Corrosion testing 1 INDEX

Since the corrosion resistance of anodic films on aluminium is markedly dependent on the efficacy of sealing (provided the film thickness is adequate for the service conditions), tests for sealing quality are frequently employed as an index of potential resistance to corrosion. While it is admitted that an unequivocal evaluation of corrosion behaviour can only be obtained by protracted field tests in service, accelerated corrosion tests under closely controlled conditions can also provide useful information in a shorter time within the limitations of the particular test environment employed. 

Figure 7.3 A graphical representation of the highly redundant index of the Corrosion Tests and Standards handbook. 

The relative susceptibHity of several commercial aHoys is presented in Table 8. The index used is a relative rating based on integrating performance in various environments. These environments include the harsh condition of exposure to moist ammonia, Hght-to-moderate industrial atmospheres, marine atmosphere, and an accelerated test in Mattsson s solution. The latter testing is described in ASTM G30 and G37 (35,36) and is intended to simulate industrial atmospheres. The index is linear. A rating of 1000 relates to the most susceptible and zero designates immunity to stress corrosion. 

Test method for corrosivity index of plastics and fillers... 

Oilfields in the North Sea provide some of the harshest environments for polymers, coupled with a requirement for reliability. Many environmental tests have therefore been performed to demonstrate the fitness-for-purpose of the materials and the products before they are put into service. Of recent examples [33-35], a complete test rig has been set up to test 250-300 mm diameter pipes, made of steel with a polypropylene jacket for thermal insulation and corrosion protection, with a design temperature of 140 °C, internal pressures of up to 50 MPa (500 bar) and a water depth of 350 m (external pressure 3.5 MPa or 35 bar). In the test rig the oil filled pipes are maintained at 140 °C in constantly renewed sea water at a pressure of 30 bar. Tests last for 3 years and after 2 years there have been no significant changes in melt flow index or mechanical properties. A separate programme was established for the selection of materials for the internal sheath of pipelines, whose purpose is to contain the oil and protect the main steel armour windings. Environmental ageing was performed first (immersion in oil, sea water and acid) and followed by mechanical tests as well as specialised tests (rapid gas decompression, methane permeability) related to the application. Creep was measured separately. 

The ASTM D-3948 Water Separation Index, Modified (WSIM) Test is used to identify the emulsifying tendencies of additives in jet fuel. A high concentration of film-forming corrosion inhibitors has been shown to severely degrade the water separation tendencies of jet fuel. Treat rates as low as 20 ppm of some inhibitors can degrade the WSIM to a failing rating. 

In all probability, any serious prediction or evaluation of an actual recirculating cooling water, based on an index or model calculated from an analysis of the cooling water, is of dubious validity, as problems of scale and corrosion do not originate at the precise time of sampling and testing. They have already occurred. 

The test substance will not be studied for eye irritation if it is a strong acid (pH of 2.0 or less) or strong alkali (pH of 11.0 or greater) and/or if the test substance is a severe dermal irritant (with a primary dermal irritation index (PDll) of 5-8) or causes corrosion of the skin. 

Properties Volatile, colorless liquid. Fp -90.595C, bp 98.428C, refr index 1.38764 (20C), d 0.68368 (20C), flash p 25F (-3.89C) (CC). Soluble in alcohol, ether, chloroform insoluble in water distillation range 93.3-98.9C vap press 2.0 psi (a)(37.7C) (max). Color Saybolt +30 (min), maximum sulfur content 0.01 wt %, corrosive passes ASTM D 130-30 test, autoign temp 433F (222C). 

An indication of naphtha composition may also be obtained from the determination of aniline point (ASTM D-1012, IP 2), freezing point (ASTM D-852, ASTM D-1015, ASTM D-1493) (Fig. 4.2), cloud point (ASTM D-2500) (Fig. 4.3), and solidification point (ASTM D-1493). And, although refinery treatment should ensure no alkalinity and acidity (ASTM D-847, ASTM D-1093, ASTM D-1613, ASTM D-2896, IP 1) and no olefins present, the relevant tests using bromine number (ASTM D-875, ASTM D-1159, IP 130), bromine index (ASTM D-2710), and flame ionization absorption (ASTM D-1319, IP 156) are necessary to ensure low levels (at the maximum) of hydrogen sulfide (ASTM D-853) as well as the sulfur compounds in general (ASTM D-130, ASTM D-849, ASTM D-1266, ASTM D-2324, ASTM D-3120, ASTM D-4045, ASTM D-6212, IP 107, IP 154) and especially corrosive sulfur compounds such as are determined by the Doctor test method (ASTM D-4952, IP 30). 

In aqueous systems the dilemma often facing the water chemist is whether or not a particular industrial water is likely to be scale forming or corrosive. The reason for this diffiiculty may be attributed to the presence of CaCO (see Chapter 8). A simple test that may be applied to a water to provide a qualitative assessment of the problem is to add powdered CaCO to the water. If the water is supersaturated in respect of CaCO the addition of the solid particles will cause precipitation from the solution. Under these conditions there is a reduction in the pH of the water. It may be said that the water has a positive saturation index. If however the water is not saturated in respect of CaCO (such waters are corrosive), some of the added solid CaCO will enter the solution thereby increasing the hardness, alkalinity and pH. Water displaying these properties may be said to display a negative saturation index. 

Metal Alloy Corrosion electrode potential (mV, NHE) Potential following surface reduction in 10 N-HCl— reduced surface potential (mV, NHE) Rest potential in blood plasma (mV, NHE) Potential change following implantation in calf (mV, NHE) Thrombosis index (0-5) Test position d... 

F. psia Refractive index, 20/0 Color, Saybolt Acidity, distillation residue Nonvolatile matter, grams/100 ml Sulfur content, weight percent Copper corrosion Doctor test Flash point, approximate. F 0.48 0.5 0.5 1.433 ... 

The rod assemblies are usually exposed to the environment in question for 90 days, after which the wires are removed, cleaned, and reweighed. The percentage mass loss of the aluminum is the corrosion index for that time period. The data obtained can then be used to describe the severity of the atmosphere by comparing the values obtained to those empirically determined by exp>erience or by relevant testing. Environmental corrosivity is classified from negligible to very severe on this basis. Some typical atmosphere assessments made using this procedure are shown in Table 2. It has been found that a series of exposures must be made to fully characterize an environment, as the corrosion varies with the season of the year and the exposure is only for three months. 

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