Metal Coils

1) Holes on the surface.
CAUSE	SOLUTION
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).	Check chemistry or MSDS sheets and replace with appropriate coil material.
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.	Replace coil/tank to match materials, or isolate different materials.
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).	Coils should either be cleaned frequently to prevent this type of corrosion or replaced with a material less prone to this type of attack.
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.	Check with chemical supplier to verify proper sheath material selection. Install isolators to inlet/outlet and protect coil from contact with charged parts.
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.	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.
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.	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.
Weld failures at cross tubes or splices caused by chemical incompatibility and galvanic corrosion on welds.	Contact chemical supplier or coil manufacturer for alternate materials of construction.
Split coil sheath (Metal coils). Caused by severe chemical attack and thinning of tubing.	Replace coil with appropriate sheath material as required. Consult with chemical supplier for material recommendation.
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.	Either isolate the coil or connect the coil and rectifier ground wire to the same verified ground source.
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.	Locate source of voltage/current flow and correct condition. Dielectric insulators can be added to the plumbing connections to disrupt flow.
Inlet/outlet tube corroded at solution interface.	Replace affected area with heavier gauge material and cover/coat interface area with chemically compatible heat shrink tubing or coating.
Inlet tube/header corroded from accelerated chemical attack on hottest portion of coil.	Chemical incompatibility, contact chemical supplier or coil manufacturer for alternate materials of construction.
Physical damage to coils. Coils 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. 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.
Collapsed or twisted inlet/outlet tubes caused by insufficient support of inlet/outlet pipe nipple during installation.	Repair/replace damaged components and support inlet/outlet nipple during installation.
Collapsed or twisted inlet/outlet tubes: coils not supported on adjacent end allowing weight or buoyancy of coil to distort/damage tubing.	Repair coil and reinstall with appropriate hangers or anti-floatation weights.
Collapsed or twisted inlet/outlet tubes: Header/piping thermal expansion damage to tubing.	Repair/replace damaged components and install pipe elbows at coil connections to allow for expansion.
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.	Support both ends of coil during installation and service. Large coils should be installed with support hangers.
End caps of exchanger broken off or cracked from water hammer.	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.