General immersion tests

General immersion tests General immersion tests can be as simple as the standard saltwater immersion test for coatings to be used in the atmosphere, or as complicated as cold wall effect immersion tests for heavy coatings to be used constantly in immersion service. It is essential to reproduce the anticipated conditions of the field exposure as dosely as possible when evaluating coatings for immersion service. 

Tests for quality of sealing of anodic coatings have become internationally standardised. They include dye spot tests with prior acid treatment of the surface (ISO 2143 1981 and BS 6161 Part 5 1982), measurement of admittance or impedance (ISO 2931 1983 and BS 6161 Part 6 1984), or measurement of weight loss after acid immersion (ISO 3210 1983 and BS 6161 Part 3 1984, and ISO 2932 1981 and BS 6161 Part 4 1981). Of these the chromic-phosphoric acid immersion test (ISO 3210) has become the generally accepted reference test. 

Chemical corrosion tests focus primarily on resistance to surface and selective corrosion. In general, the effect of material and corrosive medium variables can be understood with these methods. The variable potential, on the other hand, is more or less undefined and can experience time changes depending on the properties of the various partial reactions involved in corrosion. The fluctuation range of the potentials found in practice cannot be taken into account in the immersion test. Often, therefore, the results obtained in chemical corrosion testing using electrochemical methods must be further differentiated to take account of the variable potential. If the corrosion rate determined in chemical corrosion testing depends heavily on the potential, and has little to offer, but if there is only a little potential dependence it is more reliable. 

General Corrosion 28% Total Immersion Tests (Atmospheric Autoclave) G31... 

Pitting and crevice corrosion tendencies of a material in a select environment may be determined by immersion testing or by electrochemical techniques. Immersion testing generally involves visual examination and dimensional analysis after exposure of a test specimen to a select environment. Electrochemical methods usually involve exposure of a test specimen to a select environment and graphical interpretation of data. 

Two frequent alternatives to ASTM B 117 testing used in the evaluation of general and galvanic corrosion performance have been (1) alternate immersion testing (30 s immersion in 3 % NaCl followed by 2 min in air [4,5,7], or (2) continuous immersion in 3 or 5 % NaCl for a period of three... 

Evaluation of the protective ability of coatings generally is made in salt spray cabinets, such as those covered in ASTM B 117 and G 85 or in the 3.5 % NaCl alternate immersion test (G 44). 

The suitability of a rubber for use in contact with an oil or chemical is thus assessed hy immersing a sample in fluid and measuring the resulting increase in weight or volume. Such tests represent more severe conditions than are generally encountered in actual service, since few commercial seals are immersed for longer than 24 h and, even flien, only partial immersion is likely. In actual use, only a part of the seal s surface area is exposed to fluid attack. Tests have shown that totally immersed test specimens swell three to six times more than those exposed to fluid on one surface only. It makes sense therefore that a stock may perform well in use, even though in total immersion tests the volume swell may he 100% or more. On the other hand, flie... 

The dangers posed by acetone mean that it is not appropriate for general use in a manufacturing facility. Special training in storage, use, and disposal is required. Only personnel who have been trained are allowed to handle acetone and to perform the immersion test. 

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