Seal Face Wear Patterns

Guide to Mechanical Seal Types and Component Properties - Page 8

Certain wear patterns on your seal face may indicate problems that require attention. This section is meant to be a guideline to help you stave off unnecessary seal repairs due to a shaft or pump problem or due to environmental considerations.

The examples here will provide you with indicators only. A thorough, professional inspection will ascertain and confirm any existing problems more accurately and a professional seal engineer will be able to make appropriate recommendations.

NE Seal recommends always examining your seal faces when changing a seal. This way you can be alerted to conditions which may rapidly damage the replacement seal and incur unnecessary maintenance costs. If in doubt, please call us and we will render a professional opinion.

	Proper Wear Pattern The wear pattern on the wide face will be equal to the width of the narrow face. When this occurs, the cause of leakage is unlikely to have been 'face related'. The wear pattern should be concentric with the outer and inner diameters.
	Narrow Wear Pattern A wear pattern that is thinner than the narrow face. When this pattern is present, it indicates that the thin face was distorted by pressure causing an inadequate film between the faces. To cure this symptom, either reduce the pressure or change the seal design to a higher pressure rated seal.
	Wide Wear Pattern A wear pattern that is wider than the narrow face indicates that opening of the faces created excessive film between the faces. This can be caused by a cocked stationary face, pump misalignment, pipe strain or pump cavitation. The pump misalignment or vibration can cause the rotary face to move back and this face may remain open due to secondary seal 'hang-up' on the shaft. The most practical solution to this problem is realignment of the pump. Where realignment is not possible, an assembly with a static secondary seal may reduce face 'hang-up'. A wide wear pattern is also symptomatic of excessive shaft motion.
	No Wear Pattern A situation where the rotary face is not turning against the stationary face. Possible causes are slipping of the rotary drive mechanism and interference of the rotary with the stuffing box or gland, or improper installation.
	Intermittent Wear Pattern A wear pattern that only touches the wide face intermittently. The cause of this symptom can be unflat faces, distortion of the stationary face by clamping against an uneven stuffing box face, unevenly tightening gland bolts, or cocking of the stationary face. The remedey is to make certain that the stuffing box face is even, that the gland is evenly tightened and the seal assembly faces are flat when placed in service. Flexible mounted stationary rings can help this condition.
	Uneven Wear Pattern An uneven wear pattern that rotates off the entire wide face at two points. The second illustraction shows a round wear pattern that rotates on the entire face. The cause on both is due to pump shaft / drive motor misalignment. The cure is to realign the motor, the pump or the pump shaft. This generally means the gland was not properly shimmed and the stationary unit was riding near the shaft at one location. This may not hurt the life of the seal.
	Cracked Hard Face There are two causes for cracked seal faces. In ceramic, thermal shock can cause cracking. This is likely to occur when rapid changes in temperature are present. The second cause of cracking is mechanical shock. This is likely to occur when the face is hit or dropped or is distorted by the gland bolt load. The cures for these problems are cautious handling and improving the thermal capacity of the face materials.
	Chipped Edges The cause of the chipping is separation of the faces and subsequent breakage when they slam back into each other again. This is common with fluids that change from a liquid to a gas or when the pump experiences severe cavitation. Reduction of the face heat will cure vaporization through proper flushing. Cavitation is cured by proper liquid volume getting to the pump.
	Flaking and Peeling Stainless steel faces are usually plated with a hard facing of stellite, ceramic, tungsten carbide or a variety of other materials. Flaking or peeling is usually a sign of either a defective coating or chemical attack at the bond between the base metal and the plating material. The attack may be aggravated by the heat generation at the seal face. Switching to a solid face material should solve this problem.
	Pitting, Blistering & Corrosion Carbon face has been attacked by corrosion. Carbon faces are selected for a particular application and should not be subjected to this condition. If this occurs, the solution is to change the face material. A few fluids such as nitric acid, chlorosulphonic, oleum, and some exotic highly oxidizing acids will attack carbon or carbon graphite materials. This will also occur in carbons with excess porosity as liquids may solidify in these holes and expand causing miniature cratering and blistering.
	Deep Wear This condition often accompanies seals in abrasive service and seals in crystallizing products. The particles embed in the carbon face and grind away at the hard face. Remedies for this problem are controls that prevent crystallization such as adding heat, exclusion of abrasive product from the faces by protections methods such as flushing.
	Heat Checking The hard face has been heat checked, because the seal face is unable conduct heat away. The heat generation can come from the product temperature, friction, or intermittent vaporization of the product (including resulting friction and heat) coupled with brief cooling of the faces from liquid product. The cures for heat checking are reducing temperature by flushing or cooling the faces, changing materials or changing the face design.