Water line corrosion

Reaction of iron containing a discontinuous magnetite scale with oxygenated water, crevice corrosion, water-line attack, long-line corrosion of buried iron pipes, etc. — separable A/C type. 

White, friable corrosion products composed of Bayerite AI2O3 3H2O, caustic, and NaA102 cover corroded areas (Fig. 8.3). The white corrosion product and deposit usually test as distinctly alkaline when mixed with distilled water. Corrosion products usually cling tenaciously to the underl3dng metal and do not form voluminous lumps. Instead, corrosion products line and coat generally wasted surfaces below. 

Differences in temperature and concentration can in principle lead to corrosion cell formation, but have little effect below the water line. On the other hand, they have to be taken into account in the interior corrosion of containers and tanks in relation to their service operation (see Section 2.2.4.2). Generally the action of corrosion cells can be reduced or eliminated by cathodic protection. 

Carbon Dioxide CO2 Corrosion in water lines and particularly steam and condensate lines Aeration, deaeration, neutralization with alkalies, filming and neutralizing amines... 

Oxygen O2 Corrosion of water lines, heat exchange equipment, boilers, return lines, etc. Deaeration, sodium sulflte, corrosion inhibitors, hydrazine or suitable substitutes... 

Carbon dioxide COj Results in the corrosion of water lines, especially steam and condensate lines. 

S = Safety what are the consequences of failure If they are serious, a more resistant material than usual may be justified. For example, on a plant where leaking v. ater would react violently with process materials, the water lines were made from a grade of steel resistant to stress corrosion cracking (from the chloride in the cooling water) as well as rust. 

Fig. 1.48 Examples of differential aeration cells (a) and (b) Differential aeration cells formed by the geometry of a drop of NaCl solution on a steel surface (c) differential aeration cells formed by the geometry of a vertical steel plate partly immersed in a NaCl solution. Increasing concentrations of Na2 CO3 decrease the anodic area (d) until at a sufficient concentration attack is confined to the water line (e) (/) shows the membrane of corrosion products formed at water...

Severe attack frequently occurs at a water-line, which in practice can range from structural steel partly immersed in a natural water to a lacquered tin can used for containing emulsion paint. This can be illustrated by adding increeising amounts of sodium carbonate to a sodium chloride solution in which a steel plate is partly immersed (Fig. 1.48c, d and e). With increase in concentration of the inhibitor, attack decreases and becomes confined to the water-line. The attack at the water-line is intense and is characterised by a triangular pasty mass of corrosion products bounded on the upper surface by a dark-brown membrane that follows the contour of the water-line. The mechanism of water-line attack is not clear, but it is likely that the membrane of corrosion products results in the formation of an occluded cell, in which the anolyte and catholyte are prevented from mixing. These occluded cells are discussed in more detail subsequently. 

Recently, attention has been directed to a study of the problem of grooving corrosion in line-pipe steel welded by high frequency induction or electric resistance welding. In sea water, it seems to be related to high sulphur content in the weld zone, the type of environment, its temperature and velocity The importance of sulphur is significant since Drodten and... 

Sometimes it is possible to add corrosion inhibitors to an aqueous product that is to remain in contact with tinned steel. The normal inhibitors used for protecting steel, e.g. benzoate, nitrite, chromate, etc. are suitable, provided that they are compatible with the product and that the pH is not raised above 10. In a closed container with an air-space, such inhibitors will not protect the zone above the water-line, and possibly not the water-line zone itself, against condensate. Volatile inhibitors have been used to give protection to these areas. 

Materials may be subject to intense localised attack at the liquid level when they are partially immersed in a solution under conditions where the water line remains at a fixed position for long periods. This attack may be the result of concentration cell effects complicated by differences in the nature and adherence of corrosion-product films as they form in the water-line region as compared with those that form above or below this region. 

Power Generation Corrosion resistant linings for water treatment plant and cooling pipelines. Wear- resistant linings for coal handling plant, pulley rubber lagging for conveyor rollers etc. Soft natural rubbers and other synthetic rubbers... 

Water and Effluent Treatment in Nuclear and other chemical plants. Corrosion resistant linings for water treatment vessels and pipelines, pumps, valves, flowmeters, agitators, chemical dosing tanks, effluent tanks etc. Soft natural rubber or ebonite, EPDM, butyl, neoprene or hypalon. 

On older process units, you may still encounter piping with sentry holes. Let s say I have a Vfc-in thick pipe. The corrosion allowance for the pipe is Vi in. A number of small holes are drilled into the pipe, to a depth of in. When we start leaking at these small holes, this means that the pipe has corroded to its discard thickness in the area of the sentry hole. Incidentally, you can stop the resulting leak, at least in carbon steel water lines, with a brass wood screw and a screwdriver. I have also done this on hydrocarbon lines under an 80 psig pressure, but perhaps that is not too smart. 

Hiac 2000 liquid particle counter provides an inexpensive means to transfer up to four channels of particle size information data from sensor to host computer system. Data can be viewed in real-time via a liquid erystal display. The 2000 interfaces to all Hiac liquid sensors including the MicroCount, submicron and HRLD laser sensors. Applications include point-of-use monitoring for corrosive chemieal delivery systems, DI water lines, wet process tools, hydraulic oil systems and parts cleaning... 

In addition, the presence of alkalinity due to bicarbonate, carbonate, and hydroxide ions is often the predominant cause of foaming and carry over of solids with steam, resulting in corrosion of metal and damage to auxiliary equipment (24). Furthermore, the presence of other metal ions such as iron and manganese can discolor water and form deposits in water lines and boilers, and interfere with dying, tanning, and paper manufacture. 

Insulation. It is often necessary to connect two types of metal, for example, galvanized water Service pipes to a hot water heater from which copper hot water lines emerge. The corrosion cell that would develop in this case (Fig. 7-9) can be eliminated by inserting a dielectric coupling between the galvanized pipe and the copper pipe which effectively breaks the external circuit and eliminates the corrosion cell. However, this is not common practice because brass fixtures are used in nearly all systems instead of galvanized material. 

Installing direct current (DC) electrical-based remediation systems in urban areas also requires containment of stray voltage and current. DC systems can cause corrosion of buried gas and water lines or wreak havoc on cathodic protection systems. A good design can minimize the impacts, but sometimes, extra sacrificial anodes need to be installed to contain the electric field, adding to the cost of installation. 

A wide range of cells can be used for corrosion experiments. As mentioned, the selection of the cell is connected to the form of the sample and the masking scheme. It is often possible to simply immerse a sample into a beaker. Fig. 1. The water line can be managed with a flag electrode, or by masking the sample to expose only a submerged area. 

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