What are the causes of corrosion failure in plate heat exchangers, as analyzed by heat exchanger manufacturers?
Release time:
2021-11-02 16:29
Source:
Heat exchanger manufacturers have different names according to customer requirements. But in fact, the processes are different. Whether it is fully welded or detachable, it is actually a plate heat exchanger. Today, the heat exchanger manufacturer will discuss the relevant knowledge of plate heat exchangers.
The heat transfer area of a plate heat exchanger consists of a series of corrugated plates, stacked between the frame plates and pressure plates to maintain the design pressure. The seals between the plates consist of gaskets.
To achieve higher thermal performance and very close temperatures, the fluids usually flow through the heat exchanger in a counter-current manner.
Various concavities, angles of herringbone patterns, and various shapes of corrugations are available on industrial production lines, carefully designed and selected to achieve better heat exchange effects and reduce pressure loss.
According to the working environment, pressure, and fluid properties, the welding method and required sealing materials are selected, and the materials and dimensions of each component are selected according to the results of thermal design and resistance calculation of the working pressure, thus ensuring the stable operation of the mining plate heat exchanger.
The heat exchanger manufacturer analyzed the five major causes of corrosion failure of plate heat exchangers:
1. Pitting Corrosion:
The heat exchanger manufacturer concluded that one type is local corrosion caused by the "occluded cell corrosion" effect, that is, the passivation film on the local metal surface is destroyed, forming perforations or corrosion pits with a size less than 1 mm. For example, if the surface of the stainless steel plate is rusted or scaled (carbide, silicate layer), the corrosion is caused by poor thermal conductivity and reduced medium pH value.
2. Stress Corrosion Cracking:
Under the action of static tensile stress and electrochemical medium, the cathodic dissolution process will cause local corrosion cracks or metal cracks. For example, when the formed plate is under pressure, residual internal stress will be generated, and contact with halogen ions (such as Cl-, f- ions, etc.) or H2S in the medium may lead to stress corrosion cracking.
3. Crevice Corrosion:
Spot or ulcer-like local corrosion caused by the "occluded cell corrosion" effect. The main difference from pitting corrosion is that due to the electrochemical inhomogeneity of the retained medium, corrosion occurs in the gaps of the metal parts. For example, corrosion on the bottom of the gasket groove or outside the corner hole seal gasket of the closed flow path of the thin plate.
4. Intergranular Corrosion:
Corrosion on the metal surface and deepening along the grain boundaries towards the interior will cause the loss of adhesion between grains, which will greatly reduce the strength of the material. For example, corrosion of stainless steel in the sensitive temperature range (400°C~600°C).
5. Other Corrosion Failures:
Mainly including leakage point corrosion, wear, microbial corrosion, etc. For example, hot steam containing acidic substances in contact with cold plates will cause leakage corrosion; the flow rate is too high at the inlet corners of the sheet material and the flow guiding area medium, or when the fluid contains gravel particles, it will cause wear; algae, bacteria and protozoa in seawater will cause microbial corrosion of the paper.
Therefore, when the heat exchanger manufacturer selects and calculates for the customer, it will ask the customer in detail about the working conditions and relevant technical parameters, and provide technical support for customizing durable and economical plate heat exchangers for the customer.
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