Discussion on the Verification Testing of Carbon Content in Components of Ultra-Low Carbon Stainless Steel Pipes

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Discussion on the Verifying Inspection of Carbon Content in Components of Ultra-Low Carbon Stainless Steel Pipes, Engineering Quality Supervision Station of CNPC Dushanzi Petrochemical Branch, Karamay, Xinjiang 833699. Quality and safety accidents caused by potential engineering quality issues in the construction of the petrochemical industry continue to occur despite repeated efforts to prevent them. Problems such as abnormal shutdowns of the equipment, explosions, fires in production, and even construction safety or production accidents resulting in casualties occur from time to time, which undoubtedly serves as a warning to those involved in engineering projects. From the perspective of project quality supervision, this article elaborates in detail on the phenomenon whereby, after construction units conduct verification tests on the contents of the main alloying elements in the components of ultra-low carbon stainless steel pipes in accordance with construction standards, the carbon content of these main alloying elements is not retested, as well as the necessity of adding such verification tests for carbon. 1 The necessity of conducting spectral analysis for random re-inspection of the carbon content in components of ultra-low carbon stainless steel pipes in petrochemical construction. Ultra-low carbon stainless steel refers to austenitic stainless steel with a carbon content of less than 0.03% or ferritic stainless steel with a carbon content of less than 0.01%; it has very low susceptibility to intergranular corrosion, and the carbon content is the key factor in preventing such corrosion. Since at room temperature the maximum mass fraction of carbon that can be dissolved in austenite is 0.02%–0.03%, ultra-low carbon austenitic stainless steels generally do not suffer from intergranular corrosion. With the development of the national economy, there is an increasing number of petrochemical plants being built across the country. Ultra-low carbon stainless steel materials are being used increasingly in pipelines exposed to high temperatures, high pressures, low temperatures, corrosion, and flammable media, and the number of verification tests for such materials during construction is increasing year by year. Between 2004 and 2019, there were at least 6 incidents of equipment explosions and fires within the petrochemical industry resulting from the incorrect use of alloy steel materials. Practice has shown that during the project construction phase, only by conducting a thorough inspection of alloy steel products on-site can potential quality issues arising from the material itself be effectively eliminated. The economic viability of conducting additional random spectral analysis tests for carbon content as part of the incoming inspection of 2 ultra-low carbon stainless steel pipe components: With the development of spectral detection technology, such equipment has become increasingly widespread, and its advantages lie in its sensitivity and speed. Currently, the spectrometers used in the petrochemical industry mainly include direct-reading spectrometers, portable direct-reading spectrometers, and handheld spectrometers. Depending on the required testing requirements, it is divided into qualitative analysis, quantitative analysis, and semi-quantitative analysis. OES analyzers, portable OES analyzers, and handheld spectrometers are used for quantitative analysis, allowing for on-site random inspections and retests of the composition of ultra-low carbon stainless steel pipes. Portable optical emission spectrometers and handheld spectrometers are mainly used at construction sites. The materials used for components of ultra-low carbon stainless steel pipes mainly include: 022Cr17Ni14Mo2, 316L, 00Cr17Ni14Mo2Cu2, 00Cr19Ni10, 304L, 00Cr25Ni22Mo2, etc. During petrochemical construction, the proportion of ultra-low carbon stainless steel pipe components in the total alloy material is small; it is entirely feasible to conduct random spectral analysis tests on the carbon content, and the testing costs are controllable. 3 Scope of verification testing for ultra-low carbon stainless steel pipe components in construction standards: The acceptance specifications commonly used in oil refining and chemical industry projects specify the scope of verification testing for such pipe components: GB50184-2011 Code for Acceptance of Construction Quality of Industrial Metal Piping – For stainless steel pipe components, sampling inspections of the material shall be carried out, and proper labeling must be applied. After the installation of the alloy steel piping system, the material markings should be checked. Inspection method: Visual inspection; spectral analysis or other material reinspection methods may be used if necessary. GB50517-2010 Code for Acceptance of Construction Quality of Petrochemical Metal Piping Projects: For pipes, fittings, flanges (covers) and valves made of nickel-containing low-temperature steel and molybdenum-containing austenitic stainless steel, verification tests for the main alloying metal elements shall be carried out using spectral analysis or other methods. After the installation of chromium-molybdenum alloy steel, nickel-containing low-temperature steel, and molybdenum-containing austenitic stainless steel piping systems, the material identification should be checked; if no identification is present, spectral analysis should be used to verify the material. SH3501-2011 Code for Construction and Acceptance of Steel Piping Projects for Toxic and Flammable Media in the Petrochemical Industry: For pipe components made of nickel-containing low-temperature steel and molybdenum-containing austenitic stainless steel, verification tests on the content of major alloying elements shall be carried out using spectral analysis or other methods in accordance with the provisions of this code. After the pipeline system is installed, the material markings should be checked. When no markings are found on chromium-molybdenum alloy steel, nickel-containing low-temperature steel, and molybdenum-containing austenitic stainless steel, spectral analysis should be used for verification. 