When JHR-35 sheathed electric heaters are used for pipeline heat tracing and medium insulation, maintenance work is often more easily overlooked than selection. Two types of problems are frequently reported on site: one is uneven pipeline surface temperature, and the other is short-term pitting of the sheath. Both phenomena are directly related to sheath material, power configuration, and installation method, and room for handling them needs to be reserved at the design and selection stage.
Uneven Surface Temperature: First Check Fit and Power Distribution
The heat from a sheathed electric heater must be conducted through the sheath wall to the pipeline surface. If there is a gap or poor fit between the sheath and the pipeline, the local heat transfer resistance increases, and the surface temperature will show obvious differences. During maintenance, check whether the sheath installation is secure and whether there is an oxide layer or foreign matter on the contact surface. For long-distance pipelines, the power of a single heater is limited, so it is advisable to configure heaters section by section along the pipeline to avoid excessively high power density in one section and insufficient heat in adjacent sections. Carbon steel sheaths have good heat transfer performance and are suitable for low-corrosion, high-heat-transfer demand scenarios, helping to reduce temperature differences. If a large temperature difference has already occurred on site, calculate whether power compensation is sufficient based on the pipeline's heat dissipation conditions, rather than simply raising the set temperature.
Sheath Pitting: Matching Material Selection with Operating Environment
Short-term pitting of the sheath is usually related to medium corrosiveness, surface deposits, and local overheating. In highly corrosive environments, stainless steel sheaths should be selected, but the thermal conductivity of stainless steel is lower than that of carbon steel, so power must be increased accordingly during selection to compensate for heat transfer loss. Otherwise, if the heater operates at full load for a long time, the sheath surface temperature will be too high, which instead accelerates the corrosion process. During maintenance, if pitting is found concentrated on one side, check whether there is liquid accumulation, scaling, or airflow erosion on that side, and adjust the installation angle and protective measures if necessary. Pitted areas should not simply be repaired by welding and then put back into use; whether to replace them should be evaluated based on wall thickness measurement.
Arrangement of Maintenance Cycles and Inspection Items
Maintenance cycles should be determined according to the medium corrosion level and operating temperature. A common practice is to regularly measure the sheath surface temperature distribution and record the deviation at each measuring point; check the wiring terminals and insulation resistance to confirm there is no moisture or looseness; and visually inspect the sheath appearance, focusing on welds, flange connections, and support locations. The temperature control loop should also be included in the inspection scope. A decline in temperature control accuracy will cause the heater to start and stop frequently, indirectly affecting sheath life. For equipment that has been in operation for a long time, the sheath wall thickness can be measured during shutdown opportunities, and trend records can be established to provide a basis for replacement decisions.
Reserve Margin for Maintenance at the Selection Stage
When determining the parameters of JHR-35 sheathed electric heaters, design and selection personnel should consider corrosion allowance and power adjustment margin in addition to meeting the heat load under normal operating conditions. Selecting stainless steel sheaths and adding power compensation for highly corrosive environments, and selecting carbon steel sheaths and controlling surface load for low-corrosion scenarios, are both effective ways to reduce later maintenance frequency. The installation location should be easy to disassemble and inspect, and heaters should not be arranged in pipeline sections that are difficult to access. Maintenance convenience itself is also an implicit indicator in selection. Only with sufficient consideration in the early stage can uneven temperature and pitting problems be discovered and handled in a more timely manner later.
