1 Products Description
The original oxidation reactor of a PIA (refined isophthalic acid) unit was revamped due to the change of production process. The design scale of the revamped PIA was 50000 t/a. The oxidation reactor, the core equipment in the unit, has been in operation for about 30 years before the transformation, and will be used as the first crystallizer after the transformation. The design temperature of the original oxidation reactor is 300 ℃, the working temperature is 189 ℃ ± 4 ℃, the design pressure is 3.5MPa, and the working pressure is 1.05~1.25MPa. The design temperature of the first crystallizer after transformation is 215 ℃, and the working temperature is 177 ℃; The design pressure is 1.65MPa and the working pressure is 0.7MPa. Its service pressure and service temperature are reduced. The equipment is a titanium clad steel plate for chemical industry, with a height of 9004mm, an inner diameter of 2825mm, and a wall thickness of 29mm+2.1mm. The main content of the equipment transformation is to cut off the internal extension of the original two connecting pipes and add two new connecting pipes. The total mass of the transformation part is 150kg. The new nozzle is used as the import and export of main materials respectively.
2 Characteristics and construction protection of titanium steel composite plate
2.1 Titanium-steel composite plate
The composite method of titanium clad steel plate for chemical industry is explosive method. The base layer of the new nozzle and flange is separated from the lining layer, only to achieve a close fit. The base material of the equipment barrel and the newly added nozzle flange is Q345R, and the barrel cladding and nozzle lining material is GR3 (in accordance with the requirements of ASME SB265Gr2). The physical properties and welding properties of Q345R and GR3 differ greatly.
2.2 Industrial pure titanium is a silver white metal with a density of 4.51g/cm3, equivalent to 57% of steel. Titanium has poor conductivity, low thermal conductivity and linear expansion coefficient (thermal conductivity is 1/4 of iron, non-magnetic. Titanium has the advantages of both steel (high strength) and aluminum (light texture). Industrial pure titanium has good plasticity, yield strength is close to tensile strength, and can maintain relatively high specific strength at high temperature. Titanium is a very active metal with high affinity with oxygen. It forms a dense, adhesive and inert oxide film on the surface of the oxygen-containing medium. Even if it is subject to mechanical wear, it will regenerate quickly to protect the titanium matrix from corrosion.
3Construction protection
According to the analysis of the characteristics of industrial pure titanium, necessary protection should be done during the equipment transformation process, including: laying rubber plates for the equipment manhole to prevent damage to the manhole connecting pipe and the normal surface; Steel scaffold shall not be erected inside the equipment to avoid titanium surface damage or iron ion pollution; The lower part of the equipment opening shall be paved with rubber sheet, and the upper layer of the rubber sheet shall be paved with fireproof cloth to prevent the titanium clad layer from being damaged during construction and from being polluted by cutting and welding spatter. The source of iron pollution must be removed during the preparation and welding process before welding. The pre-weldment must not be cleaned with wire brush or abrasive paper, and special stainless steel or non-ferrous metal processing tools must be used.
4 Wall plate opening
The surrounding titanium cladding shall be protected from damage during the opening process of the wall panel. The titanium clad layer is mechanically perforated and stripped from the base layer. The base Q345R metal is processed by flame cutting and grinding wheel. First, position and mark the new nozzle. See Fig. 1 for each machining dimension.
4.1 Step 1: Cut the hole from the titanium clad side with cobalt and grinding wheel, and peel the titanium clad at the opening position with a steel chisel.
4.2 Step 2 Use flame cutting method to open holes and groove the base metal, and pay attention to protect the titanium cladding from damage or discoloration when cutting.
4.3 Step 3 Remove the size allowance (3mm thick) reserved for thermal cutting of base metal by grinding wheel until it reaches the opening size required by the design drawing, and process the groove to expose the metal luster.
4.4 Step 4 Grind and repair the opening edge of titanium clad layer. After the hole is processed at the opening position required by the drawing, the processed clad layer shall be subject to penetrant testing and 100% ultrasonic testing in two directions at right angles with the same probe to ensure no separation and subsurface defects.
5 Assembly of titanium lining layer
After the welded joint of base metal is qualified and polished, the titanium lining layer shall be assembled. The assembly is carried out in three steps: Step 1, put the titanium backing rings 1 and 2 into the stripping position (see Figure 2), the width of the backing ring is 30mm, the thickness is 3mm, and the gap between the two sides of the backing ring is 1mm. Step 2, insert the loose liner of the titanium flange into the base flange mouth, and the liner is required to fit closely with the base steel components; Step 3: Assemble the sealing surface of titanium flange, which should be fitted with the base flange surface.
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