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Learning

MECHANICAL

SEAL TROUBLESHOOTING

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Learning

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Learning MECHANICAL SEAL FAILURE

BLISTERING OF SEAL FACES

SEAL FACE BLISTER - CARBON SEAL FACE BLISTER - SILICON CARBIDE

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Learning MECHANICAL SEAL FAILURE

CAUSES:

Using carbon seal faces in oil (all types) Exceeding the limits of the material Flashing

FAILURE MODES:

Seal face incompatibility Exceeded limits (speed, temperature, pressure) Misapplication

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Learning MECHANICAL SEAL FAILURE

SOLUTIONS:

Use SC/TC face combination in oils Operate within seal limits Insure seal face lubrication

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Learning MECHANICAL SEAL FAILURE

WEAR TRACK WIDER THAN NARROW SEAL FACE

  

                                                          

ROTARY SEAL FACE - WIDE TRACK STATIONARY SEAL FACE - NARROW

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Learning MECHANICAL SEAL FAILURE

CAUSES: Improper centering of stationary type seal Radial shaft run-out (bearing problem) Shaft deflection/wobble during operation

FAILURE MODES: Improper installation Equipment conditions Equipment design

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Learning MECHANICAL SEAL FAILURE

SOLUTIONS: Check bearings for radial run-out exceeding limit of seal

type Review installation techniques/instructions Calculate L/D ratio for equipment - Upgrade if

necessary

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Learning MECHANICAL SEAL FAILURE

CENTERED OR MISCENTERED

STATIONARY (TYPE SEAL) - CENTERED ROTARY (TYPE SEAL) - MISCENTERED

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Learning MECHANICAL SEAL FAILURE

CAUSES: Centered seal face wear track indicates - Properly centered seal and good equipment operation

improper centered seal face wear track indicates - Improper centered seal (rotary type) during installation Equipment condition - Radial runout Equipment operation - Off curve, vibration

FAILURE MODES: Improper installation Equipment conditions

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Learning MECHANICAL SEAL FAILURE

SOLUTIONS: Check bearings for radial run-out exceeding limit of seal

type Review installation techniques/instructions Check equipment for shaft - Seal chamber concentricity

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Learning MECHANICAL SEAL FAILURE

EVEN / UNEVEN WEAR TRACK

EVEN WEAR TRACK UNEVEN WEAR TRACK

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Learning MECHANICAL SEAL FAILURE

CAUSES:

Even wear on a seal face usually indicates - Good contact between the mating seal rings

Uneven wear on a seal face indicates - Distortion of the seal ring due to over tightening, clamping,

or excessive pressure Distortion due to insufficient gland support Misaligned seal rings in a split seal Improperly stress relieved component

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Learning

MECHANICAL SEAL FAILURE

FAILURE MODES:

Improper installation Quality/design related issue

SOLUTIONS:

Review installation techniques/instructions Check/reduce torque and evenly tighten gland bolts Review operating conditions Reduce torque and evenly tighten gland bolts

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Learning MECHANICAL SEAL FAILURE

SCORING OR EROSION

SEAL FACE SCORING SEAL FACE EROSION

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Learning MECHANICAL SEAL FAILURE

CAUSES:

Rebuilding seal in dirty environment Faces opening/flashing/vibration/distortion of the seal face

due to temperature and pressure Minerals found in the fluid film between the seal faces

FAILURE MODES:

Abrasive particles between the seal faces Lack of seal face lubrication

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Learning MECHANICAL SEAL FAILURE

SOLUTIONS:

Maintain seal face flatness Eliminate dry running, flashing and vibration Use clean flush source with bushing Use suction re-circulation control Use harder seal face materials

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Learning

MECHANICAL SEAL FAILURE

CHIPPING ON OUTSIDE / INSIDE DIAMETER

SEAL FACE - CHIPPING O.D. SEAL FACE - CHIPPING I.D.

