METAL HEATERS

Cause

Chemical Corrosion (chemical incompatibility). Usually characterized by 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 coil sheath (usually most severe in the heated inlet tube areas).

Solution

Check chemistry or MSDS sheets and replace with appropriate coil material.

Cause

Galvanic corrosion. Usually caused by dissimilar metals between tank and coil sheath. (For example, a T304 stainless coil used in a T316 stainless tank may cause corrosion on the T304 stainless material as the less noble metal on the electromotive chart [T304 stainless] will become anodic and corrode to the cathodic [T316 stainless] metal). Corrosion of this type may be seen as a general etching or pitting along the side of the coil facing the more noble metal (sometimes seen in oval patterns). In the case of a coil 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.

Solution

Replace coil/tank to match materials, or isolate different materials.

Cause

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. (Oxygen is necessary to form the corrosion resistant oxide layer on metals).

Solution

Coils should either be cleaned frequently to prevent this type of corrosion or replaced with a material less prone to this type of attack.

Cause

Tube etched or has porous appearance on outside surface (titanium coils). Usually caused by operation with a cathodic charge applied to the coil in a normally compatible application.

Solution

Check with chemical supplier to verify proper sheath material selection. Install isolators to inlet/outlet and protect coil from contact with charged parts.

Cause

Tube etched or has porous appearance on the inside of the tube. Usually caused by carbonic acid formation in condensate water due to excessive air in system.

Solution

Install steam trap type that is capable of venting all air from system, install bypass vent or replace exchanger with a type compatible with the level of evolved carbonic acid.

Cause

Contact with electrically charged work. Contact of any metal coil 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 coil.

Solution

Locate coil in the tank to avoid contact with charged work or protect the coil from contact with a non- conductive guard material, or install coil with isolator couplings to isolate them from piping.

Cause

Weld failures at cross tubes or splices caused by chemical incompatibility and galvanic corrosion on welds.

Solution

Contact chemical supplier or coil manufacturer for alternate materials of construction.

Cause

Split coil sheath (Metal coils). Caused by severe chemical attack and thinning of tubing.

Solution

Replace coil with appropriate sheath material as required. Consult with chemical supplier for material recommendation.

Cause

Metal plate-out on coil surface. Inspect for contact between the coil sheath and plating tank cathode, work or parts accumulation on tank bottom contacting the coil sheath. May also be caused by a difference in potential between the coil supply piping and the rectifier ground.

Solution

Either isolate the coil or connect the coil and rectifier ground wire to the same verified ground source.

Cause

Stray voltage/current from other sources entering tank through coil sheath. Ground. Test coil to ground for voltage/current flow to verify presence of flow.

Solution

Locate source of voltage/current flow and correct condition. Dielectric insulators can be added to the plumbing connections to disrupt flow.

Cause

Inlet/outlet tube corroded at solution interface.

Solution

Replace affected area with heavier gauge material and cover/coat interface area with chemically compatible heat shrink tubing or coating.

Cause

Inlet tube/header corroded from accelerated chemical attack on hottest portion of coil.

Solution

Chemical incompatibility, contact chemical supplier or coil manufacturer for alternate materials of construction.

Cause

Physical damage to coils. Coils should be inspected for any physical damage prior to installation and during routine cleaning and maintenance.

Solution

Shipping damages must be reported to both the factory as well as the carrier. Isolate coils with guards or position in a safe location in the tank to minimize the potential for physical damage from racks and parts entering and exiting the tank. Damage caused by improper cleaning can result in dangerous operation conditions. Do not operate damaged coils.

Cause

Collapsed or twisted inlet/outlet tubes caused by insufficient support of inlet/outlet pipe nipple during installation.

Solution

Repair/replace damaged components and support inlet/outlet nipple during installation.

Cause

Collapsed or twisted inlet/outlet tubes: coils not supported on adjacent end allowing weight or buoyancy of coil to distort/damage tubing.

Solution

Repair coil and reinstall with appropriate hangers or anti-floatation weights.

Cause

Collapsed or twisted inlet/outlet tubes: Header/piping thermal expansion damage to tubing.

Solution

Repair/replace damaged components and install pipe elbows at coil connections to allow for expansion.

Cause

Installation problems. Coils should be handled carefully and must be fully supported during installation. Using only the metal riser as a handle during installation will cause damage to the welds.

Solution

Support both ends of coil during installation and service. Large coils should be installed with support hangers.

Cause

End caps of exchanger broken off or cracked from water hammer.

Solution

Install a condensate drip trap ahead of steam valve to reduce accumulation of condensate and a water hammer arrester in plumbing to reduce water/steam hammer.

Cause

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.

Solution

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

Cause

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.

Solution

Consult factory for possible repair. Do not operate damaged heater. Replace or discard as required.

Cause

Usually caused by pressurized discharge of heater contents due to a corrosion of the sheath and vaporization of fluid that entered the element.

Solution

Turn off power and remove the heater from service immediately as dangerous operating conditions may occur. Check application for compatibility before replacing heater.

Cause

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.

Solution

Do not operate damaged heaters. Heaters should either be returned to factory for repair or be discarded.

Cause

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

Solution

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.

Cause

Usually caused by a difference in potential between the heater ground connection and that of a DC power supply (rectifier).

Solution

Test heater for permanent damage and repair/replace as required. Connect heater ground wire and rectifier ground to the same, verified ground source.

Cause

Usually caused by moisture trapped within the element insulation.

Solution

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.

Cause

Defective GFP/ELCB circuit.

Solution

Test by running a known good electrical load through the coil to verify operation. Replace as required

Cause

Low setting on GFP/ELCB circuit.

Solution

Some ground fault devices have adjustable switch settings. Make sure these units are set for a minimum 5 Ma trip point.

Cause

Moisture within the junction box or thermal wells.

Solution

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.

Cause

Caused by chemical attack, saturation of insulation and hydraulic expansion of magnesium oxide insulation as it converts to magnesium hydroxide.

Solution

Replace heater with appropriate sheath material as required. Consult with chemical supplier for recommendation.

Cause

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.)

Solution

Check chemistry or MSDS sheets and replace with appropriate sheath material.

Cause

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.

Solution

Replace heater or tank to match materials. Tank can also be lined with a non-conductive material to isolate heater.

Cause

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.)

Solution

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.

Cause

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.

Solution

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.

Cause

Overheating. Heater operated out of solution or used without the thermal protector or used in a viscous solution.

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.

Cause

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.

Solution

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.

Cause

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.

Solution

Locate heater in the tank to avoid contact with charged work or protect the heaters from contact with a non- conductive guard material.

Cause

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.

Solution

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.