns. Recently, several research programs have focused on low-toxicity materials that could replace currently used materials. These new surface treatments should improve corrosion protection and also provide good adhesion between metal and paint surfaces. ... 

Unprotected steel corrodes at a rate which is generally assumed to be 0.1 to 0.2mm per annum. Factors that influence the actual rate of corrosion include the maintenance program applied by the owner - particularly preservation of protective coatings, efficiency of cathodic protection systems in ballast tanks, corrosive properties of the cargo carried and environmental factors such as temperature and humidity. Under extreme conditions it has been known for the annual rate of corrosion on unprotected steel exposed on both surfaces to approach 1mm. 

In addition to the careful selection of structural metals, the cathodic protection of water-wetted parts may also be specified. For most boiler plant systems, however, because of the tortuous and extended waterside surfaces involved, the use of cathodic protection is only a partial solution to controlling corrosion and should never be the sole secondary protocol. Rather, cathodic protection functions well when employed as part of a more comprehensive program that includes appropriate internal chemical treatments. 

Nitrite-based programs require a relatively high application rate to ensure that all anodic areas within the system are fully protected from the risk of pitting corrosion. Undertreatment exposes anodic areas, which are subject to localized pitting as a result of the concentrating power from surrounding cathodic sites. 

Although azoles are commonly thought of as only yellow metal inhibitors, they are, in fact, used for corrosion inhibition in a wider range of metals such as steel and aluminum. They also are often incorporated in molybdate-based programs to both provide some synergism and reduce the level of molybdate required. Azoles also are employed in many types of organic-based formulations, where they improve the overall protection of steel and reduce the risk of corrosion of yellow metals due to the corrosive action of some common phosphonates. 

Insurance inspections and cleaning programs further add to the frequency at which a boiler may be out of service. During these outages and offline periods, the boiler metal waterside surfaces are especially susceptible to rapid corrosive attack and damage. Consequently, various protection protocols are employed to stave off this risk. The primary factors responsible for downtime corrosion are ... 

Where AVT programs are employed, maximum protection against boiler waterside corrosion occurs when the FW conductivity is below 3 jxS/cm. 

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