This study is a key reason why GMP became popular as an accelerated laboratory corrosion test for steel. In recent years GMP has been replaced by. of the reference specimens in the as-received condition are in Figure 3. The salt fog test used an abbreviated procedure (Table 3) of the standard GMP test. Find the most up-to-date version of GMP at Engineering
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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.
The test duration can be individually tailored to achieve any desired level of corrosion exposure. Also, synergistic effects due to temperature, mechanical and electrical cycling can be comprehended by this test. See Appendix A for typical modifications. Test durations A and B can be used as both QC tests and validation tests depending on the purpose of the test. Test durations C and D or any modified test are to be used for validation and development purposes.
It requires a 16 h work day or an automatic cycling test chamber. Engineering drawings and material specifications that reference this test procedure must specify the test duration, A, B, C or D or the number of test cycles as indicated in Table 1.
Test durations A and B can be used for quality control and validation procedures as appropriate. Longer test durations C and D and tests involving modifications are to be used for validation purposes only. Modifications to the test may or may not attain equivalent levels of mass loss.
A cycle is made up of the daily events or test inputs prescribed in Table 4. A cycle normally requires 1 day to complete. The test duration is dictated by the number of test cycles. A phase is made up of a predetermined number of cycles, 8 cycles constitute 1 phase.
The coupon mass loss values shown in Table 2 are used to verify that the correct amount of corrosion has been produced by the test. The humidity cabinet shall be as specified by GMP and Table 3. Water fog or visible water droplets on parts – continuous after equilibrium is reached. The salt mist solution shall be as specified in Table 3. The solution shall be sprayed as a mist for example, from a plastic bottle onto the test samples and coupons.
The spray nozzle shall be such that the salt solution is atomized into a mist as required. A siphon spray powered by oil-free regulated air or a hand operated pump spray may also be used.
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The quantity of spray applied should be sufficient to rinse away any salt accumulation left from previous sprays. The dryoff environment area shall be maintained with sufficient air circulation to prevent temperature stratification, and also allow thorough drying of the material. The temperature and humidity conditions are shown in Table 3. Test samples shall be representative of production intent. The weight, in milligrams mgshall be recorded and retained for future reference.
This process can be aided by using a commercial grade degreaser prior to methanol or acetone clean. Prior to 5940p of test, prepare the coupon rack with sufficient coupons to monitor the test 4.
The bolt, nut and washers shall be made from a non black plastic material, preferably nylon. Figure 1 shows a completed coupon rack configuration.
GM P Cyclic Accelerated Corrosion Analysis of Nonchromate Conversion – Google Books
The number of coupons required for different test durations are shown in Table 1. If all solid materials are added dryan insoluble precipitate may 9540pp 3. Coupons consist of Four 4 coupon tm are available as shown in Table 2.
The coupons serve to monitor the average general bare steel corrosion produced by the test environment. However, thicker coupon sizes should be used for tests with long durations. Do not intermix different coupon thickness on the same coupon rack. See Table 4 for the steps that comprise the test gk. Repeat the cycle ym as necessary until the test duration requirements are met. At the option of the test requester, the test can be continued throughout weekends to decrease the over all test time.
The mist application occurs while the samples and coupons are in the ambient environment. Wipe the coupons free of grit and weigh to determine the coupon mass loss using the formula: Refer to Table 2 for targeted mass loss values, in milligrams, for various test durations as a function of the coupon’s original thickness.
Coupon mass loss targets for every phase are not included in Table 2. To check test progress and assure that the test is being run correctly, assume a gk corrosion rate. If the actual mass loss does not coincide with the targeted values listed in Table 2 the test should be repeated.
Also, the reasons why the targeted value s was not obtained should be investigated and corrected before resuming the test. The test ym s shall be inspected for corrosion and photographed at the end of predetermined cycles. At 9540 end of test the samples shall be rinsed with fresh tap water and allowed to dry before evaluating. One 1 test cycle is equal to 24 h, 1 phase is equal to 8 cycles. The test can be 99540p at any time with the understanding that 24 h constitutes 1 cycle.
If gravelometer exposure is required, test samples not coupons may be exposed to gravelometer testing per GMP before or during exposure. If specimen scribing is required, on either test panels or parts, follow the methods described in GMP. This method also includes measurement of corrosion creepback from a scribe line, and describes how to evaluate corrosion formation in unscribed areas.
GMP | Standards | Ascott Analytical
These methods should be used when reporting test results unless stated otherwise on drawings or agreed upon by test requestor and testor. In addition to the sample data and test results, reports must indicate the total number of cycles run, any modifications to the test see Appendix Athe Equipment and Test Record Form Appendix B and should include photographic documentation and the coupon mass loss values. This method may involve hazardous materials, operations and equipment.
This method does not propose to address all the safety problems associated with its use. It is the responsibility of the user of this method to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use. Humidity ramp times between the ambient and wet condition and between the wet and dry conditions are critical to test acceleration this is because corrosion rates are highest during this transition period.
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. If a test is conducted with ramp times different than described above, the number of cycles to reach coupon mass loss targets may increase or decrease. 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.
Corrosion coupons shall be removed and analyzed after each phase throughout the test to monitor the corrosion. To analyze coupons remove 1 coupon from each end of the rack and prepare for weighing and mass loss determination. This standard was written by a task group and approved by the Letter Ballot Committee in February The latest revisions include: This procedure supersedes any old procedures that may have referenced an “A” or “B” Test Method Method A is eliminated.
These procedure modifications are based on field knowledge combined with engineering judgment to enhance the test’s ability to predict field performance. The test is generally made up of 3 shifts: The ambient shift can be modified to include additional test inputs such as dust, grit sprays, mechanical cycling, electrical cycling, thermal inputs, grayelometer and acid rain spray. Ambient Soak 8 h. Expected test duration to evaluate functional corrosion is 10 phases.
Typically no modifications of this shift. If possible, mount test specimens in a production representative orientation simulating onvehicle inputs e. Use Option IV – for door detents without weatherseal protection Use Option VI – for door detents with weatherseal protection 1 test cycle is equal to 24 h, 1 phase is equal to 8 cycles. Typical test duration is 4 cycles for under dash mid to high mount locations and 12 cycles for floorpan low mount locations which approximately equals 10 yearscosmetic corrosion exposure.
Additional options can be customized to specific components or subsystems to increase the ability to conduct validation or development testing. Any option changes not called out specifically in this Appendix must be included on the engineering drawing. Test equipment used shall be documented and include the following information: If a recorder is not in use, written documentation should be provided indicating typical steady state conditions and the ramp times between steady states conditions.
Modify a garden duster to accept an air line connection where the manual pump lever is located remove the manual pump lever and attach a fitting to accept the air line. Garden dusters with an 8 mm diameter hole for dust application are recommended to achieve the appropriate level of dust application. Garden dusters from the following manufacturers could be modified: Hudson Sprayer, Hudson Mfg.