Corrosion acceptance testing

Corrosion testing is used to select materials of construction, and to monitor the performance of selected materials of construction in service. Availability of the materials should be considered when developing corrosion test programs. Corrosion acceptance testing is performed to ensure that specific corrosion-resistant alloys are manufactured without impairing their corrosion resistance. 

A producer who has supplied a specific nickel alloy for many years will have developed the thermal and mechanical processing know-how for the alloy. Exp>erienced producers rely on statistical process control, coupled with sample testing to qualify their alloys. New producers may meet the ASTM compositional sp>ecifications for the alloys, but do not necessarily understand the thermal and mechanietd processing needed for creating the best metallui gical condition in the alloy. For new producers, corrosion acceptance testing of various product forms made from each heat of the alloy is usually necessary. 

Sa.lt Spray Tests. One of the older accelerated corrosion tests is the salt spray test (40). Several modifications of this imperfect test have been proposed, some of which are even specified for particular appHcations. The neutral salt spray test persists, however, especially for coatings that are anodic to the substrate and for coatings that are dissolved or attacked by neutral salt fog. For cathodic coatings, such as nickel on steel, the test becomes a porosity test, because nickel is not attacked by neutral salt fog. Production specifications that call for 1000 hours salt spray resistance are not practical for quahty acceptance tests. In these cases, the neutral salt spray does not qualify as an accelerated test, and faster results from different test methods should be sought. 

In the absence of any other relevant information, it is essential to obtain this via an internationally recognized corrosion/irritation test before proceeding to a rabbit eye irritation test. This must be conducted in a staged manner. If possible, this should be achieved using a validated, accepted in vitro skin corrosivity assay. If this is not available, then the assessment should be completed using animal tests (see the skin irritation/ corrosion strategy, section 3.2.2). 

A liquid is considered to have a severe corrosion rate if its corrosion rate exceeds 0.250 inch per year (IPY) on steel (SAE 1020) at a test temperature of 130°F. An acceptable test is described in NACE Standard TM-02-69. ... 

There are other equivalent tests which can show that the vessel is mechanically strong. For pumps, integrity data would involve the frequency of seal repairs, bearing repairs, nature and intensity of vibration, plugging, and corrosion problems. With the mechanical integrity tests, other data is recorded, such as records of inspections and tests, maintenance procedures, establishment of criteria for acceptable test results, and documentation of inspection results. Preventive maintenance (PM) programs are a big part of the PSM. 

Many protection mechanisms related to ICPs have been proposed in the literature, and in some cases opposing evidence exists. This confusion may be attributed to the wide variations in experimental procedures used (coating type, substrate preparation, corrosive environment, test method). In the following, we just list the main mechanisms that have appeared in the literature. Further details can be found in the review by Spinks et al. [7]. However, the anodic protection mechanism will be discussed at length because it is the most commonly accepted mechanism in previous studies. 

Extensive testing on stainless steel mockups, fabricated using production techniques, has been conducted to determine the effect of various welding procedures on the susceptibility of unstabilized 300 series stainless steels to sensitization-induced intergranular corrosion. Only those procedures and/or practices demonstrated not to produce a sensitized structure are used in the fabrication of RCPB components. The ASTM standard A 708 (Strauss Test) is the criterion used to determine susceptibility to intergranular corrosion. This test has shown excellent correlation with a form of localized corrosion peculiar to sensitized stainless steels. As such, ASTM A 708 is utilized as a go/no-go standard for acceptability. 

The current salt spray test, in which the plated specimen is exposed to a spray or fog of sodium chloride solution, is the most widely used accelerated corrosion test for coatings, and various procedures have acceptance tests in standard specifications in numerous countries. Over the years, the procedure has employed sodium chloride solutions of concentrations between 3 and 20 %, sometimes with the addition of hydrochloric acid or hydrogen peroxide. The salt spray test [ASTM B 117, Test Method of Salt Spray (Fog) Testing] has largely fallen into disrepute because of the recognition that its reproducibility and correlation with outdoor exj>osure were often poor. Cyclic salt spray testing as well as alternate electrolytes such as the "prohesion test solution have been found to produce more realistic results. 