4 Reasons for the Failure to Detect Defective Materials in Components of Ultra-Low Carbon Stainless Steel Pipes: Since ultra-low carbon stainless steel is difficult to distinguish from ordinary stainless steel, the codes GB 50184-2011 Code for Acceptance of Construction Quality of Industrial Metal Piping Projects, GB 50517-2010 Code for Acceptance of Construction Quality of Petrochemical Metal Piping Projects, and SH3501-2011 Code for Construction and Acceptance of Steel Piping Projects for Toxic and Flammable Media in Petrochemical Industries do not specify the need for retesting of carbon content in these pipe components. The explanation provided by the standard specification guidelines is that carbon content can be retested when there are doubts regarding the certificate of conformity and the physical markings of ultra-low carbon stainless steel materials. During actual construction, the contractor only conducts random tests to verify the main alloying elements; however, the data obtained from such tests for stainless steel materials such as 316L and 316, or 304L and 304, are identical. For example, in the case of products that have arrived, the 00Cr19Ni10 stainless steel material is replaced with 0Cr18Ni9; when random inspections are carried out in accordance with construction specifications to check the main alloying elements, the material is deemed to be qualified. When substandard products consisting of ultra-low carbon stainless steel pipes with inadequate carbon content are supplied, there is a possibility of missed inspections during the construction process. 5. Experience of the project owner in increasing the proportion of verification tests for alloy steel materials during construction. Since during construction, only random retests are conducted on the major alloying elements in the components of ultra-low carbon stainless steel pipes, with no retesting of the carbon content, there are no instances of defective products resulting from components with unacceptable carbon content. However, Dushanzi increased the proportion of verification tests on alloy steel materials through large-scale projects and major overhauls, and discovered thousands of defective products. This indicates that there are defective products among the pipe components, and it is necessary to conduct additional random inspections for carbon content in ultra-low carbon stainless steel pipe components. The total investment for Dushanzi Petrochemical Company’s 10 million tons per year oil refining and 1.2 million tons per year ethylene production facilities is over 30 billion yuan. There are a wide variety of materials used for process pipelines. The main models of spectrometric testing equipment used in large projects and major maintenance activities include: the SPECTRO LAB M7 and M11 optical emission spectrometers, the ARC-MET930 and ARC-MET8000 devices, as well as the SPECTRO Test3 portable optical emission spectrometers; additionally, there are the Niton XLt898 and XL2 handheld spectrometers. Based on past experience, the Quality Management Center of the Project Command Headquarters of the Dushanzi Petrochemical Branch, the construction entity, required that during the construction of the project involving the expansion and renovation of Dushanzi Petrochemical’s 10-million-ton oil refining facility and the construction of a new 1.2-million-ton ethylene plant, after the petrochemical company conducts verification inspections at its central warehouse and the construction contractor performs verification inspections on alloy steel materials in accordance with construction standards, the Quality Management Center would then commission a third-party testing agency to conduct online spectral testing on 10% of the materials. The Quality Management Center requires that whenever one case of alloy steel products being mistakenly used in place of carbon steel is detected, 100% on-line re-inspection of that manufacturer’s alloy steel products be carried out. Third-party testing agencies inspected 18,310 items and found that 321 products made of alloy steel had been mistakenly labeled as carbon steel products by the manufacturers. Apart from the construction units that were inspected by the project owner and found to have indeed used the wrong material, which voluntarily carried out 100% online spectral testing of the medium and low-alloy steel products, all other general contractors and construction units that were not inspected also conducted 100% online spectral testing of such products as required by the project owner. As a result, thousands of products with the wrong material were identified, ensuring that no medium or low-alloy steel products were used incorrectly in this project. During the major overhauls at Dushanzi Petrochemical Company in 2011 and 2015, 100% spectral testing was conducted on low-alloy steel products from 29 units, including those in the refinery, the old area of the ethylene plant, the new area of the ethylene plant, and the thermal power plant; 160 samples failed the tests. Ultimately, 100% online spectral analysis for alloy steel was implemented, which minimized the risk of serious production safety accidents resulting from the incorrect use of alloy steel grades, thereby providing reliable quality assurance for the long-term operation of the facility. 6 The importance of standardized verification testing for carbon content in ultra-low carbon stainless steel pipeline components. Practice has shown that defective products among alloy steel pipeline components used in the petrochemical industry occur from time to time. After the construction contractor conducts verification tests on the contents of the main alloying elements in the components of ultra-low carbon stainless steel pipes in accordance with the construction specifications, if components with unacceptable carbon content are supplied, failures to detect such issues may occur during the construction process. It is highly necessary to conduct random spectral analysis tests on the carbon content of the components of ultra-low carbon stainless steel pipes during construction, and the testing costs are controllable. The use of defective ultra-low carbon stainless steel pipe components in operating equipment poses significant safety hazards. References: GB 50184-2011 Code for Acceptance of Construction Quality of Industrial Metal Piping Projects ； GB 50517-2010 Code for Acceptance of Construction Quality of Petrochemical Metal Piping Projects ； SH3501-2011 Code for Construction and Acceptance of Steel Piping Projects for Toxic and Flammable Media in the Petrochemical Industry