GMW14872 PDF

Search for: Corrosion Testing Standards The test standard summaries are for general guidance only. Though believed to be accurate at the time of writing, this may change over time. So this information should not be used as a substitute for referring to a complete test standard, at an appropriate revision level. In this context they can be considered to be equivalent and interchangeable terms. GMW Accelerated Corrosion Test General Motors This is an accelerated laboratory corrosion test method that can be used to determine the corrosion resistance of automotive assemblies and components. It is said to be effective for evaluating a variety of corrosion mechanisms including general, galvanic, crevice etc.

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GMW Cyclic Corrosion Laboratory Test durability , development testing, and quality control testing, for all global environmental regions refer to GMW for specific Method and applicable region.

The basic exposures for cosmetic corrosion are found below in exposures A through C. All corrosion mechanisms are accelerated at different rates on test. Completing the test may not ensure that a component passes the functional requirement. A comprehensive failure mode analysis must be conducted to ensure all failure modes are considered and life expectancy is met.

Note: In the event of conflict between the English and domestic language, the English language shall take precedence. This procedure describes an accelerated laboratory corrosion test method to evaluate assemblies and components. The test procedure provides a combination of cyclic conditions salt solution, various temperatures, humidity, and ambient environment to accelerate metallic corrosion.

The procedure is effective for evaluating a variety of corrosion mechanisms, such as general, galvanic, crevice, etc. Also, synergistic effects due to temperature, mechanical and electrical cycling along with other stresses can be comprehended by this test.

See Deviations Section, which after the Appendices, for typical modifications. One 1 test cycle is equal to 24 h. A cycle is made up of the daily events or test inputs illustrated in Appendix A, Figure A1. A cycle normally requires one 1 day to complete. The test exposure is dictated by a targeted coupon mass loss. A target range for the number of cycles necessary to meet the required mass loss is provided in Appendix A, Table A1.

The coupon mass loss values are used to verify that the correct amount of corrosion has been produced by the test. In addition to meeting mass loss requirements, the test must be conducted such that the number of cycles required to meet coupon mass loss requirements falls within the specified range.

SAE 3 Resources 3. Laboratory controlled ambient conditions. During steam generated humidity cycles the tester must insure that visible water droplets are found on the samples to verify proper wetness. The solution shall be sprayed as an atomized mist, and should be sufficient to rinse away any salt accumulation left from previous sprays. Suitable application techniques include using a plastic bottle, or a siphon spray powered by oil-free regulated air to spray the test samples and coupons.

Coupons serve to monitor the average general bare steel corrosion produced by the test environment. Coupons consist of The coupons shall be secured to an aluminum or nonmetallic coupon rack with fasteners as shown in Appendix A, Figure A3 and Figure A4.

The bolt, nut and washers shall be made from a non-black plastic material, preferably nylon. Appendix A, Figure A4 shows a completed coupon rack configuration. The number of coupons recommended for different test durations are shown in Appendix A, Table A2. Test samples shall be representative of production intent.

The apparatus shall include provisions for a supply of suitably conditioned compressed air and one or more nozzles for fog generation. The nozzle or nozzles used for the generation of the fog shall be directed or baffled to minimize any direct impingement on the test samples. At least 2 clean fog collectors shall be placed within the exposure zone so that no drops of solution from the test specimens or any other runoff source shall be collected.

The collectors shall be placed in the proximity of the test specimens, one nearest to any nozzle and the other farthest from all nozzles. Collection rates for each 80 cm2 of horizontal collection area should be in the range of 0.

Fog collection rates may be adjusted within this range as necessary to meet mass loss target rates. Suitable collecting devices include glass or plastic funnels with the stems inserted through stoppers into graduated cylinders. Funnels with a diameter of 10 cm have an area of about 80 cm2. Where samples cannot be read immediately upon completion of the humid stage, closed cell foam balls can be used in combination with the collections funnels i.

The apparatus shall consist of the chamber design as defined in ISO During wet-bottom generated humidity cycles the tester must insure that visible water droplets are found on the samples to verify proper wetness.

Calcium Chloride must be reagent grade. Sodium Bicarbonate must be reagent grade e. If all solid materials are added dry an insoluble precipitate may result. Salt solution makeup calculator for the appropriate amount of sodium chloride, calcium chloride, sodium bicarbonate, and water examples are shown in Appendix B, Figures B1 through B3.

Additional contaminants dust, grit, poultice, and exhaust condensate called out in the Deviation Section are defined in Appendix C through Appendix F. Corrosion coupons should be cleaned with methanol or acetone solution and accurately weighed prior to use. The weight, in grams g , shall be recorded and retained for future reference.

If coupons are not used immediately they should be stored such that they are corrosion free at the start of test. This process can be aided by using a commercial grade degreaser prior to methanol or acetone clean. Prior to start of test; prepare the coupon rack with sufficient coupons to monitor the test.

The exact location of each coupon on the rack shall be identified and recorded using the prestamped numbers for reference as illustrated in Appendix A, Figure A4. Allow a minimum 5 mm spacing between the coupons and the rack surface.

