Inspection of Hydrogen Pipelines in Refining and Chemical Hydrogen Production Units
Posted: 08/23/2023 07:50:47 Hits: 27
3. Research on the failure
3.1 Design aspects
All stainless steel pipes and pipe fittings of this device are ordered according to the detailed engineering design "Comprehensive Material Lists" of the design institute, and the material is 0Cr18Ni10Ti. Conform to design specifications "Design and General Rules of Petrochemical Pipeline Layout" SH3012-2000, "Petrochemical Equipment and Design Specifications of Pipeline Thermal Insulation" SH3010-2000, "Design Specifications of Industrial Metal Pipelines" GB50316-2000. According to the design requirements, the pipe fittings are manufactured in accordance with the SH3408 "Steel Butt Welding Seamless Pipe Fittings" and the GB14976 Stainless Steel Seamless Pipes Conveying Fluid.
Relevant professional technicians of the design institute carefully analyzed and discussed the reducer of the pipeline of the hydrogen production unit, and conclude that the pipeline is made from stainless steel SS321, which will not cause hydrogen corrosion according to the working temperature and working pressure, and conforms to the material selection requirements of "General Rules for Selection of Petrochemical Pipeline Design Equipment". The maximum working temperature of the pipeline is 420°C and the maximum working pressure is 3.5MPa, and according to the calculation formula in the "General Rules for Selection of Equipment for Petrochemical Pipeline Design”, DN300 is obtained after considering the negative deviation and the maximum inner wall thickness is only 7.85mm. According to the design wall thickness of SH3405, SCH40s is selected for the design wall thickness; the maximum inner wall thickness of the elbow after considering the negative deviation of DN400 is only 9.6mm, and the design wall thickness is 13mm; the maximum inner wall thickness of the elbow after considering the negative deviation of DN500 is only 14.2mm, and the design wall thickness is 15mm. There is no problem in the design of wall thickness; the water injection position is based on the equipment drawings and technology provided by the desuperheater manufacturer. There is no problem. Chloride ions should be mainly considered for the corrosion of stainless steel stresses the corrosion in the operating state of the device, while the conversion catalyst has more stringent requirements for chloride ions; poison doesn’t happen for the catalyst, so excessive chloride ions can be ruled out.
3.2 Manufacturing aspects of pipe fittings
In the investigation process, the manufacturer is required to submit quality certificates of the raw material, manufacturing process data of pipe fittings and quality certification documents (original records of the entire manufacturing process, intergranular corrosion test reports of raw materials and finished products, quality certification documents, etc.), original heat treatment records (all original heat treatment records and temperature curves). According to the information provided by the manufacturer, no problems have been found from the incoming inspection of the raw materials for pipe fittings to the quality control of the pipe fittings manufacturing process in compliance with the design standards.
3.3 Construction
Check the construction design manual of the hydrogen production unit and the welding procedure evaluation of the construction unit to confirm that the design does not require post-welding heat treatment. Considering that stainless steel is prone to chloride ion corrosion, the re-inspection report of the insulation material entering the factory was checked, and the manufacturer was required to provide an analysis report on the quality of cooling water used for washing after pickling. Chloride ions didn’t exceed the standard. At the same time, the project management department and the supervision company also re-examined all the on-site inspection and verification data of the hydrogen production plant construction, and no problems were found.
3.4 On-site detection of cracked pipe fittings
At the device site, inspectors were arranged to conduct a hardness test on a reducer of DN500*400 where cracks were found. The average value of the Brinell hardness (HB) was 146 and the highest value was 161. According to the standard of SH3408-96 "Steel Butt Welding Seamless Pipe Fittings", the hardness value (HB) of austenitic stainless steel pipe fittings should be less than and equal to 190, which meets the standard requirements. At the same time, the hardness test was carried out on the remaining stainless steel pipe fittings of DN200*150 in stock. The average Brinell hardness value was 140, and the highest value was 180, which met the standard requirements.
For the failed pipe fittings, a technical center was entrusted to conduct macroscopic, low-magnification analysis, chemical analysis, scanning electron microscope analysis, and metallographic analysis. The following conclusion came: the reducer is made from 0Cr18Ni10Ti austenitic stainless steel, and the metallographic structure is solid solution austenite. The reason for the cracking of the reducer is the result of corrosion fatigue damage.
