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Your Mechanical Seal Leak Troubleshooting Guide for SAGD Operations

by Thomas Webster, on Thu, Jun 17, 2021 @ 08:06 AM

Mechanical seal leak troubleshooting can assist in identifying root causes of leaks in rotation equipment, such as centrifugal pumps

Mechanical seal leakage is typically unavoidable as seals age and develop wear. Inadequate flushing and lubrication of mechanical seals can also lead to seal damage, resulting in leaks that may present earlier in a seal’s life than anticipated. It is important to understand the common causes of leakage and how to remedy the issues in a timely manner to reduce downtime. The harsh process conditions and heavy, high viscosity process fluids involved in SAGD operations can often cause these issues to develop quicker than in operations involving lighter process fluids. 

Mechanical seal leakage causes can be categorized into five types:

  1. Heavy, high viscosity process fluids mixing with buffer/barrier fluids
  2. Improper selection of buffer/barrier fluids
  3. Changes in process conditions 
  4. Vibrations within rotating equipment
  5. Mechanical issues within the seal

Mechanical seal leakage can be minimized with high-quality seal flush systems, proper selection of buffer/barrier fluids for dual mechanical seals, and well-executed preventative maintenance plans. However, when mechanical seal leakage is present, each cause may require a different course of action to solve the problem. Let’s take a look into some of the common causes of leakage and suggestions for corrective action to implement when performing mechanical seal leak troubleshooting.

1) Leakage Due to High Viscosity Process Fluid Mixing with Buffer/Barrier Fluid

In operations with light, low viscosity process fluids, it is typically acceptable to have mixing occur between the process fluid and buffer/barrier fluid within dual mechanical seals. In such operations, the process fluid might even be used as the buffer/barrier fluid. 

However, SAGD operations pose a unique challenge due to the high viscosity of bitumen and crude oil. If mixing between a high viscosity process fluid and buffer/barrier fluid occurs, the seal is likely to become plugged, reducing or stopping the flow. This can cause the mechanical seal to overheat, resulting in leakage or even seal failure. Preventing such mixing can be accomplished through proper selection of buffer/barrier fluid. Some buffer/barrier fluids do not allow process fluid to diffuse into the seal fluid as readily.

2) Leakage Due to Improper Selection of Buffer/Barrier Fluid

In colder climates, it is critical to select the right buffer/barrier fluid for dual mechanical seals such that the seal is properly flushed and lubricated, even throughout cold winters. Considering the pour point of buffer/barrier fluids is crucial to maintaining proper lubrication. If a buffer/barrier fluid with a high pour point is selected, it will become very viscous in colder temperatures. This will likely result in reduced flow rates, causing the seal to overheat and leak or fail.

3) Leakage Due to Changes in Process Conditions

Mechanical seals and seal flush systems are specifically designed to support a particular set of process conditions, such as the process fluid itself, flow rate, pressure, and temperature. While process conditions typically change over time, this can have a negative impact on mechanical seals and can lead to leakage. If process conditions exceed the design specifications of either the mechanical seal or its seal flush system, leakage may occur as a result. Below, we detail possible changes in process conditions, how these changes can lead to mechanical seal leakage, and potential solutions.

Change in Process Condition

Associated Causes of Leakage

Potential Solutions

Increased Temperature

  • Distortion of seal faces
  • Insufficient cooling due to inadequate buffer/barrier fluid flow
  • Degradation of secondary seals
  • Replace the mechanical seal with a seal material graded for high temperatures
  • Remove/clear scaling from heat exchanger
  • Implement a heat exchanger with a higher capacity

Increased Pressure

  • Buffer fluid and/or seal faces are unable to accommodate higher pressure
  • Replace the mechanical seal with one designed for high-pressure applications or select a different buffer fluid

Elevated Amounts of Particulate

  • Decreased lubricity causing seal face abrasion
  • Utilize a cyclone separator to sufficiently remove particulates
  • Replace mechanical seal with one made of a more resilient material

