Corrosion testing field tests

The literature contains many references to the use of notched, as opposed to pre-cracked or plain, specimens in laboratory studies of stress corrosion, for reasons of improved reproducibility, inability to crack plain specimens under otherwise identical conditions or ease of measuring some parameter such as crack growth rate when the crack location is predetermined. However, the developments in fracture mechanics (see Section 8.9), have resulted in a whole new field of stress-corrosion testing involving the use of specimens... 

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 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... 

These considerations will significantly affect the location of test specimens in field testing. It is clearly important to ensure that the conditions of exposure are accurately known so that the corrosion test results may be interpreted with respect to the end-use requirements. 

Two civil engineering operations require particular attention when soil corrosion tests in the field are required. These are (1) the use of reinforced earth structures in which the corrosion conditions will differ from those at... 

Direct shear test of soils under consolidated drained conditions pH of soil for use in corrosion testing Field measurement of soil resistivity using the Wenner four-electrode method Optimum S03 in portland cement... 

In SNF corrosion tests, there has been a tendency to use the release of more soluble species Tc, Cs, and Mo as markers for fuel corrosion (Finn et al. 2002). As none of these elements are present in the U02 matrix, this approach may not reveal the actual fuel matrix corrosion rate. Furthermore, short-term leaching tests may not expose possible diffusion-limited (tl/2) release of gap and grain boundary species and assume excessive rates of reaction based on initial fast release rates. The microstructure, radiation field, and composition will change over time, so that tests carried out on fuel today may not be relevant to fuel behaviour 300 to 1000 years from now, once the high p-,y-field has decayed. 

Each formulation will be tested for performance both in the laboratory and in the field before being offered for sale. Many standard scaling/corrosion test procedures are available. 

It is preferable to carry out laboratory corrosion tests and to validate the data with service tests for the selection of materials. It is needless to note that the chosen test method be reliable and cost effective. Some of the test methods in use in industry are service tests, field tests, laboratory tests, and rapid electrochemical methods such as potentiodynamic polarization, linear polarization, electrochemical impedance and electrochemical noise. 

The preferred order of corrosion testing and its reliability is service tests > field tests > laboratory tests. It is not always possible to carry out service tests and hence it is recommended that coordinated corrosion testing involving a combination of (i) laboratory test and field test or (ii) rapid electrochemical tests and weight loss, or any other combination that is suitable be carried out. 

Laboratory corrosion tests are conducted in order to obtain information on the interaction of a metal with a particular environment. The tests are generally designed to simulate some field situation. Studies in the laboratory are either aimed at obtaining data in a more convenient way and in a shorter time than on-site determinations or are to provide information, either mechanistic or simulated use, before field application. Final testing should therefore correlate closely to the results obtained from field studies [31]. In devising tests, detailed consideration of their applicability is necessary. Short-term laboratory tests are always a compromise and this should be borne in mind when interpreting results. The number and diversity of test results are such that it is only possible to give a brief description of the more common tests. 

If suitable field sites are not available or lack controlled conditions, then corrosion tests must be conducted in the laboratory. Cabinets are constructed in which the atmosphere is controlled and high humidity and temperature can be used to help accelerate the tests. Marine environments are simulated by salt spray and industrial environments by sulphur dioxide or nitrogen dioxide. Figure 18 shows a salt-spray cabinet and the arrangement of test panels. Periodic changes of temperature within the cabinet can be used to simulate night and day. Addition of other aggressive salts or acid into the sprayed solution is further used to accelerate the test. 

The main source of sulfate in automobile poultices from aggressive northern sites is acid deposition. Road salts introduce both sodium chloride and calcium chloride. However, because of wet/dry cycles, the chemistry of the poultices is complex, involving the formation of calcium sulfate and the depletion of nitrate and chloride ions with a reduction in acidity. Thus corrosion tests based on the analysis of solubles within a poultice at any one time may not reproduce field results the history of the poultice is important. 

The high levels of calcium sulfate in Montreal are indicative of the heavy use of road salts, especially calcium chloride, and of the acid deposition that affects that area. Field corrosion tests showed how aggressive this environment can be even when the solution can quickly run off and evaporate lab tests indicate that after dying out and reacting with calcium chloride, the acid deposition may no longer be important to the corrosion process unless it is renewed. 

Welding results in a metallurgical discontinuity with different microstructures than the parent metal. Mechanical properties of the weld metal usually differ. Even with PWHT, weldments retain a residual stress field. Heat affected zones often contain a coarsened grain structure and/or hard spots. Corrosion testing of the welds may be a critical part of the testing program. 

Schedule 40, 347 SS, 4-inch pipe, a 500-gallon-per-minute sodium pump, a corrosion test section, and a 35-gallon expansion tank. Each and every part was electropolished, pipe ends were taped dust-tight before welding, inert arc gas back welds were made, and every effort was made to complete, in the field, a chemically clean sodium system. Figure 22 shows the dirty sodium surface which resulted after clean sodium was filled into the loop. This experience demonstrated very conclusively the importance of being practical in sodium system construction. 

ISO 8565 1992. Metals and alloys - Atmospheric Corrosion Testing - General Requirements for Field Tests. Geneva, ISO Copyright Office, 1992. 

To obtain a properly formulated paint, testing has to be carried out in different stages (Chaps. 9 and 10) weathering and corrosion tests, application tests, field trials that test in-use behavior, and durability. The paints can only be used commercially when they have passed these tests. 

In atmospheric corrosion testing, it is customary to perform tests in special climate chambers in addition to field tests. The tests are used for comparison but are also valuable for determining the behavior of anticorrosive films and coatings. The conditions used to obtain the appropriate atmospheres, constant or alternating condensed water climates, with and without the presence of such additional substances as sulfur dioxide and salt spray, and at various pH values, are specified in the standards (DIN 50 018 1978 DIN 50 021 1975 ASTM B 117-85 1985 ASTM G 87-84 1984 ASTM G 91-86 1986 ASTM G 85-85 1985). 

An alkyd resin containing less than 1% PANI was examined for its ability to protect carbon steel against aqueous corrosion. In field tests, in urban and marine environments, as well as in accelerated laboratory tests, the presence of PANI in the alkyd resin improved the corrosion protection of carbon steel and also the degradation resistance of the coating [214]. 

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