General Provisions:

The plate-type flat-welded flange is designed in accordance with relevant standards and the user’s technical requirements, taking into account our company’s specific manufacturing and testing equipment.

1. Materials

1.1 Material Selection

a. The flanges shall be made from forged blanks or plates that meet the mechanical performance and chemical composition requirements specified in the relevant standards for the parent pipe material.

b. Carbon Equivalent (Ceq): The carbon equivalent value of the material should be appropriate. A carbon equivalent that is too high can adversely affect the material’s weldability, while a carbon equivalent that is too low can compromise the hardenability of the steel pipe when heated, resulting in a low strength of the quenched microstructure.

c. The surface of the selected materials shall be free from oil, excessive rust, flux residues and corrosive substances, low-melting-point metal contamination, and obvious dents or defects on the pipe surface. Pay special attention to the surface condition at weld repair areas and the dimensions of pipe ends.

d. The material markings are clear and complete, and meet the technical requirements specified in the relevant standards.

1.2 Selection of Materials

The selection of billet materials for flanges should be based on the actual conditions after flange forming and the forging ratio, choosing billets of different specifications. The billet calculations shall be performed according to the principle of constant weight, and process cards shall be issued accordingly.

1.3 Inspection of Materials

a. Before incoming inspection, use a wire brush and an angle grinder to mechanically remove rust from the material surfaces.

b. After rust removal, perform surface and dimensional inspections on the materials.

c. Materials shall undergo material analysis or spectral analysis by furnace number to determine elemental content and perform performance testing.

1.4 The material’s traceability markings shall be clearly identifiable. During the manufacturing process, records must be kept to ensure traceability of material transfers, including the furnace number, batch number, length of the raw materials, the material number after the material has been coiled into straight-seam pipes, the length of the materials used, and the specific locations where these materials were utilized.

2. Product Processing Procedure

2.1 For materials according to user-specified dimensions, cold cutting using a gantry band saw is the most suitable method for cutting stainless steel materials. Hot cutting methods such as plasma cutting should be avoided to minimize material waste and prevent microstructural changes in the fracture surface or heat-affected zone. This also helps to avoid defects such as quenched layers or cracks caused by improper handling during the cutting process. After cutting, use a grinding wheel to smooth the cut ends, removing burrs and sharp edges. For carbon steel materials, oxygen-acetylene flame cutting or band sawing is recommended. During the cutting process, it is essential to mark and transfer necessary identification labels based on the material’s specifications and composition, and each finished blank must undergo individual inspection of its geometric dimensions.

2.2 Forging of Flange Billets: Flanges are forged by heating qualified billets in a heating furnace according to the forging process requirements for the corresponding materials. For large-sized pipe fittings, the billets must be freely forged under a split hammer. All flange billets must meet or exceed the requirements for Class II forgings. Billets made of different materials shall be processed according to the specified process sheets that outline the appropriate heating temperatures and holding times.

2.3 Heat Treatment of Pipe Fitting Blanks (Flange Blanks): The heat treatment of pipe fittings that have undergone hot (or cold) forming and forged flange blanks is carried out according to the heat treatment processes specific to different materials, in order to eliminate residual stresses, refine the microstructure, and enhance the material’s overall performance, including strength and toughness. The heat treatment process shall be executed in accordance with the heat treatment process card. The steps of the heat treatment shall comply with the following requirements:

2.3.1 Inspect all components of the heat treatment furnace: burners, thermometers, fans, oil pump systems, trolley mechanisms, furnace door lifting devices, etc., should be in normal standby condition, and the fuel level in the oil storage area should be sufficient to meet the requirements of heat treatment operations.

2.3.2 Furnace Loading: (1) Workpieces should be elevated by approximately 400 mm. They should be arranged in such a way that they do not exert pressure on each other, with a spacing of 150 mm to prevent deformation and ensure uniform cooling and heat dissipation. Arrange the workpieces reasonably according to their shapes, draw a rough sketch showing the dimensions of the arrangement, and assign numbers to each piece while keeping detailed records. (2) Flanges should be placed flat on the trolley to prevent bending and deformation after heating. (3) Adjust the fire-retardant walls so that the flame does not directly impinge on the workpieces.

2.3.3 Before ignition, check whether the furnace sand seal is in good condition. If there are any gaps, seal them using fireclay or high-temperature aluminum silicate asbestos.

2.3.4 When firing a heat treatment furnace that is initially cold, it is advisable to use half of the burners (i.e., light every other burner). If the furnace is being fired from a warm state, all burners can be lit at once. Note that the heating rate, holding time, cooling method, and other parameters must comply with the specified heat treatment process.