3.5 Process medium and process operation investigation
Through the analysis of chlorine ions in the deoxygenated water, no chlorine ions were found in the analysis of various media, and there was no phenomenon of exceeding the standard; the investigation of the process operation records showed that the temperature and pressure in the operation were in line with the process indicators and design specifications. The influence of the process operation is therefore excluded.
4. Conclusion
In response to this leak, we organized a comprehensive and systematic investigation and related technical research in terms of pipeline design, pipe fitting manufacturing, pipeline installation, inspection and testing items of in-service pipe fittings, and production operation. It was concluded that 6 pipe fittings were caused by manufacturing issues and 1 pipe fitting was caused by corrosion fatigue.
5. Precautions
5.1 According to the investigation of other similar devices and the technical consultation with its design institute, it is considered that there is no problem in the selection of pipeline design materials. However, through the investigation of similar devices and the comparison of the piping design of the same process part with similar devices, it is found that there is a difference in the arrangement of the pipe support because there is no support at one end. This time, it has been redesigned by another design institute, confirmed and approved by the original design institute, and new pipe supports can be provided to the failed pipeline.
5.2 Conduct a comprehensive investigation of the supports of high-temperature hydrogen-prone pipe fittings, and rectify any problems found.
5.3 The process strengthens the smooth operation, reduces the impact of the medium on the pipeline, and prevents pipeline vibration.
5.4 Analyze the content of sulfur, chlorine and oxygen ions in the process medium once a week, and focus on monitoring the changes in these parameters.
5.5 Establish a pipe fitting ledger for the pipe fittings of the manufacturer; mark the model, location, process parameters and number, and list them as key parts for daily inspection, weekly inspection and post inspection. Realize timely discovery, timely processing, and timely elimination of hidden dangers.
5.6 During each maintenance period of the hydrogen production unit, all pipe fittings made by one manufacturer shall be listed as mandatory inspection items for non-destructive testing.
5.7 Make spare parts for the pipe fittings of the feeding line in the furnace area and other key parts for the next maintenance and replacement.
3.1 Design aspects
All stainless steel pipes and pipe fittings of this device are ordered according to the detailed engineering design "Comprehensive Material Lists" of the design institute, and the material is 0Cr18Ni10Ti. Conform to design specifications "Design and General Rules of Petrochemical Pipeline Layout" SH3012-2000, "Petrochemical Equipment and Design Specifications of Pipeline Thermal Insulation" SH3010-2000, "Design Specifications of Industrial Metal Pipelines" GB50316-2000. According to the design requirements, the pipe fittings are manufactured in accordance with the SH3408 "Steel Butt Welding Seamless Pipe Fittings" and the GB14976 Stainless Steel Seamless Pipes Conveying Fluid.
Relevant professional technicians of the design institute carefully analyzed and discussed the reducer of the pipeline of the hydrogen production unit, and conclude that the pipeline is made from stainless steel SS321, which will not cause hydrogen corrosion according to the working temperature and working pressure, and conforms to the material selection requirements of "General Rules for Selection of Petrochemical Pipeline Design Equipment". The maximum working temperature of the pipeline is 420°C and the maximum working pressure is 3.5MPa, and according to the calculation formula in the "General Rules for Selection of Equipment for Petrochemical Pipeline Design”, DN300 is obtained after considering the negative deviation and the maximum inner wall thickness is only 7.85mm. According to the design wall thickness of SH3405, SCH40s is selected for the design wall thickness; the maximum inner wall thickness of the elbow after considering the negative deviation of DN400 is only 9.6mm, and the design wall thickness is 13mm; the maximum inner wall thickness of the elbow after considering the negative deviation of DN500 is only 14.2mm, and the design wall thickness is 15mm. There is no problem in the design of wall thickness; the water injection position is based on the equipment drawings and technology provided by the desuperheater manufacturer. There is no problem. Chloride ions should be mainly considered for the corrosion of stainless steel stresses the corrosion in the operating state of the device, while the conversion catalyst has more stringent requirements for chloride ions; poison doesn’t happen for the catalyst, so excessive chloride ions can be ruled out.
