What are the causes, factors and protective measures affecting the wear rate of shell and tube heat exchangers?

- Sep 25, 2019-

Shell and tube heat exchangers are widely used and have a wide range of types. Faced with various shell and tube heat exchanger wear and tear, many customers do not know how to start or caught off guard. What are the factors affecting the wear of shell and tube heat exchangers? Following is some information about what factors lead to the wear rate of shell-and-tube heat exchangers in Guangzhou. I hope it will be helpful.

Wear Reasons of Shell and Tube Heat Exchangers

In the heat exchanger, the tube passes through the baffle with a gap. The flow of fluid in the shell will induce the vibration of the tube. At this time, both the tube and the baffle will be worn. When the baffle is thin and hard, the wear rate of the shell-and-tube heat exchanger is faster. In practice, the relative motion between the tube and the baffle plate caused by vibration is very complicated, because the vibrating tube will repeatedly contact or detach from the baffle plate, that is, there are sliding and obvious impact. Here, the wear process from the attached metal to the oxide layer consists of the following stages: the surface layer is loosened, adhered, elastic deformation and metal transfer due to vibration, and the debris is oxidized to form an intermediate layer. Then the loose debris is produced by wear. The loose abrasive particles are easily carried away by the fluid. This accelerates wear and tear, so that the cycle proceeds until wear and tear breaks down.

Factors Influencing Wear Rate

1. Shell and Tube Heat Exchanger Composite Materials

1) When the tube and the baffle take the same material, the wear rates of the two materials are approximately equal.

2) The performance of refractories, when the baffle material is harder than the tube, the tube will be worn faster.

2. Gap Vibration Step Rate and Amplitude of Tube and Baffle Hole

Amplitude, vibration frequency and gap vibration step rate and amplitude of tube and baffle tube hole have great influence on wear impact. The wear amount increases with the increase of amplitude and percentage. Because the kinetic energy of tube increases with the increase of amplitude and frequency, the impact kinetic energy increases, which accelerates the impact wear and adhesion wear.

3. Geometric structure and material properties of impact surface

The geometric dimensions of the tube (wall thickness, pipe diameter, boundary conditions, etc.) and the baffle plate (plate, hole diameter, baffle spacing, etc.) as well as the material properties of the tube and baffle will affect the wear of the tube.

It has been found through experiments that when there is wax in the gap between the tube and the orifice of the baffle, there will be no impact noise. This is because wax makes the gap between the tube and the baffle hole smaller; wax also has lubrication effect, so it greatly cushions the vibration. In production practice, such as heat exchangers in refineries, because the medium lubrication is better, the wear is not so serious. When the medium has}''n property, the wear will increase significantly.

Wear Protection Measures for Shell and Tube Heat Exchangers

(1) The grinding rate can be reduced by using the following enlargement and maintenance applications.

(2) Selection of mutual insoluble metal material combination for limited side bonding grinding

(3) coating protection: lubrication protection, surface film protection and other interface protection can reduce wear.

(4) Conversion protection: Select suitable hardness, roughness and contact resistance of "metal pair" to convert wear and tear into allowable level.

(5) Reducing the airing between the tube and the baffle hole can significantly reduce the abrasion. If the airing between the tube and the baffle hole is reduced to half of the original one, the abrasion basin will be reduced to the original one.

(6) Wear can also be reduced by winding strips and rolling rods (plates or wedges) between pipes to prevent vibration of pipes.

The baffle rod heat exchanger is selected. Because the baffle rod grid is installed between the tubes, there is no gap between them, thus eliminating or greatly reducing the vibration.