Manufacturing Processes of High-temperature & High-pressure Hydrogen Valves

Manufacturing Processes of High-temperature & High-pressure Hydrogen Valves


The high-temperature and high-pressure hydrogenation valve is an important pipeline component of the hydrogenation system in the petrochemical industry. The pressure level is above ANSI CL900, and the medium temperature is 0 to 500°C. The material of the valve body is forged and cast carbon steel (CS), Alloy steel and stainless steel. The types of valves include conventional shut-off valves such as gate valves, globe valves, check valves and ball valves. The medium for storage and transportation of high-pressure hydrogen valves (including pipelines) is flammable and explosive high-pressure gas (hydrogen or oil gas plus hydrogen). If the valve is damaged, it will cause a serious accident. Therefore, strict requirements are put forward on the material, structural design, strength design and manufacturing quality of the valve.
 
Materials for pressure-bearing shells
When carbon steel is used for pressure-bearing castings such as valve bodies and bonnets (including forging blanks), electric arc furnaces or other smelting processes should be used, and castings should be normalized. When austenitic stainless steel is used for pressure castings such as valve bodies and valve bonnets, intermediate frequency furnace plus AOD argon oxygen refining furnace or other smelting methods should be used, and the contents of harmful impurity elements such as S and P should be less than 0.02% and 0.03%. Austenitic stainless steel castings should be solution treated.
 
Inspection
(1) General rules
Each batch of castings and forgings (referring to the same batch number, same material, same specification, same furnace number, and same heat treatment conditions) shall be subject to a random inspection of chemical composition and mechanical properties at least once, and the test results shall meet the requirements for API, ASME, ASTM, MSS and other corresponding standards. Each batch of castings and forgings shall be randomly inspected for metallographic structure and corrosion test at least once, and the test shall be carried out according to ASTM E381 standards. The grain size of carbon steel should not be lower than the requirements of grade 5 in ASTM E112 standard, and that of stainless steel should not be lower than grade 7 in ASTM E112 standard. Castings and forgings should be free of dendrites and columnar structures, and non-metallic inclusions should not be lower than the ASTM E45 standard. Sulfide is less than and equal to grade 1.5, silicate grade 2.5, alumina grade 2.5 and spheroidized oxides grade 3. The total grades should be grade 6. 5. Segregation and banded heterogeneous structures with a size larger than grades 2.5 in the ASTM E45 standard are not allowed, and strip slag inclusions and cracks are not allowed.
 
(2) Appearance
The visual inspection of castings should be carried out one by one, and the product quality should meet the requirements for Grade B in the MSS SP-55 standard. For scars, cracks, folds and slag inclusions whose depth is not greater than 10% of the designed wall thickness and which do not get into the minimum wall thickness, cracking, folding and slags; grinding can be used. The remaining wall thickness after eliminating defects should not be less than the minimum wall thickness. Otherwise, the casting should be scrapped. Microcracks whose depth is not greater than 0.8mm, it is allowed to grind and remove them. If the depth of microcracks is greater than 0.8mm, the casting will be scrapped. The valves with casting pressure above 600 lb should be inspected one by one. The scope of the inspection is in accordance with ASME B16.34. Inspection results and inspection methods shall be carried out according to MSS SP-54 standard; porosity (A) shall not be less than Grade 2, and slag inclusions (B) shall not be less than Grade 2 grades. Shrinkage cavities (CA, CB, CC and CD) shall not be less than Grade 2. There should be no heat cracks and cold cracks. The pressure-bearing forged parts shall be ultrasonically inspected one by one, and the inspection shall be carried out in accordance with the ASTM A388 standard. The size of a single defect in a forging should not be larger than the equivalent diameter of 4mm, and the equivalent diameter of 3mm in the range of 50cm2 for dense defects should not exceed 5 echoes.
 
(3) Non-destructive testing
For carbon steel castings and forgings, magnetic particle inspection shall be carried out one by one, and the inspection shall be carried out by the ASTM E709 standard. As a result, there should be no hot and cold cracks; the length of any linear display should not be greater than 2mm, and the size of a single circular defect should not be greater than 4mm; the cumulative length of defects in any area of 100mm × 100mm should not exceed 2mm. For stainless steel castings and forgings, liquid inspection shall be carried out one by one, and the inspection shall be carried out in accordance with ASTM A165 standards. As a result, there should be no hot cracks and cold cracks, and the length of any linear display should not exceed 2mm. The size of a single circular defect should not exceed 4mm, and the cumulative length of defects should not exceed 2mm in any area of 100mm × 100mm. Only grinding is allowed to remove the defect, and repair welding is not allowed.
 
(4) Others
For austenitic stainless steel forgings or castings, the intergranular corrosion test shall be randomly inspected for each batch, and the test method and test results shall meet the requirements of ASTM E262 E. Austenitic stainless steel castings or die forgings should be pickled and passivated. The materials of each part of the valve shall comply with the NACE MR0175 standard to ensure that the materials of each part meet the use under the condition of hydrogen sulfide.
 
Machining
During mechanical processing, the corresponding inspection and control shall be carried out according to the shutdown waiting points and on-site witness points set up in the prepared manufacturing quality plan. Designate special processing equipment (CNC machine tools) and operators for important parts to ensure that the size and accuracy of the processed parts meet the requirements of the drawings, and mark traceability marks on the parts. The processing of special parts adopts special tooling or auxiliary devices to ensure that the size and accuracy of the processed parts meet the requirements.
 
Special processes
For special processes such as welding (including surfacing), heat treatment, and non-destructive testing, process tests and process evaluations shall be carried out by corresponding standards. According to the results of process tests and process evaluation, prepare process regulations or process cards to guide production. Operators engaged in special procedures such as welding (including surfacing), heat treatment and non-destructive testing shall conduct skill assessment in accordance with the corresponding standard requirements, obtain corresponding qualification certificates, and conduct actual operations according to the allowable operating range of the qualification certificate.
 
Testing valves 
Check the valve machine according to the drawings and the corresponding standard requirements. After passing the product’s test inspection program or the corresponding standard requirements, the valve is tested for hydraulic strength, sealing, upper sealing and air sealing; the valve is closed manually or electrically and travel limit and other functional tests are performed. All tests should meet the requirements before leaving the factory. For valves with special requirements, a bench loop test of simulated working conditions can be supplemented to further assess other performance indicators. After passing the inspection and test, the valve shall be cleaned, dried or painted on the surface according to the corresponding standard requirements.
 
Packaging
Valve packaging is carried out by the technical agreement or user requirements, and corresponding inspection reports, test reports, valve drawings, quality records, operation and maintenance manuals, product qualification certificates and other materials are provided following the technical agreement or user requirements.
 
Conclusion
The medium of hydrogen and hydrogen sulfide has very strict requirements on the materials of storage and transportation equipment. Therefore, in the production and manufacture of high-temperature and high-pressure hydrogen valves, quality control procedures should be strictly followed.