2.3.5 Adjust the damper of the flue and the oil nozzle’s oil and air flow rates to ensure uniform temperature in the heat treatment furnace and balanced readings from all thermocouples. Operators shall record the furnace temperature every 15 minutes.

2.3.6 Operators should regularly patrol and inspect the operation of the oil furnace, using the observation port to monitor the combustion condition inside the furnace chamber. If combustion is poor, promptly adjust the air and oil flow rates at the burner nozzles. If any doubt arises regarding the furnace temperature indication, use an optical pyrometer for comparison and identify the root cause before taking corrective action.

2.3.7 Before the workpiece is removed from the furnace, close all oil nozzles and dampers, and complete the “Heat Treatment Process Parameter Record.”

2.3.8 Normalizing and tempering heat treatments can be carried out in two separate steps. If these steps are performed continuously in one go, the bending pipe must be cooled to below 300℃ after normalizing before tempering can begin.

2.3.9 The same furnace must be loaded only with flanges made of the same material or of corresponding specifications.

2.3.10 Phase inspection shall involve no fewer than one specimen per furnace; hardness inspection shall involve no fewer than two specimens per furnace, with each specimen tested at no fewer than three points. The testing locations shall be the base metal on the tensile side and the area of maximum deformation.

2.4 Machining and Forming: According to the specifications and model requirements of various pipe fittings, the raw materials are machined and formed using machinery such as lathes and drilling machines in compliance with applicable standards, ensuring that the finished pipe fittings meet the standard requirements for appearance and geometric dimensions. The inspection department conducts tests on the products in accordance with the standard requirements for geometric dimensions and geometric tolerances. After machining, stainless steel pipe fittings undergo pickling and passivation treatment; if necessary, intergranular corrosion testing shall also be performed.

3. Inspection and testing (type tests are not performed by our company)

3.1 Surface Quality

3.1.1 The flange surface shall be free of cracks, overburning, overheating, and other defects; the surface should also be free of hard spots.

3.1.2 The inner and outer surfaces of the flange shall be smooth and free from defects that could impair strength or appearance, such as knots, scratches, and laps. Any defects detected during inspection shall be ground down and removed. The ground areas shall be smoothed until dye penetrant or magnetic particle testing confirms that the defects have been completely eliminated. The thickness of the flange after grinding shall meet the specified requirements.

3.1.3 Pits with a depth exceeding 3.15 mm on flange end bodies and pits with a depth exceeding 1.5 mm on weld seams shall not be repaired by hammering.

3.1.4 Repair of Defects

Sharp notches and scratches on the pipe body with depths less than 5% of the nominal wall thickness shall be smoothly ground and smoothed.

Isolated round-bottom marks do not need to be ground.

3.1.5 Any cracks, overburning, overheating, or hard spots on the flange are not permitted; defects in the flange body are not allowed to be repaired by welding.

3.2 Geometric dimension inspection shall be conducted in accordance with the corresponding standard dimensional requirements.

3.3. Nondestructive Testing of Hot-Pressed Flanges

3.3.1 Nondestructive testing of flanges shall be performed after the flanges have undergone heat treatment. Commonly used nondestructive testing methods include magnetic particle inspection, ultrasonic testing, radiographic testing, and dye penetrant testing, and specific operating procedures for nondestructive testing must be established.

3.3.2 Equipment used for magnetic particle inspection shall generate a magnetic field perpendicular to the weld seam in the transverse direction, with a strength sufficient to reveal open welds, partial fusion or incomplete fusion, weld discontinuities, cracks, fissures, and slag inclusions on the surface of the steel pipe.

3.3.3 The depth of all defects detected by magnetic particle inspection shall be measured. When the indicated depth exceeds 5% of the specified wall thickness, the defect must be ground down.

3.3.4. When performing shear-wave testing using ultrasonic inspection, the sensitivity of the testing equipment shall be calibrated using a reference standard. The reference standard shall have the same manufacturing process, material, and specifications as the test piece. On the reference standard, vertically through-holes with a diameter of 1.6 mm shall be drilled along the direction perpendicular to the wall thickness. If the signal generated by a defect is equal to or greater than 100% of the echo amplitude produced by the 1.6-mm-diameter through-hole in the reference standard, the defect must be ground down. If the defect detected is a delamination defect, longitudinal-wave testing may be used instead. The sensitivity of the longitudinal-wave testing shall be calibrated using a reference standard that has the same manufacturing process, material, and specifications as the test piece; on this reference standard, a flat-bottomed hole with a diameter of Φ6 shall be drilled, with the depth of the flat-bottomed hole being half the wall thickness of the test piece. Testing shall then be carried out accordingly.