A, two media string each other (internal leakage)
1 Generate causes
① heat exchanger tube corrosion perforation, cracking.
② heat exchanger tube and tube plate expansion mouth (weld mouth) cracked.
③ floating head type heat exchanger floating head flange seal leakage.
2 processing methods
① replace or plug the leaky heat exchanger tube.
② heat exchanger tube and tube plate re-expansion (welding) or plugging.
③ tighten the bolts or replace the sealing gasket.
Second, the flange at the seal leakage
1 Cause
① gasket under pressure, corrosion, deterioration.
② Insufficient bolt strength, loosening or corrosion.
③ flange rigidity and sealing surface defects.
④ flange is not flat or misaligned, gasket quality is not good.
2 Processing method
①Tighten the bolts and replace the gaskets.
②Upgrade the bolt material, tighten the bolt or replace the bolt.
③Replace the flange or deal with the defect.
④Reassemble or replace the flange and replace the gasket.
Poor heat transfer
1 Causes
①Heat exchange tube scaling.
②Bad water quality, oil and microorganisms.
③Separator short circuit
2 Treatment method
①Chemical cleaning or jet cleaning of dirt and grime.
②Strengthen filtration, purify media and strengthen water quality management.
③Replace the tube box gasket or replace the bulkhead.
Fourth, the resistance drop exceeds the allowable value
1 Cause
Scaling inside the shell, inside and outside the tube
2 Treatment method
Use jet or chemical cleaning scale
V. Serious vibration
1 Generated by
① Resonance caused by the frequency of the medium.
② Resonance caused by external pipe vibration.
2 Treatment method
①Change the flow rate or change the inherent frequency of the pipe bundle.
② Reinforce the pipe to reduce vibration.
Plate heat exchanger common failure causes analysis and processing methods
Plate heat exchanger common failures are string liquid, external leakage, excessive pressure drop, the heating temperature can not meet the requirements of four aspects.
A series of liquid
1 cause
① due to improper selection of plates resulting in plate corrosion cracks or perforations.
②The operating conditions do not meet the design requirements.
③ the residual stress of the plate after cold stamping and forming and the assembly of the clamping size is too small to cause stress corrosion.
④ Slight leakage at the leakage groove of the plate, resulting in the concentration of harmful substances in the medium corrodes the plate and forms a string of liquid.
2 Treatment methods
①Replace the cracked or perforated plate, and find the cracked plate in the field with the light transmission method.
② adjust the operating parameters so that they reach the design conditions.
③ heat exchanger maintenance assembly clamping size should meet the requirements, and not the smaller the better.
④ plate material reasonable match.
Second, external leakage
1 cause
① clamping size is not in place, the size of each uneven (the size of each deviation should not be greater than 3 mm) or loose clamping bolts.
② Part of the gasket is out of the sealing groove, the main sealing surface of the gasket is dirty, the gasket is damaged or the gasket is aging.
③ Plate deformation, assembly misalignment caused by running gasket.
④ Cracks in the sealing groove area of the plate or the second sealing area.
2 Treatment method
① In a non-pressure state, re-clamp the equipment according to the clamping size provided by the manufacturer, the size should be uniform and the deviation of the clamping size should be no more than ±0.2N (mm) (N is the total number of plates), the parallelism between the two clamping plates should be kept within 2 mm.
② mark on the external leakage parts, and then the heat exchanger disassembly one by one to solve, reassemble or replace the gasket and plate.
③ Dismantle the heat exchanger and repair the deformed parts of the plates or replace them. In the absence of spare parts for the plates, the deformed parts can be temporarily removed and reassembled for use.
④ When reassembling the disassembled plates, the plate surface should be cleaned to prevent dirt from adhering to the gasket sealing surface.
3. Excessive pressure drop
1 Causes
① operation system pipeline is not normal blowing, especially the new installation system pipeline in many dirty things (such as welding slag, etc.) into the internal plate heat exchanger, due to the plate heat exchanger flow channel cross-sectional area is narrow, the heat exchanger within the sediment and suspended matter gathered in the corner hole and guide flow area, resulting in the flow channel area is greatly reduced, resulting in the main loss of pressure in this part.
