Issues regarding phosphorus and sulfur content in welding materials as specified in GB/T 150
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Paragraph a) of clause E.2.1.5 in Appendix E of GB150.3 stipulates that for welding materials used in low-alloy steel cryogenic vessels, those whose standard tensile strength of the deposited metal is ≤ 550 MPa shall have a phosphorus content of not more than 0.025% and a sulfur content of not more than 0.012%； For welding materials whose standard minimum tensile strength of the deposited metal is >550 MPa, the phosphorus content shall not exceed 0.020% and the sulfur content shall not exceed 0.010%. Clause 5.1.2.3 of GB/T150.4 stipulates that for welding materials used for low-alloy steel pressure components with a minimum standard tensile strength of more than 540 MPa, or for pressure vessel components operating at temperatures below -40°C, the chemical composition of the weld metal shall be rechecked on a batch basis; the phosphorus content in the weld metal shall not exceed 0.020%, and the sulfur content shall not exceed 0.010%. It seems that these two regulations conflict with each other – how should they be implemented?
According to the GB/T 150 standard, stricter requirements can be applied. That is, for welding materials whose standard minimum tensile strength of the deposited metal is greater than 550 MPa, the phosphorus content must not exceed 0.020% and the sulfur content must not exceed 0.010%. This meets the requirements of Appendix E to GB150.3 as well as the provisions in GB/T150.4, ensuring welding quality and safety. .
Following strict rules is certainly the right approach; the problem is that it seems the main drafters of these two sections worked independently, with no one conducting a unified review of the entire 150-page document, resulting in a lack of rigor. If manufacturing units conduct retesting of welding materials at -40°C only in accordance with 150.4, they may fail to meet the sulfur and phosphorus content requirements specified in Appendix 150.3 for the range of -20 to -40°C.
Meet the high standards. GB/5 150-1~4-2024 was revised separately by different personnel
I understand that the more stringent requirement should be that the lower limit of the tensile strength standard for the deposited metal be greater than 540 MPa for welding materials, rather than 550 MPa. Otherwise, are the requirements between 540 and 550 relaxed?
150.2 Regarding the requirements for welding materials, it is specified that the tensile strength of the deposited metal should be 550 MPa; this means it is suitable for welding steel with a standard tensile strength of 540 MPa, and there is nothing wrong with this description. The key issue is that there are no requirements in 150.4 regarding the welding materials to be used for the pressure-bearing components of containers in the range of -20°C to -40°C, which can lead to problems when manufacturing units choose such welding materials.
These two requirements are not contradictory; the clause in GB150.4 specifies two conditions, and once one of them is met, the selection of welding materials must follow those guidelines. There is an overlap between GB150.3 and GB150.4, and it is sufficient to choose the appropriate welding materials based on the design conditions indicated in the diagram.
Indeed, the requirements for welding materials in the GB/T 150 standard may involve overlapping or missing information in different sections, which can lead to misunderstandings, particularly regarding the requirements for specific temperature ranges and tensile strength values. This situation may lead to the risk of non-compliance when selecting and applying welding materials. To avoid such problems, it is recommended that manufacturers, when selecting welding materials, not only refer to the requirements specified in the relevant standards but also take into account design requirements, operating conditions, and the performance of the welding materials; if necessary, additional material testing or consultation with specialized agencies should be carried out. At the same time, this situation can be brought to the attention of the standards-setting or updating bodies, with a recommendation that they include specific material requirements for such temperature ranges in future standard revisions, in order to enhance the completeness and practicality of the standards. In summary, strictly reviewing the selection and implementation of each process, in line with the actual engineering requirements and safety standards, is key to ensuring the success and safety of the project. .