How to inspection of tube sheet and baffle

1. Inspect tubesheet hole

Check the arrangement of tube sheet holes, hole center distance, tube sheet hole diameter and allowable deviation according to the drawing requirements. The heat exchanger purchased by our company generally adopts seamless steel tubes for petroleum cracking (GB 9948). The drawing is designed as grade I tube bundle. The center distance, diameter and allowable deviation of tubesheet hole shall meet the requirements of design drawings, and shall not be lower than the specification of tubesheet hole diameter and allowable deviation of class I tube bundle (applicable to carbon steel, low alloy steel and stainless steel heat exchange tube) in GB 151 shell and tube heat exchanger. For the tube sheet of heat exchanger made of copper nickel alloy and other materials, we think that the hole diameter and allowable deviation of tube sheet should be more strict than that of grade I tube bundle in GB 151 standard, so as to prevent over expansion when the structure of strength expansion + seal welding is adopted for the connection of heat exchanger tube and tube sheet. Or in the design, it is not necessary to mark it as grade I tube bundle according to the provisions of GB 151 for the diameter and allowable deviation of tube sheet hole of copper and copper alloy heat exchange tube. During the inspection, spot check shall be carried out for the pipe holes in the area with the center angle of the pipe plate not less than 60 °. In this area, 4% of the deviation on the pipe holes is allowed to be 0.15mm larger than the value specified in GB 151, but not more than 5.

2. Inspect tube Sheet

If the tube plate is spliced, the butt weld of splicing shall be subject to 100% ray or ultrasonic flaw detection, the qualification standard is JB 4730, the ray is not lower than level II, and the ultrasonic is not lower than level I. After splicing, the tube sheet shall be subject to stress relief heat treatment (except for stainless steel). The composite tube sheet shall be selected according to the design drawings and national standards. The composite sheet shall be supplied after heat treatment, and 100% ultrasonic testing shall be carried out to ensure that the two materials are well compounded. The qualification standard is JB 4730 class I. The thickness of the composite layer indicated in the drawing shall be the thickness of the tube sheet after processing.

3. Inspect width deviation of tube plate hole bridge

In the inspection, spot check shall be carried out on the surface (back) of the final (exit) drilling side to ensure that the width of the hole bridge is not less than 60 ° in the center angle area of the tube sheet. The qualified standard is the requirement marked on the design drawing, and shall not be lower than the width of steel grade I tube bundle bridge specified in GB 151. The qualified rate shall not be less than 96%, and the minimum width of tube plate hole bridge shall be controlled within 4% and no more than 5 places. If the qualified rate is exceeded, the whole tube plate shall be inspected.

The tube sheet hole shall be strictly perpendicular to the tube sheet sealing surface, with an allowance of 0.05m m, and there shall be no through longitudinal or spiral striations on the tube sheet hole surface. The surface roughness Ra of the tube sheet hole shall not be greater than 12.5 μ m (when the heat exchange tube and tube sheet are expanded or strength expanded + sealed welding), and the pull off groove shall be inspected according to the drawing requirements; the sealing surface and other geometric dimensions of the tube sheet shall be in accordance with the drawing requirements.

For the heat exchanger, the processing accuracy of tube sheet is the key to the connection and assembly of tube bundle between tube sheet and tube sheet. The deviation of the hole center distance of tube sheet directly affects the construction quality of welded pipe and expanded pipe. The main reason to limit the width deviation of the back hole bridge is to consider the influence of the thickness of the tube sheet on the drilling. The high perpendicularity and finish of the tube sheet hole can prevent the damage of the heat exchange tube during the installation of the tube and ensure the quality of the expansion joint. At present, domestic manufacturers use CNC drilling machine in the mechanical manufacturing industry. According to the arrangement of tube sheet holes and the hole diameter and hole center distance, 24 tube sheet holes or 36 tube sheet holes are drilled at a time, with relatively high processing accuracy. However, in the chemical machinery manufacturing industry, the use of CNC drilling machine is rarely seen, and there is still a great space for improving the processing accuracy and quality of tube sheet holes.

4. Inspect baffles

According to the requirements of the design drawing, the diameter and allowable deviation of the orifices of the baffles shall meet the requirements of the drawings, and shall not be lower than the diameter and allowable deviation of the orifices of the first level tube bundle baffles and supporting plates in GB 151; in addition to meeting the requirements of the drawings, the copper nickel alloy baffles shall meet the requirements of the drawings, It shall also not be lower than the provisions of GB 151 on the diameter and allowable deviation of the orifices of baffles and supporting plates of copper and copper alloy heat exchange tubes, and shall not be in accordance with the provisions on the diameter and allowable deviation of orifices of baffles of class I tube bundles. The allowable number of pipe holes exceeding 0.1mm shall not exceed 4% of the inspection range, and shall not exceed 5. The surface roughness Ra of the baffle outer circle shall not be greater than 25 μ m, and the sharp angles on both sides of the outer circle surface shall be blunt. Remove any burr on the baffle plate. The two ends of the baffle plate hole of the copper nickel alloy heat exchange tube shall also be chamfered by 30 °× 1mm to prevent scratching the heat exchange tube.

For tubesheet and baffles, processing defects are easy to be found in the intermediate inspection, mainly including composite tubesheet, the composite layer does not have enough machining allowance, the composite layer becomes thinner after processing, or the geometric dimension of the sealing surface of tubesheet is changed to ensure the thickness of composite layer, resulting in installation difficulties; when drilling tubesheet holes, the drill bit is replaced midway, so that the tubesheet hole diameter and tolerance exceed the standard, and the heat exchange tube is over expanded when expanding the tube, The service life of heat exchanger is affected; both ends of tube sheet hole and baffle tube hole are not chamfered and deburred according to the requirements of the drawing, and the heat exchanger tube is scratched when assembling the tube bundle, while the tube hole on the tube sheet is not chamfered or fails to meet the requirements of the drawing chamfering, so that the strength welding becomes sealed welding, and sealed welding becomes surface sticking welding. The existence of these defects will shorten the service life of the heat exchanger.

Tube Sheet