Issues regarding the use of Q345R material in humid hydrogen sulfide environments
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This post was last edited by maopian001 on 2017-2-8 08:21. There has long been considerable debate regarding whether Q345R is suitable for use in environments with wet hydrogen sulfide. I have recently been working on the design of surface facilities for oil and gas fields in such environments, and based on my experience, I would like to share my personal views for discussion. 1. Can Q345R indeed be used to resist SSC in a wet hydrogen sulfide environment? My personal opinion is that it is acceptable, for the following reasons: a According to clause A.2.2.2 of Appendix A to NACE 0175-2, it is permissible to use materials from Group 1 and Group 2 of P No.1 under the ASME codes for steel used in pressure vessels. As is well known, Q345R is included in ASME’s material catalog, classified under Group 2 of P No.1; therefore, for this reason, I personally believe that from the perspective of the NACE 0175 standard, Q345R is suitable for use. That is one reason. b According to clause 7.5 of SH3075, the yield strength specified in the material standards shall not exceed 355 MPa. Please pay special attention: what is mentioned here is the yield strength specified in the material standards, not the actual measured yield strength of the material – these are two completely different concepts. Many people often use the value of 355 MPa to evaluate Q345R, but I believe this is unreasonable. On the contrary, the standard specification for Q345R specifies a yield strength of 345 MPa; therefore, from the perspective of Chinese standards, Q345R is also suitable for use. That’s the second point. c The specifications issued by Shell in the Netherlands, document 30.10.02.17_Spec_2013-02_A00-WET H2S REQUIREMENTS FOR DOWNSTREAM PRESSURE VESSELS AND PIPING, specify that Q345R as defined in Chinese standards can be used in environments with wet hydrogen sulfide. Foreign engineering companies pay great attention to the safety of their systems; I believe they included Q345R on the approved list after careful consideration rather than making a hasty decision. This is the third point. 2. Effects of excessive Mn content in Q345R: According to GB713, the Mn content in Q345R ranges from 1.2 to 1.7, while clause 7.6.2 of SH3075 specifies that the upper limit for Mn content shall not exceed 1.35. Therefore, many people consider the upper limit for Mn content in Q345R to be too high, and thus it is not suitable for use in environments with wet hydrogen sulfide. Why is it necessary to control the Mn content in fact? This is because Mn reacts with S in steel to form the MnS impurity, which can easily be elongated during rolling, leading to segregation. These segregations provide a trap for the aggregation of hydrogen molecules. When the aggregation of hydrogen molecules exceeds a certain level, hydrogen bubbles HB and hydrogen-induced cracking HIC occur. At the same time, due to the tensile stress present in pressure vessels, these cracks can very easily develop into stress-guided hydrogen-induced cracks under the influence of that stress, namely SOHIC. So, in my opinion, the purpose of controlling the Mn content is mainly to control HIC, HB, and SOHIC. 3. What determines a material’s resistance to SSC? According to the NACE0175 standard, I personally believe the key factor is controlling the hardness values of the base metal, weld, and heat-affected zone. Hardness values are easy to measure, and there is a certain conversion relationship between them and the mechanical properties of materials such as tensile strength; the higher the hardness, the greater the tensile strength, and the poorer the plasticity of the material. Poor plasticity means that cracks are more likely to form, creating crack sources that can give rise to SSC cracks. The above are my personal views; I welcome fellow netizens to discuss them. Furthermore, the relevant departments should conduct some investigations into the use of Q245R and Q345R in wet hydrogen sulfide environments, and prepare a report that can be made public, so that users can have an understanding of how these materials are used.
:lol learned*:lol
http://bbs.hcbbs.com/thread-842892-1-1.html
I’ve seen that post; I have reservations about some of the views expressed in it. It seems like no proper explanation was given – it’s just a simple copying of standards
Are your personal opinions applied in your actual engineering designs? Reactions in related posts reflect the phenomenon that \"since the standards do not explicitly prohibit it, it is not used in actual projects\"; perhaps this is the gap between theory and practice!
Sinopec’s Southwest Branch once applied Q345R in molecular sieve towers, which are still devices subject to fatigue loads and thus have a higher risk factor.
Collecting more such project examples will make it more persuasive! After all, each design institute has its own set of experiences and design guidelines, making it difficult to standardize things unless standards and regulations specify otherwise.
We have used it. But in environments with a relatively low H2S content.
The standards permit the use of Q345R; it’s merely a matter of people interpreting the yield strength specified in the standards as the actual measured yield strength, which is why Q345R cannot be used. The fault really cannot be laid at the feet of the standards
This post was last edited by xlxuiin on 2017-2-7 08:56. Regarding this issue, you can consult the Standards Approval Committee for an authoritative explanation. This is a common phenomenon; it’s not something that a few individuals have “misinterpreted” – it’s simply that the standards are being applied to their minimum level.