All coupons shall be secured vertically with no more than 15 degree deviation from vertical and must not contact each other. The coupon rack shall be placed in the general vicinity of the test samples being tested, such that the coupons receive the same environmental exposure as the test samples.

Note: Coupons are test monitoring devices and should not be exposed to additional stresses which may be added to the base test i. Deviations from the requirements of the procedure shall have been agreed upon by test requestor. Such requirements shall be specified on part drawings, test certificates, reports, etc. Repeat the cycle daily, as necessary, until the test exposure requirements are met.

At the option of the test requester, the test can be continued throughout weekends to decrease the over all test time provided that the number of cycles and mass loss requirements are met. The quantity of spray applied should be sufficient to visibly rinse away salt accumulation left from previous sprays. The first salt mist application occurs at the beginning of the ambient stage.

Each subsequent salt mist application should occur approximately an hour and a half after the previous application in order to allow adequate time for test samples to dry. Note: If gravelometer exposure is required, test samples not coupons may be exposed to gravelometer testing per GMW before or during test exposure. Humidity ramp times between the ambient and wet condition and between the wet and dry conditions can have a significant effect on test acceleration this is because corrosion rates are highest during these transition periods.

Typically, the time from ambient to the wet condition should be approximately 1 h and the transition time between wet and dry conditions should be approximately 3 h. These ramp times can be adjusted to increase or decrease test acceleration in order to meet targeted mass loss. Test acceleration can be optimized and tracked by using standard corrosion coupons as monitoring devices.

Ramp time is to be included as part of the specified exposure period. This method should be used when reporting test results unless stated otherwise on drawings or agreed upon by test requestor and tester.

At the end of test the samples shall be rinsed with fresh tap water and allowed to dry before evaluating. To analyze coupons remove 1 coupon from each end of the rack, clean to prepare for weighing, and an average mass loss determination. Note: Although not preferred corrosion by-product removal by chemical cleaning per ISO may be used. Testing should be conducted as necessary to achieve necessary coupon mass loss. The number of cycles required to achieve required mass loss must meet that defined in Appendix A, Table A1.

Coupon mass loss targets corresponding to incremental test exposures are not included in Appendix A, Table A1. The processes defined in section 4. Corrosion mass loss should increase consistently between documented exposure values. If the actual mass loss does not fall within the targeted range for the specified exposure s as listed in Table A1 then the test should be repeated. Also, the reasons why the test did not fall within the target range should be investigated and corrected before resuming the test.

If scribing is required, on test samples, follow the method described in GMW This method includes measurement of corrosion creepback 5 Data 5.

Salt solution reference Appendix B. Coupon mass loss reference section 4. Acceptance criteria shall be specified within engineering documentation which includes: Material Specifications, Subsytem Technical Specifications, Component Technical Specifications, and Part Drawings.

Coupon mass loss values are to be recorded after each set of a predetermined number of cycles typically 5 and at the completion of the desired test exposures.

Data may be plotted and used to evaluate conformance to mass loss requirements using charts like the examples found in Appendix G, Figure G1 and Figure G2. Test reports should include the sample data and test results, number of cycles run, coupon mass loss data and any deviations to the test. If a recorder is not in use, written documentation should be provided indicating typical steady state conditions and the ramp times between steady state conditions.

If information does not change from test to test, documentation of a representative test will be acceptable. All the specified information will be required if test results are in question.

Test Solution. The following information shall be recorded and available upon request. All specified information will be required if test results are in question.

Example 4: For a door hinge mounted outside the weatherstrip in a global region specified in Method SL cosmetic and functional. This method does not propose to address all the safety problems associated with its use. It is the responsibility of the user of the method to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.

Not Applicable. This standard originated in November , replacing GMP.

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Corrosion Testing Standards

GMW Cyclic Corrosion Laboratory Test durability , development testing, and quality control testing, for all global environmental regions refer to GMW for specific Method and applicable region. The basic exposures for cosmetic corrosion are found below in exposures A through C. All corrosion mechanisms are accelerated at different rates on test. Completing the test may not ensure that a component passes the functional requirement. A comprehensive failure mode analysis must be conducted to ensure all failure modes are considered and life expectancy is met. Note: In the event of conflict between the English and domestic language, the English language shall take precedence.

CONDICA PREZENTA PDF

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An accelerated laboratory corrosion test to evaluate automotive coatings and components. Introduction In the American Iron and Steel Institute, in conjunction with a Committee of the SAE, conducted a study of existing cyclic corrosion tests in order to establish the best methods of predicting the performance of materials used in automotive applications. Twenty established corrosion test procedures were included within the study. The process itself comprised of undertaking tests on 10 different materials with each procedure, the results were compared to results gathered through real World exposure from 10 locations around the globe, undertaking the tests with identical materials. The procedures were judged on: Their ability to replicate the rank order of coatings performance in the real World. Method Specimens being tested are exposed to a multi-stage changing environment that is composed of three distinctive cycles, these stages can be varied depending on the nature of the specimen undertaking the test, for further information please refer to the full GMW standard. During this period salt solution is sprayed directly on to the test samples 4 times, for long enough to thoroughly wet them.

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