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Welding technology requirements for titanium heat exchangers in petrochemical industry

Because the titanium tube heat exchanger has high corrosion resistance, yield strength and density ratio, small thermal expansion coefficient, long service life, high heat transfer efficiency, not easy to scale advantages can greatly improve the service life of titanium heat exchanger, reduce the loss caused by corrosion failure shutdown, good economic benefit, is widely used in petrochemical and other fields.

For the titanium tube condenser of PTA plant ordered by yangzpetrochemical, the design pressure is 0.6mpa in the shell range, 3.1mpa in the pipe range, and the design temperature is 80°C in the shell range and 210°C in the pipe range. The medium in the shell range is circulating water, and the medium in the pipe range is TA, water, HAC, ionic bromide and inert gas.The manufacturing conditions require that the order be mock-up tested prior to commencement of the order, that is, the welder and welder operator are assessed according to the rated WPS, and each welder participating in the welding is assessed to determine the welder or welder operator's ability to produce quality welds.The procedure for the module test is in accordance with ASME boiler and pressure vessel code part ix: welding and brazing conformity assessment, chapter iii welding skill assessment requirements, which shall be witnessed and inspected by the owner or the project management team.

The connection form of heat exchange tube and tube plate is as follows: light expansion pair medium + strength welding + sticking expansion; the end of heat exchange tube sticks out from the tube plate surface 0.5-1.0mm; welding of tube mouth adopts manual tungsten-argon arc welding and two-pass welding, and the starting and ending arc points of the two channels must be staggered, and the selected joint type.It has been proved by practice that the welding of titanium tube after sticking and fixing will fail due to the "memory" of titanium after a period of operation, and will not be affected by the corrosion of surrounding environment and stress corrosion.

In addition to meeting the relevant standards and specifications, welding shall also meet the following requirements:

(1) welding and group pairs must be carried out in a clean workshop or in an area free of iron pollution. Before any welding of titanium tubes, phenoline test must be conducted to confirm that there is no iron ion pollution (if the surface is polluted by iron ions, the filter paper will be orange).

(2) before welding, the fusion surface and the 50-mm wide area on each side of the weld shall be thoroughly cleaned with acetone or propanol or isopropanol to remove the oxide coating, corrosion, grease or other impurities affecting the quality of the welding joint.

(3) the welding wire is in accordance with AWS sfa-5.16 erti-2, with Fe content less than 0.05% and H content less than 60ppm. In titanium welding, argon with a purity of 99.99% is injected into the tube during root channel fusion. The interlayer temperature shall not be higher than 60°C.

Due to the harsh working conditions and special materials used in the PTA plant, the welding quality of the titanium tube condenser is required to be high. This project refers to ASMEK: welding skill assessment requirements in the qualification assessment of welding and brazing. Module tests are conducted before the start of the order to assess the skills of welders and welders.

At the same time, the wn75-100 standard specification of basf company was cited to test the relevant contents of the welding samples after the module test. The module test verified the qualification of the welding personnel and confirmed that the welding process was effective in controlling the defects.The module test, in addition, it is necessary to point out is, the introduction of ray back according to detection technology, can change the past module can cut thin RT test, and at the same time this technology can be applied to the finished tube sheet welding joint of conventional RT tests, thus more effectively increases the weld quality, for heat exchanger equipment safe operation to provide reliable guarantee for a long period of time.



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