Water corrosion testing

Overall, the two ASTM Standard Guides (G 04 and G 78) provide valuable information applicable to the design and interpretation of these natural water corrosion tests. 

The salt-water corrosion test is used to evaluate submarine splice closures. For this test a spUce closure tuid its outer housing are immersed in aerated 3.5 % sodium chloride solution for 180 days. The test is described in TA-TSY-041 [17]. The same closures are also exposed to a similar test using artificial fresh water (ASTM D 2570, Method for Simulated Service Corrosion Testing of Engine Coolants). 

ILLIUM PD passes the ASTM B117 salt spray test. Sea water corrosion tests conducted for the U. S. Navy at Portsmouth resulted in no evidence of corrosive attack on specimens stressed at 55,000 to 75,000 psi for a period of six months. 

Specifications for gas turbine fuels prescribe test limits that must be met by the refiner who manufactures fuel however, it is customary for fuel users to define quality control limits for fuel at the point of delivery or of custody transfer. These limits must be met by third parties who distribute and handle fuels on or near the airport. Tests on receipt at airport depots include appearance, distfllation, flash point (or vapor pressure), density, freezing point, smoke point, corrosion, existing gum, water reaction, and water separation. Tests on delivery to the aircraft include appearance, particulates, membrane color, free water, and electrical conductivity. 

Attack on metals can be a function of fuel components as well as of water and oxygen. Organic acids react with cadmium plating and 2inc coatings. Traces of H2S and free sulfur react with silver used in older piston pumps and with copper used in bearings and brass fittings. Specification limits by copper and silver strip corrosion tests are requited for fuels to forestall these reactions. 

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. 

Remember that the galvanic series was constructed from laboratory data using sea water as the exposure fluid. When there is a question about galvanic corrosion tendencies in actual industrial environments involving fluids substantially different from sea water, appropriate testing of candidate metals in these fluids may be warranted. 

Wilde, B. E., A Critical Appraisal of Some Popular Laboratory Electrochemical Tests for Predicting the Localised Corrosion Resistance of Stainless Alloys in Sea-water , Corrosion, 28, 283 (1972)... 

Fig. 3.50 Corrosion rate versus temperature in de-aerated sea-water continuous test exposure...

Table 3.49 Sea-water corrosion/erosion test carried out at 8 m/s at 28° C for 60 d...

To check the efficacy of grease removal, the alkali solution is rinsed away or neutralised by dipping in dilute acid. If, after removal from the acid, the draining metal surface remains wetted evenly all over for 30-60 s (or until it dries by evaporation), hydrophobic soils have been removed. Traces of grease cause the surface to de-wet, and surface tension draws the water into separate droplets. This is the water-break test. Traces of grease which remain when the work is plated do not prevent electrodeposition, but are detrimental to adhesion and corrosion resistance. 

The most widely used accelerated tests are based on salt spray, and are covered by several Government Specifications. BS 1391 1952 (recently withdrawn) gives details of a hand-atomiser salt-spray test which employs synthetic sea-water and also of a sulphur-dioxide corrosion test. A continuous salt-spray test is described in ASTM B 117-61 and BS AU 148 Part 2(1969). Phosphate coatings are occasionally tested by continuous salt spray without a sealing oil film and are expected to withstand one or two hours spray without showing signs of rust the value of such a test in cases where sealing is normally undertaken is extremely doubtful. 

Packaging materials Materials to be used in contact with metals should be as free as possible from corrosive salts or acid. BS 1133, Section 7 1967 gives limits for non-corrosive papers as follows chloride, 0-05% (as sodium chloride) sulphate, 0-25% (as sodium sulphate) and pH of water extract 5 -5-8 0. Where there is doubt, contact corrosion tests may be necessary in conditions simulating those in the package. 

The significance of the corrosion potential in relation to the equilibrium potentials and kinetics of anodic and cathodic reactions has been considered in Section 1.4, but it is appropriate here to give some examples of its use in corrosion testing. Pourbaix has provided a survey of potential measurements in relation to the thermodynamics and kinetics of corrosion, and an example of how they can be used to assess the pitting propensity of copper in Brussels water is given in Section 1.6. 

Because sodium, which is liquid between about 100°C and 881°C, has excellent properties as a heat-transfer medium, with a viscosity comparable with that of water and superior heat conductivity , much attention has been paid to liquid sodium corrosion testing of metal and alloys. Indeed, ASTM have issued a Standard Practice which can be used for determination... 

The corrosion testing of metals in natural waters is most usually conducted in field or service tests since the conditions of flow are important and often rate-determining. Testing will be concerned with mains water (potable water), river-water and sea-water or combinations of these as in estaurine conditions. Test specimens of various geometries will be used, e.g. in the... 

Test method for iron chip corrosion test for water soluble metalworking fluids Test method for accelerated weathering test conditions and procedures for bituminous materials (xenon-arc method)... 

Test method for sandwich corrosion test Recommended practice for preparing, cleaning, and evaluating corrosion test specimens Practice for aqueous corrosion testing of samples of zirconium and zirconium alloys Test method for corrosion testing of products of zirconium, hafnium and their alloys in water at 633 K or in steam at 673 K [metric] Recommended practice for conventions applicable to electrochemical measurements in corrosion testing... 

General rules for corrosion tests applicable to storage conditions Filiform corrosion test on steel Liquefied petroleum gases-corrosiveness to copper. Copper strip test Road vehicles-brake linings-resistance to water, saline solution, oil and brake fluid-test procedure... 

Visual standard for surfaces of new steel airblast cleaned with sand abrasive Autoclave corrosion testing of metals in high temperature water... 

Sharma et al. [153] have devised a gentle accelerated corrosion test using a kinetic rate equation to establish appropriate acceleration factors due to relative humidity and thermal effects. Using an estimate for the thermal activation energy of 0.6 eV and determining the amount of adsorbed water by a BET analysis on Au, Cu and Ni, they obtain an acceleration factor of 154 at 65°C/80% RH with respect to 25 °C/35-40% RH. 

Kubo, S. et al., Corrosion test on structural materials for iodine-sulfur thermochemical water splitting cycle, in Proc. 2nd Topical Conf. on Fuel Cell Tech., AIChE 2003 Spring National Meeting, New Orleans, March 30-April 3, 2003. 

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