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by Thomas Webster on Tue, May 25, 2021 @ 14:05 PM
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Buffer and barrier seal support plans are required for dual seals to operate. Dual mechanical seals have become more prevalent in pumping equipment to maintain higher safety and reliability standards and avoid environmental impact resulting from seal leakage. Managing an industrial fluid system’s flow is fundamental to maintaining optimal performance of rotating equipment, especially on critical seal support systems.
Managing the system’s flow becomes particularly critical when operating in cold weather. When buffer and barrier fluids are operating in cold temperatures, they can become more viscous and have a reduced flow rate. This can lead to the seal support system not providing proper lubrication and heat removal, resulting in mechanical seal failure.
Comparing Buffer Fluids and Barrier Fluids
In addition to process fluid, dual seals use an external fluid. This fluid is classified as either a buffer or a barrier fluid based on its arrangement. A buffer fluid plan is an unpressurized fluid system with a seal pot that is used to provide cooling or lubrication to fluids with unsatisfactory lubricating characteristics, such as light hydrocarbons. A barrier fluid plan is a pressurized fluid system with a seal pot. It is used when the process fluid needs to be isolated from the environment to prevent flashing, polymerization, or crystallization. A barrier fluid plan may also be used when the pumped fluid is toxic or hazardous. Barrier fluids are typically pressurized to 15-30 psi above the seal chamber pressure. It is critical to select the right buffer/barrier fluid to ensure an industrial fluid system’s flow, especially in cold weather applications.
Buffer and Barrier Seal Plans
Buffer and barrier fluids can be stored, delivered, and monitored through various methods, each identified by an API plan number. Below, examples of buffer and barrier seal plans are detailed.
|
API Plan |
Design |
Plan Description |
|
Plan 52: Buffer Fluid Seal Pot |
|
API Plan 52 utilizes a reservoir and circulates unpressurized buffer fluid between the inboard and outboard seals. This plan provides additional heat removal from the inboard seal when required and acts as a secondary seal to prevent process fluid from leaking into the environment. No pressurization is required for the reservoir. |
|
Plan 53A: Barrier Fluid Seal Pot Pressurized by Nitrogen |
|
API Plan 53A utilizes a reservoir and circulates pressurized barrier fluid between the inboard and outboard seals, where the barrier fluid is pressurized using a nitrogen source. This plan provides additional heat removal from the inboard seal when required and is used to prevent process fluid from leaking into the environment. As long as the reservoir pressure is maintained, the chance of process fluid leakage is low. |
|
Plan 53B: Barrier Fluid Pressurized by Bladder Accumulator |
|
API Plan 53B utilizes a reservoir and circulates pressurized barrier fluid between the inboard and outboard seals, where the barrier fluid is pressurized using a bladder accumulator. The use of a bladder accumulator achieves higher barrier fluid pressure. This plan provides additional heat removal from the inboard seal when required. The barrier fluid and nitrogen are separated by a bladder which effectively prevents nitrogen from mixing with the barrier fluid, as in the case of Plan 53A. |
|
Plan 53C: Barrier Fluid Pressurized by Piston Accumulator |
|
API Plan 53C utilizes a reservoir and circulates pressurized barrier fluid between the inboard and outboard seals, where the barrier fluid is pressurized using a piston accumulator. The piston accumulator dynamically adjusts the barrier pressure which is based on the seal chamber pressure; thus, a fixed, steady differential pressure is achieved across the inboard seal faces. This plan is used when seal chamber pressure can vary during pump operation and to prevent process fluid from leaking into the environment. This plan also provides additional heat removal from the inboard seal when required |
|
Plan 54: Barrier Fluid Pressurized by External System |
|
API Plan 54 is a custom engineered system that delivers a pressurized barrier fluid to the seal chamber. The barrier fluid is circulated to and from the seal chamber via a pump located on an external reservoir. The barrier fluid is maintained at a pressure greater than that of the seal chamber. This plan can contain coolers, filters, and other components based on parameters of a specific application. |
Choosing Buffer and Barrier Fluids to Maintain Industrial Fluid System’s Flow Efficiency
Common buffer and barrier fluids include water and glycol solutions, alcohols, kerosene and diesel fuels, lube oils, synthetic lube oils, and heat transfer fluids. For cold weather applications, buffer/barrier fluid pour point, viscosity, and pump temperature range should be taken into account with the goal of maintaining an industrial fluid system’s flow. The pour point of a liquid is the temperature below which the liquid loses its flow characteristics. Common buffer and barrier fluids and their properties are detailed in the chart below.
