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Equipment Overview | Filter Pump Industries / Penguin Pump | Process Technology


Metal Heaters

1) Holes in heater sheath (Metal Heaters)
Corrosion. (Chemical incompatibility) Usually either general etching along entire heated length, weld seam or solution interface areas. May also be seen as small irregular pits, patchy discoloration or cracks along the heater sheath. (Usually most severe in the heated areas.) Check chemistry or MSDS sheets and replace with appropriate sheath material.
Galvanic corrosion. Usually caused by dissimilar metals used during heater construction or between tank and heater sheath. (For example, a T304 S/S heater used in a T 316 S/S tank may cause corrosion on the T304 S/S material as the less noble metal on the electromotive chart [T304 S/S] will become anodic and corrode to the cathodic [T316 S/S] metal). Corrosion of this type may be seen as a general etching or pitting along the side of the heater facing the more noble metal (sometimes seen in oval patterns). In the case of a heater made with the same metal combinations, corrosion will typically start on the less noble metal, about 1/4" back from their junction. Usually, the relationship of more surface area of the noble metal will cause increased corrosion on the lesser surface area of the less noble metal. Replace heater or tank to match materials. Tank can also be lined with a non-conductive material to isolate heater.
Oxygen deprivation corrosion. Can be seen as pits or cracks under areas of buildup or in areas where metal parts overlap and prevent contact with oxygenated solution. (This oxygen is necessary to form the corrosion resistant oxide layer on metals.) Heaters should either be cleaned frequently to prevent this type of corrosion or replaced with a material and construction less prone to this type of attack.
Buildup. Any deposits on the heater sheath will insulate the element causing excessive internal temperatures. Darkened carbonized deposits and scorching are usually evident on heated portions of sheath. Element failure may result in arcing of the melting resistance wire to ground and will manifest itself as a series of longitudinal holes through the sheath along the hot zone. Clean heaters frequently in solutions that buildup on the heater sheath or consider de-rating replacement heaters to reduce surface temperatures and the buildup rate. 
Overheating. Heater operated out of solution or used without the thermal protector or used in a viscous solution. Blue/black or golden discoloration over the hot zone of the element. Element may even arc to the sheath in a series of longitudinal holes. Verify that the correct watt density heater has been selected. Heater thermal protectors should be checked for correct wiring. Install liquid level controls and replace heater as required.
Holes around and above bumper/standoff (metal over the side heaters). Usually due to chemical attack on sheath, saturated element insulation and arcing to the sheath. Check compatibility of solution. Examine element for pitting behind protector thermal well caused by oxygen deprivation corrosion. Replace heater with appropriate sheath material as required. 
Contact with electrically charged work. Contact of any metal heater with DC power within the plating tank will cause a discharge to the sheath, resulting in any of the following conditions: arc type hole through the sheath, increased corrosion in the area of contact or excessive buildup/plate-out depending on the polarity of the DC power in contact with the heater. Locate heater in the tank to avoid contact with charged work or protect the heaters from contact with a non- conductive guard material.
Holes in the Protector thermowell. Usually caused by moisture or fluids entering the junction box and migrating down the thermal well tube. Over time, this liquid will degrade the protector encapsulation and provide a current path and subsequent arcing to the metal thermal well. Replace heater or thermowell assembly as required. Make sure that the junction box is sealed and heater is not operated under the cover of a tank. 
2) Swelled or split heater sheath (Metal Heaters).
Caused by chemical attack, saturation of insulation and hydraulic expansion of magnesium oxide insulation as it converts to magnesium hydroxide.  Replace heater with appropriate sheath material as required. Consult with chemical supplier for recommendation. 
3) Heaters tripping GFP/ELCB circuits.
Usually caused by moisture trapped within the element insulation. Test insulation value with a meggar. Should measure a resistance of at least 50 megohms @ 500 VDC between the sheath and element. (Preferably greater than 200 megohms.) Replace heater if insulation value is less than noted above.
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 these units are set for a minimum 5 Ma trip point.
Moisture within the junction box or thermal wells. Remove heater cover and inspect epoxy surface, thermal protector and thermal well for moisture or conductive plating salts. Clean/dry any deposits. Apply RTV sealant to gaskets or threaded areas and return to service.
4) Melted or overheated ground wires.
Usually caused by a difference in potential between the heater ground connection and that of a DC power supply (rectifier). Test heater for permanent damage and repair/replace as required. Connect heater ground wire and rectifier ground to the same, verified ground source.
5) Metal plate-out on heater sheath.  
Usually caused by either a difference in potential between the heater ground connection and that of a DC power supply (rectifier) or contact with charged components within the tank Inspect for contact between the heater sheath and plating tank cathode, work or parts accumulation on tank bottom contacting the heater sheath. Isolate components as required. If caused by a difference in potential between the heater ground and the rectifier ground, connect the heater ground wire and rectifier ground wire to the same verified ground source.
6) Physical damage to heaters. 
Heaters should be inspected for any physical damage prior to installation and during routine cleaning and maintenance. Shipping damages must be reported to both the factory as well as the carrier. Damage caused by improper cleaning can result in dangerous operation conditions. Do not operate damaged heaters. Heaters should either be returned to factory for repair or be discarded
7) Sand or magnesium oxide powder found in junction box.
Usually caused by pressurized discharge of heater contents due to a corrosion of the sheath and vaporization of fluid that entered the element. Turn off power and remove the heater from service immediately as dangerous operating conditions may occur. Check application for compatibility before replacing heater.
8) Installation problems.
Heaters should be handled carefully and must be fully supported during installation. Using the power supply wires, flexible riser or metal riser as a handle during installation will cause damage to the wiring and internal components. Consult factory for possible repair. Do not operate damaged heater. Replace or discard as required.
9) Discoloration/blackening of heater sheath; heater is distorted or misshapen.
Heater was energized while out of solution. A titanium heater will exhibit a rainbow discoloration to the hot zone sheath. A stainless steel heater will turn its hot zone to a dark brown color. Certain design heaters will distort their shape.
Ensure that the thermal protectors are properly wired to disable the heater when a high surface temperature is detected (when applicable). In addition, we recommend the use of a liquid level control is used to disable the heater when the liquid level drops to within 1-inch of the hot zone