Does the appearance of localized rust spots on the fin surface mean the heat exchanger must be replaced? This is a question frequently raised by on-site technical engineers. The causes of rust spots may include coating damage, medium corrosion, or environmental humidity. The judgment should be based on sampling analysis and changes in operating parameters, not merely on appearance.
Fins are the main contributors to the heat transfer area of a tube-fin heat exchanger, and their surface condition directly affects the air-side heat transfer efficiency. During inspection, focus on observing the fin roots, tube sheet connections, and windward surfaces, and record the distribution range of rust spots and the area of coating peeling. If the rust spots are punctate and not continuous, cleaning and local repair may be performed first; if the peeled area exceeds 5% of the total fin area of a single tube bundle, or if the corrosion depth has caused fin thinning, sampling analysis should be conducted to determine the material corrosion type and evaluate whether material replacement or additional protective coating is needed. The GCH-132 fins are made of aluminum with anti-corrosion surface treatment, which can meet service requirements under normal operating conditions, but inspection intervals should be shortened in sulfur-containing or high-humidity environments.
An increase in pressure drop is often an early signal of fouling or blockage in the fin passages. It is recommended to record the inlet and outlet pressure difference and medium flow rate monthly. When the pressure difference rises by 15% above the initial value, purging or cleaning should be scheduled. During cleaning, avoid directing a high-pressure water gun directly at the fins to prevent fin deformation. Also monitor inlet and outlet temperature changes; if the heat transfer temperature difference continuously deviates from the design value, inspect the contact condition between the fins and tube walls. The GCH-132 uses an expansion joint process for tube-fin connection. After long-term thermal cycling, contact thermal resistance may increase, which can be assessed with the aid of thermal imaging.
When maintaining, replacing, or procuring additional units, four parameters should be provided to the supplier for thermal calculation: medium composition, flow rate, inlet and outlet temperatures, and allowable pressure drop. Note that structural parameters of the GCH-132, such as fin spacing and number of tube rows, are determined according to project data at the contract stage and should not be directly copied from general catalogs. If the medium contains corrosive components, the fin material and coating requirements should be specified in the technical agreement, and the sampling and testing method for acceptance should be agreed upon.
When shutdown exceeds one month, the medium inside the tubes should be drained, and the fin surface should be cleaned and kept dry. If the ambient humidity is high, a temporary protective agent may be sprayed on the fin surface and removed before restart. After reinstallation of a heat exchanger that has been shut down for a long time, it should first be operated at low pressure to check for leaks, then gradually raised to design conditions.