|
Family |
Fluid |
Kinematic Viscosity [cSt] |
Pour Point |
Pump Temperature Range [ºC] |
||
|
Water and Glycol Solutions |
|
at 40ºC |
at 100ºC |
|
Min |
Max |
|
Water |
0.68 |
0.29 |
0 |
5 |
70 |
|
|
Propylene Glycol |
2.6 |
0.7 |
-33 |
-29 |
77 |
|
|
Alcohols |
n-Propyl-Alcohol |
1.5 |
0.45 |
-126 |
-124 |
69 |
|
Kerosene and Diesel Fuels |
K-1 Kerosene |
1 |
n/a |
-29 |
-23 |
-21 |
|
K-2 Kerosene |
1.4 |
0.6 |
-34 |
-29 |
132 |
|
|
D-1 Diesel |
1.4 |
0.6 |
-34 |
-29 |
149 |
|
|
D-2 Diesel |
2.7 |
1.0 |
-59 |
-12 |
82 |
|
|
Lube Oils |
Lube-1 |
13.9 |
5.1 |
-59 |
-29 |
76 |
|
Lube-2 |
9.5 |
2.6 |
-12 |
-7 |
140 |
|
|
Lube-3 |
9.5 |
2.3 |
-50 |
-7 |
135 |
|
|
Synthetic Lube Oils |
Synth-1 |
7 |
1.5 |
-62 |
-32 |
221 |
|
Synth-2 |
22 |
3.3 |
62 |
-4 |
227 |
|
|
Synth-3 |
37.2 |
5.35 |
-50 |
17 |
227 |
|
|
Heat Transfer Fluids |
Aromatic-1 |
29 |
4 |
-4 |
13 |
316 |
Water would be an unacceptable buffer/barrier fluid for cold weather applications due to its low pour point; however, water can be mixed with propyl alcohol to lower the freezing temperature of the buffer/barrier fluid. Most oils and alcohols are less likely to freeze and have low pour points, offering strong benefits for cold weather applications. However, choosing a buffer/barrier fluid depends on much more than environmental temperature and fluid system experts should be consulted. Buffer/barrier fluids should also:
- Have good lubricity
- Be compatible with process fluid
- Have good heat transfer properties
- Be compatible with seal materials
- Not form deposits on seal faces
- Remain stable at ambient temperatures
- Be safe to use, handle, and store
Maintaining Buffer and Barrier Fluids
After selecting a seal plan and buffer/barrier fluid, the fluid and sealing environment should be properly maintained to ensure peak performance. This includes routine checks for changes in pH, viscosity, color, consistency, and the presence of solids. Buffer and barrier fluids should be changed on a regular basis depending on the fluid at hand and the process fluid characteristics.
Buffer and barrier fluids are typically cooled to assist with heat removal. Depending on local temperatures, these fluids may need to be cooled in the summer. Local seal support experts will be able to recommend the appropriate method to maintain buffer and barrier fluids based on specific process requirements as well as environmental conditions.
Selecting the Right Seal Plan and Buffer/Barrier Fluid
If your current buffer/barrier seal support plans are underperforming, or you are looking for the most effective buffer/barrier fluid to support dual mechanical seals in the event of cold weather, Swagelok Edmonton will work with you to understand your needs and recommend solutions.
Our highly experienced Field Advisors will perform an onsite analysis of your pumping process and recommend the right buffer/barrier seal support plan, buffer/barrier fluid that will work best for your use case and operating environment. Edmonton Valve & Fitting is familiar with cold weather seal support challenges in Central and Northeast Alberta and is readily available to help improve your industrial fluid system’s flow.
Edmonton Valve & Fitting can also recommend additional solutions for cold weather applications, such as Pre-Insulated Traced Tubing Bundles. These bundles provide reliable process temperature maintenance in a variety of analytical and process instrument applications, including impulse lines, sample lines, and process lines.