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Learning

MECHANICAL SEAL FAILURE

CAUSES:

Faces opening/flashing - Operating near vapor point Vibration Cavitation - Equipment operation Products hardening and setting-up Over pressurization

FAILURE MODES:

Inadequate environmental controls Misapplication

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Learning

MECHANICAL SEAL FAILURE

FAILURE MODES: Product harden, set-up Exceed limits (speed, temperature, pressure) Equipment operation Lack of seal face lubrication

SOLUTIONS: Proper environmental controls Check equipment operating conditions Insure the product is not flashing between the seal faces Seal operating within design parameters

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Learning MECHANICAL SEAL FAILURE

COKING OR CRYSTALLIZED PRODUCT

SEAL FACE - COKING SEAL FACE - CRYSTALLIZED

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Learning MECHANICAL SEAL FAILURE

SYMPTOMS: Coking or crystallized product

CAUSES: Excessive temperatures (both) Dirty or contaminated fluid (coking) Operating outside of the temperature envelope of the

fluid (both) Small clearances in the seal chamber Pump cooling jacket not efficient Fluid evaporation between the seal faces (crystallization)

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Learning

MECHANICAL SEAL FAILURE

FAILURE MODES:

Inadequate environmental controls Product harden, set-up or coked Exceeded limits (speed, temperature, pressure)

SOLUTIONS:

Proper use of environmental controls Operate within seal limits Understand the temperature envelope of the fluid being

sealed

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Learning MECHANICAL SEAL FAILURE

HEAT CRACKING

SEAL FACE - HEAT CRACKING SEAL FACE - HEAT CRACKING

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Learning MECHANICAL SEAL FAILURE

CAUSES:

Exceeded PV limits of seal face materials Dry running Excessive heat from product

FAILURE MODES:

Lack of seal face lubrication Exceeded limits (speed, temperature, pressure) Inadequate environmental controls

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Learning MECHANICAL SEAL FAILURE

SOLUTIONS:

Operate within seal limits Eliminate dry running conditions Proper use of environmental controls

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Learning STUFFING BOX PRESSURE

Seal chamber pressure must be known before the proper seal and flush plan can be selected.

Seal chamber pressure can vary from pump design, flow rate, and fluid being pumped. Suction and discharge pressures are required to perform these calculations.

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Learning

STUFFING BOX PRESSURE

Often, pump spec sheets can be old and outdated e.i., design, operating points may have changed due to a change in process demands. It is for this reason, that suction and discharge pressures should be physically measured with pressure gauges.

                                                            

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Learning STUFFING BOX PRESSURE

The following equations are based on closed throat design seal chambers. Pump designs include wear rings and balance holes in the impeller to reduce thrust load on the bearings. The seal chamber pressure is a function of wear ring clearance as well as size and location of the balance holes.

Quick Estimate Psb = Ps + .25(Pd-Ps)

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Learning STUFFING BOX PRESSURE

Enclosed or Semi-Enclosed Impellers with wear ring design and balance holes

Psb = Ps + .05(Pd-Ps)

Open impeller design with ANSI Pump-Out vanes or Repeller (no balance holes)

Psb = Ps + *D(Pd-Ps)

*D = .3 if the impeller is at minimum diameter and .1 if the impeller is at maximum diameter.

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Learning STUFFING BOX PRESSURE

Single Stage, Double Suction Pumps

The single stage, double suction impeller is placed between bearings while the seal chambers are located adjacent to the suction eyes of the impeller.

The stuffing box pressure is equal to the suction pressure.

Psb = Ps

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Learning STUFFING BOX PRESSURE

Two Stage Horizontal Pumps Impeller arrangement can have two configurations:

1) Back to BackIn this arrangement, the seal chambers are located adjacent to the suction eye of the impeller. One chamber will see suction pressure and the other will see first stage discharge pressure.

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Learning

STUFFING BOX PRESSURE

2) Eye to Eye

In this arrangement the seal chambers are located adjacent to the backside of the impeller.

One chamber will see the discharge of the first stage and the other will see pump discharge pressure (second stage discharge).

Psb1 = Ps + .5(Pd-Ps)

Psb2 = Pd

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Learning STUFFING BOX PRESSURE

Multi-Stage Horizontal Pumps

Multi-stage Boiler Feed Pumps are used to develop high pressures, but the seal chamber is not necessarily at a high pressure. These pumps have a low pressure chamber (suction pressure) and a higher-pressure chamber (pressure between suction and discharge).

Typically, a balance line is used to reduce pressure in the higher pressure seal chamber. Provided pump tolerances are in check, the higher-pressure seal chamber is as follows:

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Learning

STUFFING BOX PRESSURE

Note: If pump tolerances are not in check, and in the absence of a balance line the higher-pressure chamber will be a pressure between suction and discharge pressure.

Psb1 = Ps

Psb2 = Ps+75 psig

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Learning STUFFING BOX PRESSURE

Mulit-Stage Vertical Pumps (Can or Turbine)

In these pumps the seal chamber is located at the discharge elbow. Therefore the seal chamber pressure would see discharge pressure.

Psb = Pd

Note: The installation of a bleed-off line can reduce seal chamber pressure provided pump tolerances are in check.

Psb = Ps+75