Fluoropolymer Heaters

1) Fluoropolymer sheath melted, split or distorted.
CAUSE	SOLUTION
Heater operated with low liquid level without proper thermal protection. Check/test wiring and thermal protector to verify operation.	Repair/replace heater as required.
Heater operated at higher than rated voltage. Check/verify power supplies and compare to nameplate rating of element.	Correct voltage and replace heater as required.
Viscous or concentrated solution. Dense or concentrated solutions impede heat flow from the elements and can cause localized overheating and damage to the fluoropolymer sheath.	Increased mixing of the solution near the element can reduce the problem but replacement of the heater with a de-rated/more open design is preferable.
Buildup on the sheath. Any buildup between the formed passes on a Fluoropolymer heater will cause localized overheating and can cause melting of the sheath material.	Periodic cleaning can reduce the buildup and overheating. Open type designed, over-the-side model heaters should also be considered as replacement options. Vari-power heaters can be considered for low power requirement installations. Bottom designs with tight spacing should be avoided in any application where buildup or sedimentation is possible.
Operation in liquids that polymerize or crystallize when heated. Buildup on the fluoropolymer sheath will limit heat transfer, causing localized overheating which may melt the sheath.	These solutions can only be heated with de-rated heaters or through indirect type heating methods. Either replace heaters with open, derated design (2.5 WSI or less) or switch heating methods.
Thermal protector pulled up out of position during installation or replacement. The thermal protector only measures the sheath temperature directly adjacent to where it is mounted.	The thermal protector must be fully seated into base of the thermal well to work properly.Verify installation of thermal protector. Replace heater as required.
Thermowell tubes full of solution. Any fluid inside the Thermowell will act as a coolant and delay the switching point of the protector device until the fluid is boiled away. Care should be taken to ensure the well is not damaged, the heater junction box is sealed properly, and that the excessive moisture is prevented from entering.	Periodic inspection of the interior of the junction box and thermal well should be considered in unusually wet installations or in solutions operating over 180 degrees F. If solution is found in the Thermowell, a pressure test (5 PSI) should be performed to verify integrity.
Thermowell retainer bracket removed, out of position or damaged. Since the retainer bracket holds the thermal protector against the element at the top of the hotzone, damage to or misalignment can affect the response time and performance of the protector.	Reposition the bracket and Thermowell if heater is serviceable. Replace heater if necessary.
Localized overheating caused by operation in a confined area. If fluoropolymer heaters are operated in too small of an area that effectively limits their ability to dissipate the energy they produce, localized overheating and melting may occur.	The heater should either be moved to a more open area or solution circulation should be added to assist in heat transfer. Replace heater if necessary.
Improper forming clearance or compressed passes on the element. Formed elements should not be contacting adjacent passes under any type of pressure. While incidental element contact normally will not cause problems, compressed elements in high temperature or viscous fluids will cause excessive localized overheating and melting.	Usually element contact spots can be opened up by hand forming. If contact pressure remains the element should be returned to factory.
2) Swelled or split heater sheath (any location).
CAUSE	SOLUTION
Usually caused by damage to the fluoropolymer sheath near the swelled area, which allows solution to enter and chemically attack the heater sheath. Solution then saturates the magnesium oxide insulation and hydraulically expands the insulation as it converts to magnesium hydroxide.	Determine the cause of damage and replace the heater with a guarded model. See section 3, "Damage to fluoropolymer sheath" (third item).
3) Swelled or split heater sheath at the hot zone transition. This condition can be caused by one or more the following conditions.
CAUSE	SOLUTION
Low liquid level. Operating an element out of solution for a short period of time without the thermal protector connected will cause swelling or melt damage to the fluoropolymer covering. Solution can then enter, corrode the heater sheath and hydraulically expand the element.	Recommend the use of thermal protection devices and liquid level controls with replacement heaters.
Repeated low level incursions. Repeated low level conditions even with a thermal protection device will cause degradation of the fluoropolymer sheath and increased permeability in any exposed area. Moisture or chemistry can then permeate through the damaged area and will be concentrated at the hotzone transition point. Over time this fluid will cause corrosion and hydraulic expansion failure in this area.	Recommend the use of liquid level controls with replacement heaters to prevent repeated low level exposure.
