In-service testing

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. 

The Marine Corrosion Working Party of the European Federation of Corrosion has published valuable advice on corrosion testing in service... 

Warner A. Cost-effective toxicology testing, In-Service Training and Continuing Education, American Association for Clinical Chemistry 1996 17(2) February. 

Regenerative biofilms have been tested under industrial conditions in the chill water system at the University of California, Irvine (UCI) and at Three Mile Island Nuclear Power Station (TMI) using EIS [123, 124]. Reciprocal polarization resistance (l//fp), considered to be directly proportional to the corrosion rate, was compared as a function of time for preexposed mild steel samples tested in unaltered (standard) service water and samples tested in service water inoculated with protective bacteria. Substantial differences in... 

Examination Techniques and Procedures Inspection Intervals Examination Records System Leakage and Pressure Tests In-Service Testing of Valves Acoustic and Flow-Induced Vibrations... 

As part of the USNRC s risk-informed regulatory initiative, low power and shutdown conditions should be considered by a utility when making a risk-informed regulatory submittal request for a change to graded quality assurance, in-service-testing, in-service-inspection, or technical specifications. 

Analysis and mechanical tests in-service surveU-lance for irradiation effects fracture toughness tests (12.5 mm compact tension specimens or thicker) for quahty control of components and qualification of welding procedures low temperature irradiation effects on external vessel supports. 

When it is impractical to test in service, laboratory simulations of the corrosive exposures may be necessary. Immersion tests, cabinet tests, and electrochemical measurements are in widespread use, but do not necessarily provide results that correlate with service exposures. However, relative rankings of selected materials under controlled testing conditions can be useful in materials development. 

Deviations from current requirements for manu cturing, testing, in-service inspection, and maintenance can lead to safety equipment not performing its intended safety functions. 

The acronym "CIAPES" stands for - Controle et Inspection des Appareils a pression lors de I Epreuve et en Service (Control and Inspection of Pressure Vessels during Testing and in Service). 

Parallel to tliese tests, CETIM has informed the administration which establish regulations for pressure vessels of the advantage of the acoustic emission method for the inspection in-service. 

Some partners of the programme have already obtained the authorization to make in-service pneumatic test monitored by acoustic emission instead of hydraulic tests. 

Both testing systems are safe in service and can be used for special control by safety... 

The modern Russian MIA flaw detectors use pulse version of the method [1-3], which peirnits to produce very portable (0.7 - 1.5 kg) and simple instruments, convenient especially for in-service testing. The objects to be tested are multilayer structures of reinforced plastics, metals and other materials honeycomb panels, antenna fairings, propellers, helicopter rotors and so on. In mentioned instruments amplitude-frequency analog signal processing is used. 

NDT equipment imported in lots in the process of state testing are examined both on their conformity to the requirements of safety standards (ISO, CEN, lEC) and standards of the manufacturer and its availability for calibrartion in service. 

For pipelines in service in chemical plants, it is not usually convenient to place a radiation source inside the pipe and position it to irradiate each welded joint. The radioisotope source container maybe placed on the outer surface of the pipe. The radiation beams then pass through two pipe wall thicknesses to expose films placed diametrically opposite the radiation source, also on the outside of the pipe wall. Other methods, such as magnetic particle inspection of welds in steel pipe, or ultrasonic inspection of welds in pipes of all materials, supplement x-rays in many critical appHcations. The ultrasonic tests can often detect the thin, laminar discontinuities parallel to the pipe surface or the incomplete fusion discontinuities along the weld... 

Eor steel and other ferromagnetic materials, property deterrnination is more difficult. Other tests are made to measure the continuity of protective metallic coatings. Residual stresses induced in welded stmctures and in components in service owing to chemical attack may contribute to early failure. 

Since oxygen uptake is tested in a closed system, loss of volatilization is minimal. This type of test is not reUable for estimating service life under conditions in which the polymer is exposed to air movement. 

The reproducibility of test results between labs using the neutral salt spray tests has not been consistent, but the repeatability, within one lab, is better, and the test has value in comparing variations in coating systems. Correlation of hours of exposure in the salt spray test to actual performance of the plated part in service, even in marine atmospheres, is not consistent and usually avoided. A classic example is that cadmium deposits outlast zinc deposits on steel in salt spray tests and clean marine atmospheres, yet zinc outlasts cadmium when exposed to real, industrial atmospheres, because of the presence of sulfur-bearing corrodents in industrial environments. An important variable in salt spray testing is the position of the surface to be tested. Whereas the surface of test panels is specified to be 15—30° from the vertical (40), when salt spray testing chromated zinc-plated specimens, this range has appeared excessive (41). 

The hydrostatic test is, in one sense, a method of examination of a vessel. It can reveal gross flaws, inadequate design, and flange leaks. Many beheve that a hydrostatic test guarantees the safety of a vessel. This is not necessarily so. A vessel that has passed a hydrostatic test is probably safer than one that has not been tested. It can, however, stiU fail in service, even on the next appheation of pressure. Care in material selection, examination, and fabrication do more to guarantee vessel integrity than the hydrostatic test. 

If the test is to be a guide for the selection of a material for a particular purpose, the limits of controlhng factors in service must be determined. These factors include oxygen concentration, temperature, rate of flow, pH value, and other important characteristics. 

Choices of alternative materials. Corrosion probes are carefully chosen to be as close as possible to the alloy composition, heat treatment, and stress condition of the material that is being monitored. Care must be taken to ensure that the environment at the probe matches the service environment. Choices of other alloys or heat treatments and other conditions must be made by comparison. Laboratory testing or coupon testing in the process stream can be used to examine alternatives to the current material, but the probes and the monitors can only provide information about the conditions which are present during the test exposure and cannot extrapolate beyond those conditions. 

Small variations in service conditions may appreciably affect corrosion resistance. Choice of materials is tlierefore guided wherever possible by a combination of experience and laboratory and site tests. 

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