During commissioning of the heat transfer oil pipeline, slow heating and uneven surface temperature occurred. After troubleshooting, it was confirmed that the contact area between the heater sheath and the oil was insufficient—this on-site phenomenon indicates that the maintenance and installation details of sheathed electric heaters directly affect heat exchange performance. The following Q&A summarizes the verification points that procurement personnel need to pay attention to.
Q: What consequences will insufficient contact area between the sheath and the oil cause? How can it be prevented from a procurement perspective?
A: When the contact area is insufficient, heat cannot be fully transferred to the oil, manifesting as a decreased heating rate and uneven surface temperature. When verifying the installation space, procurement personnel should confirm that the effective heat exchange length of the sheath matches the inner diameter of the pipeline, avoiding excessively high local heat flux density caused by a short sheath or insufficient insertion depth. At the same time, attention should be paid to the compatibility between the sheath material and the oil to prevent the thickening of the coking layer from further weakening heat transfer. For occasions where abnormal heating has already occurred, first check whether there is carbon deposition or scaling on the sheath surface, and then recheck the installation position.
Q: How should the on-site handling be carried out when the insulation of the electric heating element decreases after dampness?
A: If the measured insulation resistance is low, power should not be applied directly. The electric heating element can be placed in an oven at about 200°C for several hours of drying, or heated by applying power at a reduced voltage, until the insulation performance recovers. When signing technical agreements, procurement personnel can require the supplier to specify the acceptance limit of insulation resistance and handling recommendations after dampness, so that incoming inspection and warehouse management have a basis to follow.
Q: What other verification items are easily overlooked in daily maintenance?
A: First, the matching of supply voltage and power to avoid overvoltage operation shortening the element life; second, the sealing status of the wiring cavity to prevent oil contamination and moisture intrusion; third, regularly clean the attachments on the sheath surface to maintain heat transfer efficiency. In the procurement process, the above maintenance points can be included in the list of accompanying documents, requiring the supplier to provide clear installation and maintenance instructions.