Damage to the fluoropolymer sheath. Cuts, nicks or damage to the fluoropolymer sheath at any location will allow solution to come in contact with the exposed heater sheath. This heated fluid will vaporize and tend to condense at the hotzone transition point. Over time, this fluid will cause corrosion, sheath penetration and hydraulic expansion failure in this area.	Recommend careful handling and the use of guards on replacement heaters to reduce the incidence of damage.
High solution level. High solution levels, which allow contact with the junction box, can break down the epoxy and internal seals and allows solution to enter the element. This fluid may cause an electrical short circuit and will cause corrosion of seals and the element with a resultant hydraulic expansion failure in this area.	Replacement heaters should be blocked up slightly to prevent reoccurrence or solution level should be maintained at an appropriate level.
Improperly sealed flex lead junction. Fluoropolymer heaters will develop a positive internal pressure between the metal element and fluoropolymer sheath when energized and a partial vacuum while cooling. Improperly sealing the end of a flex lead option heater will allow moist air to enter and condense on the element during this cooling cycle. This moisture will accumulate over time at the flex lead/hotzone transition causing damage to the electrical connections and hydraulic expansion and failure of the insulation.	Replacement heaters must be properly installed by user to prevent this damage from reoccurring. Rigid risers or the use of small potted junction boxes can alleviate this problem as well.
4) Section of element that's completely missing.
CAUSE	SOLUTION
Usually caused by combination of physical damage to the fluoropolymer sheath and corrosion on the element. Subsequent arcing and electrical discharges melt away section of the element until the electrical protectors open.	Properly sized protectors, good grounding and the use of GFCI circuits will reduce the potential of this type of failure.
5) Melting or distortion of junction box at the element insertion point.
CAUSE	SOLUTION
Usually caused by moisture within element insulation which condenses on interior of epoxy seals creating a current path to ground. Large current flow in this area heats the element melting the junction box and surrounding epoxy sealant.	Properly sized protectors, good grounding and the use of GFCI circuits will reduce the potential of this type failure.
6) Cracks in internal epoxy encapsulation.
CAUSE	SOLUTION
Usually caused by an electrical discharge between the element and ground or between phases of the power connection.	Check heaters for damage to the element sheath or for indications of high fluid levels, which may have caused solution leakage (see section 3, "Damage to fluoropolymer heater sheath", third item). Replace heater as required.
7) Holes in the Thermowell tube.
CAUSE	SOLUTION
Moisture or fluid entering the junction box and migrating to and accumulating in the Thermowell will degrade the thermal protector allowing a current path and arcing to occur to the thermal well tube. Any fluid inside the Thermowell will also act as a coolant and delay the switching point of the protector device until the fluid is boiled away.	Care should be taken that the heater junction box is sealed properly and that excessive moisture is prevented from entering. Periodic inspection of the junction box and thermal well assembly should be considered in unusually wet installations and solutions operating above 180 degrees F. If solution is found in the Thermowell, a pressure test should be preformed to verify integrity. Periodic inspection and possible relocation of the heater to a more protected location can reduce the potential of future problems.
8) Guard material cracking at weld seams or solution interface.
CAUSE	SOLUTION
Check solution for temperature and chemical compatibility with polypropylene.	Switch to fluoropolymer or CPVC guards as required.
9) Heaters tripping GFP/ELCB circuits.
CAUSE	SOLUTION
Usually caused by moisture trapped within the element insulation. Test insulation value with a meggar. Should measure a resistance of at least 50 megohms between the sheath and element. (Preferably greater than 200 megohms @ 500 VDC).	If lower than noted value, replace the heating element, as field repairs are impractical and temporary.
Defective GFP/ELCB circuit. Test by running a known good electrical load through the coil to verify operation.	Replace as required.
Low setting on GFP/ELCB circuit. Some ground fault devices have adjustable switch settings.	Make sure the units are set for a minimum 5 Ma trip point.
Moisture within the junction box or thermowells.	Remove heater cover and inspect epoxy surfaces, thermal protector and Thermowell for moisture or conductive plating salts. Clean/dry and remove any deposits. Apply RTV sealant to gaskets or threaded areas and return to service.
10) Fluoropolymer sheath on single element or phase of the heater melted.
CAUSE	SOLUTION
Usually caused by a combination of operation with low liquid level and one leg of the power source open (blown protector, open breaker or single phase wiring).	Replace heater and correct power/wiring problem.