4.1 These test methods describe laboratory tests for comparing the resistance of stainless steels and related alloys to the initiation of pitting and crevice corrosion. The results may be used for ranking alloys in order of increasing resistance to pitting and crevice corrosion initiation under the specific conditions of these methods. Methods A and B are designed to cause the breakdown of Type 304 at room temperature.

4.2 The use of ferric chloride solutions is justified because it is related to, but not the same as, that within a pit or crevice site on a ferrous alloy in chloride bearing environments (1, 2).3 The presence of an inert crevice former of consistent dimension on a surface is regarded as sufficient specification of crevice geometry to assess relative crevice corrosion susceptibility.

4.3 The relative performance of alloys in ferric chloride solution tests has been correlated to performance in certain real environments, such as natural seawater at ambient temperature (3) and strongly oxidizing, low pH, chloride containing environments (4), but several exceptions have been reported (4-7).

4.4 Methods A, B, C, D, E, and F can be used to rank the relative resistance of stainless steels and nickel base alloys to pitting and crevice corrosion in chloride-containing environments. No statement can be made about resistance of alloys in environments that do not contain chlorides.

4.4.1 Methods A, B, C, D, E, and F were designed to accelerate the time to initiate localized corrosion relative to most natural environments. Consequently, the degree of corrosion damage that occurs during testing will generally be greater than that in natural environments in any similar time period.

4.4.2 No statement regarding localized corrosion propagation can be made based on the results of Methods A, B, C, D, E, or F.

4.4.3 Surface preparation can significantly influence results. Therefore, grinding and pickling of the specimen will mean that the results may not be representative of the conditions of the actual piece from which the sample was taken.

NOTE 1: Grinding or pickling on stainless steel surfaces may destroy the passive layer. A 24 h air passivation after grinding or pickling is sufficient to minimize these differences (8).

4.4.4 The procedures in Methods C, D, E, and F for measuring critical pitting corrosion temperature and critical crevice corrosion temperature have no bias because the values are defined only in terms of these test methods.

NOTE 2: When testing as-welded, cylindrical, or other non-flat samples, the standard crevice formers will not provide uniform contact. The use of contoured crevice formers may be considered in such situations, but the use of a pitting test (Practices A, C, or E) should be considered.

1. Scope

1.1 These test methods cover procedures for the determination of the resistance of stainless steels and related alloys to pitting and crevice corrosion (see Terminology G193) when exposed to oxidizing chloride environments. Six procedures are described and identified as Methods A, B, C, D, E, and F.

1.1.1 Method A—Ferric chloride pitting test.

1.1.2 Method B—Ferric chloride crevice test.

1.1.3 Method C—Critical pitting temperature test for nickel-base and chromium-bearing alloys.

1.1.4 Method D—Critical crevice temperature test for nickel-base and chromium-bearing alloys.

1.1.5 Method E—Critical pitting temperature test for stainless steels.

1.1.6 Method F—Critical crevice temperature test for stainless steels.

1.2 Method A is designed to determine the relative pitting resistance of stainless steels and nickel-base, chromium-bearing alloys, whereas Method B can be used for determining both the pitting and crevice corrosion resistance of these alloys. Methods C, D, E, and F allow for a ranking of alloys by minimum (critical) temperature to cause initiation of pitting corrosion and crevice corrosion, respectively, of stainless steels, nickel-base and chromium-bearing alloys in a standard ferric chloride solution.

1.3 These tests may be used to determine the effects of alloying additives, heat treatment, and surface finishes on pitting and crevice corrosion resistance.

1.4 The values stated in SI units are to be regarded as standard. The values given in parentheses after SI units are provided for information only and are not considered standard.

1.5 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.

1.6 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.

Test Item 测试名称: ASTM G48 Testing in ferric chloride solution allows a quick assessment of pitting corrosion resistance of stainless steels 不锈钢及有关合金三氯化铁点蚀和缝隙腐蚀标准

Test Requirements 测试要求：

Test Method C
Test Method D

Sample Size 样品数量 / 送样规格：25mm x 50mm

由于C、D法均为临界温度检测，需要首先根据样品成分计算样品的CPT和CCT，然后每隔5℃进行一次实验，直至不发生点蚀或缝隙腐蚀。每个温度需要测试3~5平行样。因此总的样品数为：N= 所测温度数 x 3~5，一般样品至多需要15个测温点，总样品数45~75个，两个方法共计90~150个样品。

ASTM G48 标准中关于样品表面的要求，如果您是机加工切割获得表面，应通过砂纸磨制去除由于机加工引起的变形层，以避免影响腐蚀试验结果，如果您无法进行预磨，我们可以协助进行，但请您注明样品待测表面的前期处理工艺。ASTM G48 Method D中需要在样品中心钻孔以便进行缝隙腐蚀夹具的加持，可以由我们根据我们的夹具进行加工。/ 7.2 When specimens are cut by shearing, the deformed material should be removed by machining or grinding prior to testing unless the corrosion resistance of the sheared edges is being evaluated. It is good practice to remove deformed edges to the thickness of the material.

Lead Time / TAT (Turn Around Time) 测试周期: 常规服务 regular service 12 weeks。每个温度点的单次检测72小时，加上容器装卸与测量，每周可以进行一个温度点的检测，至多15周可以完成，如需加急（加急费用另计），可以在2个月内完成。

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