The decision to test is usually driven by unusual chemistry such as a new catalyst, reaction components, or reaction conditions. Immersion/mass loss method is primarily used in conjunction with microscopic examination. Process fluids from production or pilot runs are primarily used to best simulate potential corrosion. The test methods are custom designed based, in part, on cost and the ability to obtain sufficient quantities of test fluids, and handle the process conditions. Process conditions are tested outside the process control limits (e.g., temperatures, pH) to better accentuate the corrosion potential. These extremes have to be tempered by the stability of the products in the stream. For wall thicknesses greater than 0.250 in. (6.35 mm), a uniform loss of less than 10 mil/year (0.26 mm/year) is considered structurally acceptable. Signiflcandy lower levels of uniform loss are of concern for product or process contamination issues. Microscopic examination is used to determine potential localized corrosion concerns, such as pitting or stress cracking. Indications of pitting or stress corrosion in stamped areas of the coupon are of particular concern. U-bend tests are rarely used because of insufflcient test fluid quantities and availability. 

With halogenated solvents, only supernatant (immiscible) water can be efficiently removed, and all water reacts with the solvents . Management of the retained water level devolves to management of added stabilizers which sequester the reartion products of the water and the halogenated solvent — corrosive mineral acids. So the answer to the question above with halogenated solvents is to use acid acceptance test kits and always maintain the positive presence of at least 0.2% NaOH equivalent . ... 

The world-accepted test for corrosion resistance is the SINTEF test (Fig. 2.73a). A lab reduction cell [151-154] comprises graphite crucible. On the bottom of the crucible there is a TiB2-coated cathode, the anode is in the upper part, and the tested SiC rods, dipped into the melts of aluminium and bath, are exposed to the bath, aluminium, and oxygen in the presence of vapors. The lab reduction cell is in the furnace. The corrosion resistance is determined by the volume change (Fig. 2.73b). The inventors [151] made a corrosion resistance scale, determined by the volume loss of the samples (Tables 2.16). 

Summary of validated alternative methods for skin corrosion, accepted by regulatory authorities in EU legislation (Annex V of the Dangerous Substances, Directive 67/548/EEC) and in the OECD testing guidelines (TG) for chemicals... 

A significant effort has been made over the past quarter century to develop effective techniques to test and assess the effect of corrosion on the performance and life of electronic devices. Such techniques are desired for two specific uses (a) as a means of rapidly characterizing product quality during manufacturing (acceptance testing) and (b) to provide customers and users with an accurate estimate of expected service life. In this context. 

Apart from added stabilizers, commercial grades of trichloroethylene should not contain mote than the following amounts of impurities water 100 ppm acidity, ie, HCl, 5 ppm insoluble residue, 10 ppm. Free chlorine should not be detectable. Test methods have been estabUshed by ASTM to determine the following characteristics of trichloroethylene acid acceptance, acidity or alkalinity, color, corrosivity on metals, nonvolatile-matter content. 

ASTM has estabhshed standard test methods to determine acid acceptance, acidity, alkalinity, color, corrosivity to metals, nonvolatile matter content. 

Substituting one alloy for another may be the only viable solution to a specific corrosion problem. However, caution should be exercised this is especially true in a cooling water environment containing deposits. Concentration cell corrosion is insidious. Corrosion-resistant materials in oxidizing environments such as stainless steels can be severely pitted when surfaces are shielded by deposits. Each deposit is unique, and nature can be perverse. Thus, replacement materials ideally should be tested in the specific service environment before substitution is accepted. 

In recent years it has been regarded as somewhat passe to refer to Sir Humphrey Davy in a text on cathodic protection. However, his role in the application of cathodic protection should not be ignored. In 1824 Davy presented a series of papers to the Royal Society in London in which he described how zinc and iron anodes could be used to prevent the corrosion of copper sheathing on the wooden hulls of British naval vessels. His paper shows a considerable intuitive awareness of what are now accepted as the principles of cathodic protection. Several practical tests were made on vessels in harbour and on sea-going ships, including the effect of various current densities on the level of protection of the copper. Davy also considered the use of an impressed current device based on a battery, but did not consider the method to be practicable. 

The effects of corrosion on other properties need similar direct assessment in many cases. However, in the absence of accepted standard tests the BS, DIN, ISO tests for laboratory glassware are often used. At the present time, the British Standard BS 3473 Methods of testing and classification of the chemical resistance of glass used in the production of laboratory glassware is being re-issued in six parts, of which the first five parts are identical to recently revised ISO test procedures. There are also corresponding DIN tests in some cases which are very similar. The current situation is ... 

---