Material requirements for heads made of dual-phase steel clad plates

  The head is one of the important pressure components of the pressure vessel. It not only directly affects the manufacturing quality and cost of the vessel, but also affects the production, the safe and long-term operation of the production equipment, therefore, it is extremely important to adopt a reasonable manufacturing process of the head. There are many ways to form the head, common ones are cold stamping, hot stamping, cold spinning, hot spinning, etc. of the whole plate or jointed plate, and the heads can also be tailor-welded after split forming. The forming of composite material heads can generally be cold stamped, medium temperature forming, hot forming, and split and pressed before tailor welding, etc., mainly based on the specifications of the head, material characteristics, equipment production capacity, and required performance indicators. determine. Duplex stainless steel has a ferrite phase and austenite phase each accounting for about 50% in its solid solution structure. Generally, the content of less phases needs to be at least 30%, because this material has the excellent toughness and toughness of austenitic stainless steel. Weldability, as well as the higher strength and corrosion resistance of ferritic stainless steel, has become more and more widely used in petrochemical equipment, seawater and sewage treatment equipment, papermaking machinery and other industrial fields in recent years. In this paper, combined with the manufacturing of the duplex stainless steel heat exchanger composite plate head contracted by a company, the forming process and material requirements of the duplex stainless steel composite plate material head are systematically explained. After the head is formed, its appearance and size are systematically explained, Non-destructive testing is carried out, and all the indicators meet the required values in the head manufacturing standards; physical and chemical performance tests are carried out on the test plates with the furnace to verify that the performance indicators of the head plate materials in the forming process meet the material standards The range of values required in, determines the feasibility of the molding process.

  1 Overview of the head and material requirements

  Standard oval head, thickness (19+3)mm, design material is SA-516.Gr485+UNSS31803, material conforms to ASMECodeSectionⅡand SectionⅧDiv.1; strength calculation is calculated based on the thickness of the base layer, and the coating is only used for corrosion allowance , The medium in contact with it is highly corrosive, and the equipment has been operating under high temperature and high pressure for a long time, so there are many requirements for materials in the design. The composite board manufacturing process uses explosive compounding. After compounding, the structure, mechanical properties, and corrosion resistance of the base material and cladding material may change, and some performance indicators of the raw materials will also change, which is very likely to reduce the use of equipment. Life span affects the safe production of the entire device. Therefore, when purchasing head plate materials, strict requirements must be put forward for base materials, cladding materials and composite panels to ensure quality.

  Base material requirements

  The base material procurement requirements meet the requirements of ASMESA-516Gr485 (2013 edition), and the delivery state of the steel plate is normalized and the thickness is 20mm. 100% UT inspection on the surface of the steel plate, the acceptance standard is in accordance with SA-578/SA-578M (2013 edition), C level. The impact test requirements and methods are in accordance with the standard SA-370/SA-370M (2013 edition), and the test temperature is 0°C. Re-inspect the plates when they are accepted. Through re-inspection, it is concluded that all performance indicators of the base material meet the required values specified in the standard.

  Cladding material requirements

  The cladding material procurement requirements meet the requirements of ASMESA-240M, UNSS31803 (2013 edition). The delivery state of the steel plate is solid solution treatment, and the thickness is 4mm. The intergranular corrosion test is in accordance with the C method of ASTM A923-03 standard. The metallographic inspection is carried out in accordance with ASTM A293-01, GB/T13305-2008 "Metallographic Determination of α-Phase Area Content in Stainless Steel". Re-inspect the plates when they are accepted. After the sample was corroded in a 40% sulfuric acid + iron sulfate solution, there was no crack and no intergranular corrosion after being bent 180°. The metallographic structure of the sample after corrosion by ferric chloride hydrochloric acid aqueous solution is mainly austenite and ferrite, and the ferrite content is about 50%.

  Composite board requirements

  The composite board adopts the explosive welding manufacturing process, and the composite board is required to meet the requirements of ASMESA-264 (2013 edition). The composite plate will produce welding residual stress during the explosive compounding process. In addition, the mechanical properties and corrosion resistance of the base material and the cladding material will change after the explosive welding. Therefore, after the explosive welding, post-weld heat treatment and solution treatment are generally required to eliminate Residual stress generated by explosive welding to ensure the mechanical properties and corrosion resistance of the composite board. The delivery heat treatment temperature of S31803 composite steel plate is 970±10℃, and the heat preservation is 0.5h. Measure the thickness after explosive compounding, the minimum thickness is not less than (18+3)mm, and the surface unevenness of the whole board is ≤1mm/1m. The lamination quality is 100% UT inspection according to SA-578/SA-579M (2013 edition) and its additional requirements. The qualified grade is SA-264, Class 1. The lamination part is subjected to shear test, and the shear strength is required to be ≥210MPa. The base material requires impact test and grain size inspection, and the cladding material is calculated based on the strength only as a corrosion allowance, not required

  Included in the tensile test, so the test value is for reference only. The cladding material requires a bending test, one of which is in a tensile state and the other is in a compressed state to determine the ductility of the material. And the coating material requires ferrite metallographic inspection and intergranular corrosion test. When the steel plate is accepted, the minimum coating thickness measured is 3.72mm, the flatness is about 0.8mm/1m, and the 100% UT inspection of the bonding part is qualified. Re-inspection of the plates is performed during acceptance. The standard values and re-inspection values of mechanical properties are shown in Table 5. The strength of the two shear specimens is 310 and 316 MPa, which are both greater than the standard required value of 210 MPa. The impact absorption energy of the base layer is respectively 160, 140, 148J, which are all greater than the average value of 24J required by the standard. After observation, no second phase precipitation or segregation phase was found at the grain boundary. The area percentage of the α-phase of the duplex stainless steel sample was about 45%. According to the metal average grain size measurement method, the grain size is set to 10 levels. Coated samples were tested for intergranular corrosion in accordance with ASTM A923-03 (Method C). After the samples were corroded and bent, cracks and intergranular corrosion did not occur.

Material requirements for heads made of dual-phase steel clad plates
- 29 Nov 2019 -
english china rus esp