SUBJECT : Troubleshooting mechanical seals at equipment disassembly 3-9

All seals fail for the same reasons:

After the failure has occurred you'll frequently get a chance to analyze the failed components. You're going to be looking for several things:

In the following paragraphs we'll be inspecting the individual components and looking for evidence of the above.

THE CARBON FACE

Chipping on the O.D. of the carbon. Indicating vibration.

Pits in the carbon face. This problem is often associated with poor grades of carbon/ graphite.

Chips at the I.D. of the carbon

Phonograph finish on the carbon face.

Chemical attack of the carbon.

Cracked or damaged carbon face.

A coating is forming on the carbon face:

Coking

Shiny spots, cracks and raised portions of carbon.

Excessive carbon wear in a short period of time. Evidence of excessive heat is usually present.

The carbon has a concave or convex wear pattern

The carbon is not flat.

THE HARD FACE.

Chemical attack.

Cracked or broken.

Heat check (a common problem with coated or plated faces)

Hard coating coming off of the face.

Analysis of the wear track on the hard face.

Deep grooves&emdash;excessive wear. Solids imbedded in the carbon are causing the problem. The solids were trapped between the faces when the seal faces opened.

The wear track is wider than the carbon.

The wear track is narrower than the carbon.

Non Concentric pattern. The wear track is not in the center of the hard face.

Uneven face wear. The hard face is distorted:

The product is sticking to the seal face. The product is changing state and becoming a solid. Most products solidify for the following reasons:

The hard face is not flat.

THE ELASTOMER.

Compression set. The O-ring has changed shape.

Shrinking, hardening or cracking.

Torn nibbled, or extruded.

Swelling, changing color, weight or size. Almost always caused by:

Torn rubber bellows.

THE METAL CASE OR BODY OF THE SEAL.

Corrosion.

Rubbing--All around the metal body.

Partial rubbing -- On the metal body.

Discoloration. Caused by high heat. Stainless steel changes color at various temperatures.

FAHRENHEIT
COLOR OF THE METAL
CENTIGRADE
700 - 800
Straw Yellow
370 - 425
900 - 1000
Brown
480 - 540
1100 - 1200
Blue
600 -650
> 1200
Black
> 650

NOTE: To tell the difference between discoloration caused high heat and product attaching to the metal part, try to erase the color with a common pencil eraser. Discoloration will not erase off.

Product sticking to the metal surfaces.

The following applications cause a vacuum to be present in the pump stuffing box.

The Teflon coating is coming off some of the metal parts.

DRIVE LUGS, PINS, SLOTS, etc.

Broken.

Wear on one side of the drive lug or slot.

The drive pins are falling out of the holder.

THE SPRINGS.

Broken or cracked.

Corroded.

Clogged.

Twisted.

The drive lugs or slots are worn on both sides.

Broken Metal Bellows.

Because these seals do not have a dynamic elastomer to provide vibration damping some other means must be provided or vibration will always be a problem.

THE SLEEVE, OR SHAFT.

Grooves or pits at the seal dynamic elastomer location.

Rubbing at the wear ring location.

Corrosion. See above description under metal corrosion

.THE SET SCREWS.

THE GLAND.

Rubbing at the I.D.

Corrosion.

Passages clogged or not connected properly.

BUSHINGS

Rubbing at the I. D.

Erosion.

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