Hydrogen induced cracking detection
Tianjin Rong Da Testing Co., Ltd. contact: Wang Jingfu
Cell phone: 13102238283 QQ:3144667033
Telephone: 022-23892103
Usually, in particular in the corrosive medium, the material in the stress corrosion rate is very small, and are subject to certain tensile stress (can be far less than the yield strength of the material), after a period of time, even a very malleable metal will occur low stress brittle fracture.
When the carbon steel plate used in the welding pressure vessel is working under wet hydrogen sulfide environment, it may suffer from one or more forms of environmental cracking. These cracking include: (1) high hardness weld and heat affected zone sulfide stress corrosion cracking (SSC); (2) hydrogen cracking (HIC) of base metal; (3) stress oriented hydrogen induced cracking (SOHIC).
Test methods: double beam (DB) test TM0177A NACE method, the test standard TM 0103-2011 NACE
Selection of test methods:
1) the anisotropy of mechanical properties and environmental cracking sensitivity is an important parameter. The test specimen may be involved in the rolling direction, the stress direction and the welding direction in the sample, which are related to the items to be considered.
2) the current can affect the cracking sensitivity of different metals. Electrical coupling increased severity of hydrogen in the steel, which can increase the cracking sensitivity of the steel.
3) the test temperature affects the cracking sensitivity. Most laboratory evaluations are carried out in acidic solutions at room temperature and cracking in sensitive steels. However, in some cases, alkaline hydrogen sulfide environment and / or moderate increase in temperature may increase or decrease the efficiency of hydrogen absorption, thereby affecting the sensitivity of steel cracking beyond the expectations of standard laboratory tests.
4) different test methods may not be able to provide the same order of material sensitivity.
(5) the local multi phase properties (such as partial slag inclusion and impurity segregation, and the number and shape of non metallic inclusions) can affect the test results.
6) because a longer immersion time or a larger number of samples may lead to failure of the material below the stress threshold value, it is clear that the threshold value of the cracking sensitivity should be considered.
7) most of the experiments on the cracking phenomena can be expressed by statistics and / or individual variables. Repetitive tests may be required to obtain a representative numerical value, which can represent the performance of cracking resistance in a test environment.
(8) some samples are more suitable than other samples to measure the cracking resistance of the local area (such as near surface or other features, weld area, etc.). In addition, it is possible to obtain the stress data corresponding to the failure time. In other cases, the experimental measurement of internal crack is more desirable and more useful.
9) the full penetration test is more severe than one side exposure test, which can simulate the exposed surface of pressure vessel, pipeline and flow pipeline more directly.
10) most laboratory tests have a relatively short immersion time, which can not be fully used to produce a large degree of cracking in any given steel, but it is sufficient for the comparison of different materials.