3.2 Manufacturing aspects of pipe fittings
In the investigation process, the manufacturer is required to submit quality certificates of the raw material, manufacturing process data of pipe fittings and quality certification documents (original records of the entire manufacturing process, intergranular corrosion test reports of raw materials and finished products, quality certification documents, etc.), original heat treatment records (all original heat treatment records and temperature curves). According to the information provided by the manufacturer, no problems have been found from the incoming inspection of the raw materials for pipe fittings to the quality control of the pipe fittings manufacturing process in compliance with the design standards.
3.3 Construction
Check the construction design manual of the hydrogen production unit and the welding procedure evaluation of the construction unit to confirm that the design does not require post-welding heat treatment. Considering that stainless steel is prone to chloride ion corrosion, the re-inspection report of the insulation material entering the factory was checked, and the manufacturer was required to provide an analysis report on the quality of cooling water used for washing after pickling. Chloride ions didn’t exceed the standard. At the same time, the project management department and the supervision company also re-examined all the on-site inspection and verification data of the hydrogen production plant construction, and no problems were found.
3.4 On-site detection of cracked pipe fittings
At the device site, inspectors were arranged to conduct a hardness test on a reducer of DN500*400 where cracks were found. The average value of the Brinell hardness (HB) was 146 and the highest value was 161. According to the standard of SH3408-96 "Steel Butt Welding Seamless Pipe Fittings", the hardness value (HB) of austenitic stainless steel pipe fittings should be less than and equal to 190, which meets the standard requirements. At the same time, the hardness test was carried out on the remaining stainless steel pipe fittings of DN200*150 in stock. The average Brinell hardness value was 140, and the highest value was 180, which met the standard requirements.
For the failed pipe fittings, a technical center was entrusted to conduct macroscopic, low-magnification analysis, chemical analysis, scanning electron microscope analysis, and metallographic analysis. The following conclusion came: the reducer is made from 0Cr18Ni10Ti austenitic stainless steel, and the metallographic structure is solid solution austenite. The reason for the cracking of the reducer is the result of corrosion fatigue damage.
3.5 Process medium and process operation investigation
Through the analysis of chlorine ions in the deoxygenated water, no chlorine ions were found in the analysis of various media, and there was no phenomenon of exceeding the standard; the investigation of the process operation records showed that the temperature and pressure in the operation were in line with the process indicators and design specifications. The influence of the process operation is therefore excluded.
4. Conclusion
In response to this leak, we organized a comprehensive and systematic investigation and related technical research in terms of pipeline design, pipe fitting manufacturing, pipeline installation, inspection and testing items of in-service pipe fittings, and production operation. It was concluded that 6 pipe fittings were caused by manufacturing issues and 1 pipe fitting was caused by corrosion fatigue.
5. Precautions
5.1 According to the investigation of other similar devices and the technical consultation with its design institute, it is considered that there is no problem in the selection of pipeline design materials. However, through the investigation of similar devices and the comparison of the piping design of the same process part with similar devices, it is found that there is a difference in the arrangement of the pipe support because there is no support at one end. This time, it has been redesigned by another design institute, confirmed and approved by the original design institute, and new pipe supports can be provided to the failed pipeline.
5.2 Conduct a comprehensive investigation of the supports of high-temperature hydrogen-prone pipe fittings, and rectify any problems found.
5.3 The process strengthens the smooth operation, reduces the impact of the medium on the pipeline, and prevents pipeline vibration.
5.4 Analyze the content of sulfur, chlorine and oxygen ions in the process medium once a week, and focus on monitoring the changes in these parameters.
5.5 Establish a pipe fitting ledger for the pipe fittings of the manufacturer; mark the model, location, process parameters and number, and list them as key parts for daily inspection, weekly inspection and post inspection. Realize timely discovery, timely processing, and timely elimination of hidden dangers.
5.6 During each maintenance period of the hydrogen production unit, all pipe fittings made by one manufacturer shall be listed as mandatory inspection items for non-destructive testing.
5.7 Make spare parts for the pipe fittings of the feeding line in the furnace area and other key parts for the next maintenance and replacement.
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