② The plate heat exchanger is selected for the first time when the area is small, resulting in a high flow rate between the plates and the pressure drop is large.
③ plate heat exchanger running after a period of time, due to plate surface fouling caused by excessive pressure drop.
2 processing methods
① Clear the heat exchanger runners in the dirt or plate scaling, for the new operation of the system, according to the actual situation once a week cleaning.
② secondary circulation water is best used after softening treatment of soft water, the general requirements of the water quality concentration of suspended matter is not greater than 5 mg / L, impurity diameter is not greater than 3 mm, pH ≥ 7.
When the water temperature is not greater than 95 ℃, Ca, Mg concentration should not be greater than 2 mmol / L;
When the water temperature is greater than 95 ℃, Ca, Mg concentration should not be greater than 0.3 mmol / L, dissolved oxygen quality concentration should not be greater than 0.1 mg / L.
③ For the centralized heating system, the method of primary to secondary water replenishment can be used.
Fourth, the heating temperature can not meet the requirements
1 Causes
①Insufficient flow of medium on the primary side, resulting in large temperature difference and small pressure drop on the hot side.
②Low temperature on the cold side, and low temperature at the cold and hot end.
③Multiple plate
Heat Exchangers operating in parallel with uneven flow distribution.
④ internal scaling of the heat exchanger is serious.
2 Treatment methods
① Increase the flow rate of the heat source or increase the diameter of the heat source media pipeline.
② Balance the flow of multiple plate heat exchangers running in parallel.
③ disassemble the plate heat exchanger to clean the plate surface scale.
I. Tube bundle failure
1, the corrosion of the tube bundle, wear caused by tube bundle leakage or blockage caused by scaling in the tube bundle failure
Cooling water contains iron, calcium, magnesium and other metal ions and anions and organic matter, active ions will make the cooling water corrosion enhanced, the presence of metal ions cause hydrogen or oxygen depolarization reaction thus leading to tube bundle corrosion. At the same time, as the cooling water contains Ca2+ and Mg2+ ions, it is easy to scale at high temperatures for a long time and block the tube bundle.
In order to improve the heat transfer effect and prevent the tube bundle from corrosion or blockage, the following methods are adopted:
(1) Add scale inhibitor to the cooling water and clean it regularly.
For example, the cooling water of the gas cooler uses an ion electrostatic processor or adds scale and corrosion inhibitor and algaecide to remove dirt and reduce the hardness of the cooling water, thus reducing the degree of tube bundle scaling.
(2) Keep the fluid flow rate in the tube stable.
If the flow rate increases, the thermal conductivity becomes larger, but the wear and tear will also increase accordingly. Minsheng Coal Chemical has modified the groundwater pump with frequency conversion, so that the pressure of the groundwater network is more stable, which improves the heat exchange effect of the heat exchanger and reduces the corrosion of the tube bundle.
(3) Choose corrosion-resistant materials (stainless steel, copper) or increase the wall thickness of the tube bundle.
(4) When the end of the tube is worn, the tube bundle can be protected by accessing synthetic resin etc. in the 200mm length of the inlet.
2.Vibration caused by the failure
Causes of vibration include
Vibration of the tube bundle caused by the vibration of pumps and compressors; pulsations generated by rotating machinery;
The impact of high speed fluids (high pressure water, steam etc.) flowing into the bundle on the bundle.
The following methods are often used to reduce the vibration of the tube bundle:
(1) Minimising the number of starts and stops.
(2) At the inlet of the fluid, install adjustment slots to reduce the vibration of the bundle.
(3) Reduce the baffle spacing to reduce the amplitude of the bundle.
(4) Minimise the aperture of the bundle through the baffle.
Flange leakage into
Flange leakage is due to the rise in temperature, fastening bolts heat elongation, in the fastening parts of the gap caused by.
Therefore, after the heat exchanger is put into use, the flange bolts need to be re-fastened.
The fluid in the heat exchanger is mostly toxic, high-pressure, high-temperature substances, once the leakage is easy to cause poisoning and fire accidents.
Special attention should be paid to the following points in the daily work:
Minimise the number of gaskets used and the use of metal gaskets;
The use of methods of tightening gaskets under internal pressure;
Use of easy fastening methods.
Source: Reproduced
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