Immersion testing technique

The primaiy use of this laboratoiy technique today is as a quick check to determine the order of magnitude of a corrosion reaction. Sometimes the calculated rate from an immersion test does not look correct when compared to the visual appearance of the metal coupon. 

The NACE Landrum Wheel velocity test, originally TM0270-72, is typical of several mechanical-action immersion test methods to evaluate the effects of corrosion. Unfortunately, these laboratory simulation techniques did not consider the fluid mechanics of the environment or metal interface, and service experience very seldom supports the test... 

This encyclopedia and this chapter are focused on electrochemistry. However, a few words about nonelectrochemical techniques are in order for completeness. Exposure testing of samples to service or accelerated environments is widely used, and there are several ASTM standards describing appropriate methods. Several immersion tests for intergranular and exfoliation corrosion were mentioned in the last section. ASTM G31 describes methods for immersion testing of metals [83]. This standard practice contains mostly common sense, but also has information that will help experimentalists avoid common... 

The current RPIS inspection system has been proven on site and provides an on-line view of the inspection which can be quickly assessed. The scanning mechanisms are operated by stepper motors which may be controlled automatically or manually. They are suitable for computer control and thus can be utilised for more advanced systems. Although designed for turret heads and Immersion testing, the scanner bayonet fitting can accept other inspection heads for contact scanning or special probe assemblies for more advanced recording techniques. 

If calcnlational techniques are adopted it should be noted that established methods are usually intended to define material, properties and geometries which will result in a design capable of withstanding the required pressure loading without any impairment In the case of the 200 m water immersion test requirement for a period of not less than one hour, some degree of buckling or deformation is acceptable provided the final condition conforms with para. 657. 

In most of these studies, electrochemical methods (linear polarisation, EIS, adsorption isotherm) and immersion tests are used, but spectroscopic techniques are less common resulting in incomplete characterisation of surface modification, when compared with other substrates. 

Section HI covers Types of Tests (H. Hack, Section Editor) includirrg laboratory-accelerated tests, field tests, and service tests. The chapters in this section provide basic principles, describe test techniques and specific considerations such as specimen preparation, test duration and acceleration factors, and cite pertinent standards. Chapters included under laboratory tests are electrochemical, cabinet, immersion, high temperature, and high pressure. Field Tests chapters include atmospheric exposure, seawater, fresh water, and soil. Under service tests are industrial applications and high temperature environments. 

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. 

Immersion Test—Immersion tests involve placing coupons in deep melts. This type of test is usually used for deep melts. Some investigators have attempted to use electrochemical techniques to measure corrosion kinetics. These techniques will be discussed in the following section on deep melts. The results from immersion tests must be used... 

Nickel-base alloys respond well to most electrochemical test techniques and show active-passive behavior in many environments. Due to their rapid repassivation, however, the results obtained with potentiod3mamic techniques can sometimes be affected by scan rate and immersion time prior to starting the test [5,6], Electrochemical techniques are useful for investigating localized corrosion resistance, ASTM G 61, Test Method for Conducting Cyclic Potentio-dynamic Polarization Measurements for Localized Corrosion Susceptibility of Iron-, Nickel-, or Cobalt-Based Alloys, and general corrosion resistance, ASTM G 59, Practice for Conducting Potentiodynamic Polarization Resistance Measurements of nickel alloys. Electrochemical impedance measurement techniques have not been extensively applied to nickel alloys. 

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