Elevated Corrosive Concentrations in Process Fluid

  • Corrosion on seal faces, including pitting or crevices
  • Replace mechanical seal or upgrade to a seal with corrosion-resistant material


4) Leakage Due to Vibrations

Vibration occurring throughout pumping equipment can lead to mechanical seal leakage or failure. Sources of vibration leading to leakage include:

  • Misalignment of impeller shaft, motor shaft, or coupling
  • Loose pump and/or motor anchor bolts
  • Improperly functioning bearings

To prevent vibration issues that may lead to seal leakage or failure, a strong and detailed maintenance plan should be put in place for all rotating equipment. This will allow for early identification of root causes to remedy the issue before a leak presents.

5) Leakage Due to Mechanical Issues

Mechanical issues—such as mechanical distortion or damage, thermal distortion or distress, and misalignment—often involve different leak characteristics, which can help narrow down potential causes during mechanical seal leak troubleshooting. Let’s take a look into common mechanical issues, their associated leakage symptoms, and potential solutions.

  ⬤ Mechanical Distortion or Damage   Thermal Distortion or Distress  
  ⬤ Misalignment

Mechanical Issue

Symptom

Potential Solutions

Nicked or Scratched Secondary Seal Surfaces

  • Steady drip/leak from mechanical seal when shaft is either rotating or stationary
  • Assess secondary seal faces for nicks, scratches, burrs, and damage
  • If this is the case, replace secondary seal

Damaged or Porous Secondary Seal Surface

Mechanical Distortion/Faces Not Flat

  • Steady drip/leak from mechanical seal when shaft is either rotating or stationary
  • Assess whether or not seal faces are flat and are flush with one another, as well as whether or not parts holding the mating ring in place are square
  • If this is the case, realign seal faces and components

Thermal Distortion of Seal Faces

  • Steady leak from mechanical seal when shaft is rotating, but not when shaft is stationary
  • Increase cooling to the seal to prevent further thermal distortion
  • If the degree of distortion is too large, replace the seal

Thermal Distress on Seal Faces: liquid may be vapourizing at seal interface, seal faces may be overloaded, or seal faces may be receiving insufficient flushing from seal flush system

  • Steady leak from mechanical seal when shaft is either rotating or stationary
  • There may also be a sound from flashing or face popping
  • Assess seal chamber to determine whether or not there is a sufficient vapour pressure margin
  • Replace seal if needed and either increase flush flow rate from seal flush system or consider upgrading seal flush system

Misalignment of Mating Ring: mating ring is not square with the shaft

  • Steady leak from mechanical seal when shaft is rotating, but not when shaft is stationary
  • Assess shaft for proper alignment
  • If the shaft and mating ring are misaligned, realign them


The Best Method for Mechanical Seal Leak Troubleshooting

When performing mechanical seal leak troubleshooting, you will often find that the root cause is inadequate flushing from the seal flush system. While it is important to implement the correct mechanical seal and proper materials of construction to handle harsh conditions involved in SAGD operations, it is equally important to have a high-quality seal flush system in place. Insufficient cooling or insufficient flushing of contaminants on seal faces can often result in damage and distortion which can ultimately lead to mechanical seal leakage or even failure. As previously mentioned, this can become especially problematic in colder climates as buffer/barrier fluids are likely to have an increased viscosity and decreased flow rate.

Proper seal flush systems and rotating equipment maintenance can minimize leakage and reduce the need to perform mechanical seal leak troubleshooting

There are numerous reasons why a mechanical seal might experience leakage and oftentimes, the cause of leakage stems from multiple factors. The best resource for mechanical seal leak troubleshooting is local fluid systems experts who are highly experienced in local SAGD challenges and are knowledgeable on how to determine the correct seal flush system to optimize rotating equipment reliability. Field Advisors at Edmonton Valve & Fitting can perform an onsite consultation of your process to determine the root cause of leakage and recommend solutions that minimize downtime.

To find out more about how Edmonton Valve & Fitting can help with mechanical seal leak troubleshooting, contact us through our website or by calling 780-437-0640.
Topics:Sample Systems

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