During the operation of shell-and-tube heat exchangers, problems of varying degrees often arise. Regular inspection of the heat exchanger is essential to resolve issues promptly and ensure the normal progress of production. When a problem occurs in a shell-and-tube heat exchanger but the root cause cannot be identified, how should inspection and troubleshooting be conducted?
I. Precautions for the Installation of Shell-and-Tube Heat Exchangers
1. Pressure Testing Must Be Conducted Before Installation
The heat exchanger must undergo a hydrostatic test at a pressure 1.5 times the working pressure. For the steam section, the test pressure shall not be lower than the steam supply pressure plus 0.3 MPa; for the hot water section, it shall not be lower than 0.4 MPa. Under the test pressure, the pressure should remain stable without dropping for 10 minutes.
2. Sufficient Construction Space and Access Channels Must Be Reserved During Installation
In the installation space, an area for extracting and removing the tube bundle shall be reserved at the front end of the shell-and-tube heat exchanger. Specifically, the distance from the head to the wall or roof shall not be less than the length of the heat exchanger. The net width of the operating channel for equipment operation shall not be less than 0.8 meters. Sufficient operating space is conducive to disassembly and maintenance.
3. Instruments and Meters Installed on the Heat Exchanger Must Be Visible
It is mandatory to install instruments and meters on the heat exchanger in a way that facilitates inspection and monitoring. The installation height of various valves and instruments shall be convenient for operation and observation, ensuring that any problems can be detected and resolved promptly.
4. There Are Corresponding Requirements for Vertical Space Distance
The vertical net distance from the highest point of the accessories on the upper part of the heater to the lowest point of the building structure shall meet the requirements for installation and inspection, and shall not be less than 0.2 meters. This requirement is intended to facilitate maintenance work.
II. Precautions for the Inspection of Shell-and-Tube Heat Exchangers
1. Fouling on Tube Wall Surfaces
(1) Particulate Fouling
The accumulation of solid particles suspended in the fluid on the heat transfer surface. This type of fouling also includes sediment layers formed by larger solid particles on horizontal heat transfer surfaces due to gravity (so-called sedimentary fouling) and the deposition of other colloidal particles.
(2) Crystalline Fouling
Deposits formed by the crystallization of inorganic salts dissolved in the fluid on the heat transfer surface, usually occurring during supersaturation or cooling. Typical examples include scaling layers of calcium carbonate, calcium sulfate, and silicon dioxide on the cooling water side.
(3) Chemical Reaction Fouling
Fouling generated by chemical reactions on the heat transfer surface. The material of the heat transfer surface does not participate in the reaction but may act as a catalyst for the chemical reaction.
(4) Biological Fouling
Except for seawater cooling systems, biological fouling generally refers to microbial fouling. It may produce slime, which in turn provides conditions for the reproduction of biological fouling. This type of fouling is highly sensitive to temperature; under suitable temperature conditions, biological fouling can form a layer of considerable thickness.
(5) Freezing Fouling
Fouling formed by the solidification of fluid on the supercooled heat transfer surface. For example, when water is below the freezing point and freezes into ice on the heat transfer surface. The uniformity of temperature distribution has a significant impact on this type of fouling.
2. Leakage of Shell-and-Tube Heat Exchangers
(1) Repair of Minor Tube Bundle Leakage
If only a few tubes are leaking and the leakage does not affect operation, plugs can be used to block the leaking tubes to prevent the leakage from impairing heat exchange efficiency.
(2) Repair of Massive Tube Bundle Leakage
Massive tube bundle leakage will significantly reduce heat exchange efficiency, requiring the replacement of the tube bundle with a new one. Generally, formal manufacturers have a sound after-sales service mechanism and will send professional technicians to provide on-site maintenance.
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