Tail sealing of electric heating cables

　　The electric accompanied by the tropical system in petrochemical industry, municipal heating and other fields of wide application, make its operation reliability pay attention to. As the key link of the system, the end sealing bears the important function of preventing moisture from intruding and guaranteeing electrical safety. According to statistics, about 35% of the electric accompanied by the tropical failure originated from the insulation failure caused by the bad seal of the tail end. Therefore, in-depth study of electric accompanied by tropical tail sealing technology, to enhance the overall reliability of the system is of great significance.

　　First, the technical requirements of the tail seal

　　The electric accompanies the tropical tail end seal to meet three basic technical requirements:

　　1. electrical insulation: sealing material volume resistivity should be greater than 1×10¹²Ω-cm

　　2. environmental tolerance: need to resist -40 ℃ to 120 ℃ temperature changes and ultraviolet radiation

　　3. Mechanical protection: should have a tensile strength of ≥ 10MPa mechanical properties

　　Comparison of mainstream sealing methods

　　1. Heat-shrinkable tube sealing method

　　Adopting double-layer structure heat-shrinkable tube, the inner layer is adhesive layer, the outer layer is polyolefin protective layer. Typical construction parameters:

　　Heating temperature: 120-150℃; shrinkage rate: ≥50%; applicable pipe diameter: Φ8-25mm

　　The advantage is convenient construction, but there is a risk of aging of the adhesive layer in long-term use.

　　2. Epoxy resin sealing method

　　Use two-component epoxy resin casting sealing, key technical indicators:

　　Curing time: 24 hours at 25℃; insulation strength: ≥30kV/mm; temperature resistance level: -50℃ to 155℃.

　　This method has the best sealing effect, but the construction is complicated and irreversible.

　　3. Specialised terminal sealing method

　　Adopting standardised sealing terminals, typical features:

　　Protection grade: IP68; Installation time: ≤5 minutes/pc; Reuse: up to 5 times

　　Suitable for batch installation, but the cost is high.

　　Third, sealing programme selection criteria

　　According to the differences in the application environment, the sealing programme selection should follow the following criteria:

　　1. humid environment: priority selection of epoxy resin sealing

　　2. corrosive environment: recommended to use fluorine rubber material terminal

　　3. temporary works: apply heat shrinkable tube programme

　　4. high-risk areas: explosion-proof sealing terminals must be used

　　Fourth, construction quality control points

　　Ensure the quality of the end sealing need to control the three key links:

　　1. Pre-treatment stage:

　　Notch flatness deviation ≤ 0.5mm; cleanliness requirements without visible contaminants

　　2. Construction stage:

　　Heat-shrinkable tube axial overlap ≥ 10mm; epoxy resin pouring full without bubbles

　　3. Acceptance stage:

　　Insulation resistance test ≥ 100MΩ; sealing test (0.3MPa/30min without leakage)

　　V. Common problems and solutions

　　1. Water seepage at the sealing place

　　Cause: material shrinkage or curing incomplete

　　Countermeasure: Make up the second sealing, use silicone to strengthen it.

　　2. Decrease in insulation resistance

　　Cause: conductive pollutants at the interface

　　Countermeasure: alcohol cleaning and re-sealing

　　3. Mechanical damage

　　Cause: external impact or abrasion

　　Countermeasure: add stainless steel protective sleeve

　　Electric accompanied by tropical end sealing is to ensure the long-term reliable operation of the system is the key link. Three mainstream sealing methods have their own characteristics, engineering selection should be comprehensively considered environmental conditions, cost budget and operation and maintenance requirements and other factors. In the future, with the development of new material technology, self-healing sealing materials and intelligent monitoring terminal application will further enhance the reliability of the sealing system.