Why Testing the Water Pressure after Overhauling the Heat Exchanger?
The purpose of the pressure test after maintenance is to check whether the heat exchanger has the ability to withstand the design pressure safely (i.e. the compressive strength), the tightness, the quality of the interface or joint, the welding quality and the tightness of the sealing structure.
In addition, the residual deformation of the base metal weld of the vessel and pipeline can also be observed to timely find the problems existing in the material.
Briefly describe the pressure test and maintenance sequence of the heat exchanger:
The pressure test is an important part of heat exchanger maintenance. Different types of shell-and-tube heat exchangers have different pressure test sequences. The floating head type is used as an example to illustrate the sequence of maintenance and pressure test.
1. Prepare the purge tool → remove the outer head, tube box and flange at the float end → remove the inner head at the float end → remove the tube bundle → inspect and clean.
2. Prepare gaskets, blind plates and pressure testing tools → install tube bank → install tube box and install false float head (used as temporary head) shell flange with blind plate → inject water into the shell side → assemble pressure testing pipeline → Test pressure (I) Check the expansion of tube mouth and heat exchange tube → remove false float head and install inner float head and blind plate cover.
3. Add a blind plate to the box flange → inject water into the pipe side and assemble pressure test line → test pressure (2) check the gaskets and tubes at the float end → install the outer head at the float end → inject water into the shell side → test pressure (3) check the seal of the shell → remove the blind plate and fill in the inspection card.
The pressure test (1) aims to check whether the heat exchange tube is broken and whether the expansion interface leaks. If the pipe is broken after pressure release, plug or replace it; if the expansion joint has leakage and pressure relief, perform supplemental expansion, but the number of supplementary expansions should not exceed 3 times, otherwise, a new tube should be replaced. After the treatment of each defect, pressurize the test again until it is qualified.
The purpose of pressure test (2) is to check the installation quality, mainly to check the inner head gasket and tube bundle of the floating head. If leakage is found in the gasket, the reason should be analyzed and properly handled.
The pressure test (3) is the overall pressure test of the equipment, which mainly checks the installation quality of the outer head of the floating head.
What are the sequence and requirements of the pressure test?
(4) When the test pressure on the pipe side is higher than the shell side pressure, the test pressure value shall be according to the drawings or the method agreed by both the production and construction units.
(5) Threaded locking ring heat exchanger
① Shell side pressure test (test pressure is not greater than the maximum test pressure difference), check the shell, heat exchange tube, tube plate joints, and related parts.
② Step pressure test of tube side and shell side (the test pressure and pressure test procedures are carried out according to the design regulations); check the sealing disc and other parts.
(6) After the pressure test, the accumulated water inside the heat exchanger shall be drained and dried if necessary.
What are the sequence and requirements of the pressure test?
(1) Fixed tube plate
① Shell pressure test: check the connection between shell, heat exchange tube and tube plate and the relevant parts.
②Pipe pressure test: check the pipe box and related parts.
(2) U-shaped tube heat exchanger, kettle-type reboiler (with U-shaped tube bundle) and packing box type heat exchanger
① Shell side pressure test (with test pressure ring), check the connection parts of the shell, tube sheet, heat exchange tube and related parts.
② Pressure test in the piping process, check the relevant parts of the pipe box.
(3) Floating head type heat exchanger, kettle type reboiler (with floating head type tube bundle)
①Use the test pressure ring and special tool for floating head to test the pressure of the pipe and tube plate joint. For the kettle-type reboiler, a special shell for pressure test of the tube and tube sheet joints should also be equipped to check the heat exchange tube and tube sheet joints and related parts.
② Pressure test in the pipeline, check the tube box, floating headcover and related parts.
③ Shell side pressure test, check the shell, heat exchange tube and tube plate joints and related parts.
In addition, the residual deformation of the base metal weld of the vessel and pipeline can also be observed to timely find the problems existing in the material.
Briefly describe the pressure test and maintenance sequence of the heat exchanger:
The pressure test is an important part of heat exchanger maintenance. Different types of shell-and-tube heat exchangers have different pressure test sequences. The floating head type is used as an example to illustrate the sequence of maintenance and pressure test.
1. Prepare the purge tool → remove the outer head, tube box and flange at the float end → remove the inner head at the float end → remove the tube bundle → inspect and clean.
2. Prepare gaskets, blind plates and pressure testing tools → install tube bank → install tube box and install false float head (used as temporary head) shell flange with blind plate → inject water into the shell side → assemble pressure testing pipeline → Test pressure (I) Check the expansion of tube mouth and heat exchange tube → remove false float head and install inner float head and blind plate cover.
3. Add a blind plate to the box flange → inject water into the pipe side and assemble pressure test line → test pressure (2) check the gaskets and tubes at the float end → install the outer head at the float end → inject water into the shell side → test pressure (3) check the seal of the shell → remove the blind plate and fill in the inspection card.
The pressure test (1) aims to check whether the heat exchange tube is broken and whether the expansion interface leaks. If the pipe is broken after pressure release, plug or replace it; if the expansion joint has leakage and pressure relief, perform supplemental expansion, but the number of supplementary expansions should not exceed 3 times, otherwise, a new tube should be replaced. After the treatment of each defect, pressurize the test again until it is qualified.
The purpose of pressure test (2) is to check the installation quality, mainly to check the inner head gasket and tube bundle of the floating head. If leakage is found in the gasket, the reason should be analyzed and properly handled.
The pressure test (3) is the overall pressure test of the equipment, which mainly checks the installation quality of the outer head of the floating head.
What are the sequence and requirements of the pressure test?
(4) When the test pressure on the pipe side is higher than the shell side pressure, the test pressure value shall be according to the drawings or the method agreed by both the production and construction units.
(5) Threaded locking ring heat exchanger
① Shell side pressure test (test pressure is not greater than the maximum test pressure difference), check the shell, heat exchange tube, tube plate joints, and related parts.
② Step pressure test of tube side and shell side (the test pressure and pressure test procedures are carried out according to the design regulations); check the sealing disc and other parts.
(6) After the pressure test, the accumulated water inside the heat exchanger shall be drained and dried if necessary.
What are the sequence and requirements of the pressure test?
(1) Fixed tube plate
① Shell pressure test: check the connection between shell, heat exchange tube and tube plate and the relevant parts.
②Pipe pressure test: check the pipe box and related parts.
(2) U-shaped tube heat exchanger, kettle-type reboiler (with U-shaped tube bundle) and packing box type heat exchanger
① Shell side pressure test (with test pressure ring), check the connection parts of the shell, tube sheet, heat exchange tube and related parts.
② Pressure test in the piping process, check the relevant parts of the pipe box.
(3) Floating head type heat exchanger, kettle type reboiler (with floating head type tube bundle)
①Use the test pressure ring and special tool for floating head to test the pressure of the pipe and tube plate joint. For the kettle-type reboiler, a special shell for pressure test of the tube and tube sheet joints should also be equipped to check the heat exchange tube and tube sheet joints and related parts.
② Pressure test in the pipeline, check the tube box, floating headcover and related parts.
③ Shell side pressure test, check the shell, heat exchange tube and tube plate joints and related parts.
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