api mechanical seal free sample

In one of the three previous parts this series of articles has dealt with the cost to reheat and/or evaporate flush injection from API Plan 32. It has also addressed industry technology that can be deployed to make seal flush piping plans more energy efficient while at the same time improving the reliability of the sealing device in the rotating equipment. Improvements and savings accrue from the application of best practice alternatives to API Piping Plans 32 and 54. The use of a modified API Plan 53A in the form of a Water Management System was described in Part 3; it eliminates the need to reheat and evaporate diluents. Available benchmark data prove the reliability benefits of this approach.

In the last of this series of articles, Part 4 now addresses the pumps used in condensate services. During many surveys the auditor will note pumps that are leaking hot condensate—a condition very often found in the paper industry. We can make good use of an authoritative source, the U.S. Department of Energy’s Steam Tip #8 by quoting from it in this Mechanical Seal Energy Audit:

Using separator pumps as a case in point, these pumps are taking condensate off the condensate receiver tank after the paper machine rolls. It is not customary for the receiver level controls to be manually overridden. Overrides can occur when the machine is brought on-line and steam must be kept in the rolls to prevent these from flooding. As steam enters the separator pump, the mechanical seal face set cannot seal steam. The lapped faces will become distorted and severe leakage will result.

Condensate pumps traditionally use API Plan 02, API Plan 11, API Plan 21, or API Plan 23. These plans use a single mechanical seal with one of these plan options.

The graphic on the next page shows hypothetically where each plan operates on a vapor-temperature curve for condensate. In order to understand how the traditional plans have been used, assume the condensate pump has a suction pressure of about 30 psig and the condensate is 200 degrees Fahrenheit (93 degrees Celsius). The discharge is 80 psig and there is naturally no change to the discharge temperature. For discussion purposes, the seal generates heat; assume the resulting temperature increase is 25 degrees Fahrenheit (-4 degrees Celsius). What is the pressure in the seal chamber? The seal chamber pressure depends on the pump design. Vanes on the back of the impeller or balancing holes near the eye of the impeller are used in design to control the axial thrust on the pump shaft. These pressure balancing techniques mean the pressure in the seal chamber will be closer to suction pressure. Again, it depends on the pump and seal manufacturers usually recommend consultation with the pump manufacturer to verify this pressure.

Seal chamber pressure and temperature: Pressure is just above the vapor point and the pump is pumping a liquid (water/condensate). The temperature and pressure in the seal chamber are such that the seal chamber contents are still in the liquid state.

API Plan 02. Depending on the actual pressure in the seal chamber, the seal faces generate heat and a pressure drop occurs across the seal face from 40 psig to 0 psig. Therefore, the fluid film between the seal faces could be vaporizing (“flashing”) as temperature increases and pressure drops.

API Plan 11 has been selected for this service. This plan increases the seal chamber pressure to 80 psig, assumes no cooling for seal face generated heat. The safety margin comes from higher pressure.

API Plan 21. A heat exchanger has been added to the discharge bypass line and the pressure is raised while the product is cooled. The safety margin comes from higher pressure and cooling of the condensate.

API Plan 23. The seal chamber is isolated and product is circulated through a heat exchanger. The mechanical seal circulates the liquid with a pumping ring (a “flow inducer”). This plan is more energy efficient than Plan 21 because the cooler only removes the heat generated primarily by the seal. There is also a small amount of heat soak from the process that passes an internal isolation restriction bushing in the seal chamber.

Failure: At any point during the life of the rotating equipment, if the pump sees steam because of operational upsets or the condensate receiver level causes the pump to run dry, the mechanical seal fails and the condensate pump leaks. This is the core issue to address.

The solution recommended is to use a dual seal with a secondary fluid consisting of treated clean condensate. The purpose of the secondary fluid is to cool the seal faces during normal operation and to serve as a lubricating fluid when the pump runs dry or steam is forced through the pump. This deals with the core failure issue of dry running or steam being forced through the pump.

By using a dual seal arrangement to mitigate the dry-running conditions caused by operational upsets affecting the condensate receiver, the user should expect years of leak-free service and energy efficiency benefits outlined in the Department of Energy Steam Tip #8.

Tom Grove is an executive vice president at AESSEAL Inc., one of the world’s leading specialists in the design and manufacture of mechanical seals and support systems. He can be reached at tom.grove@aesseal.com. Heinz P. Bloch, P.E., is one of the world’s most recognized experts in machine reliability and is a Life Fellow of the ASME, in addition to having maintained his registration as a Professional Engineer in both New Jersey and Texas for several straight decades. As a consultant, Mr. Bloch is world-renowned and value-adding. He can be contacted at heinzpbloch@gmail.com.

API 682 has created definitions for many of the common features and attributes of mechanical seals and systems. When new concepts are introduced or options are added to the standard, they must be captured in the definitions.

Type A is a balanced, cartridge mounted seal which utilized elastomeric secondary seals. Type B is a cartridge mounted seal which utilizes the flexible metal bellows and elastomeric secondary seals. The Type C Seal is a cartridge mounted high temperature bellows seals which utilizes flexible graphite secondary seals. Other requirements such as face materials and elastomers are tied to these definitions.

This article contains excerpts from the paper, "Advancements in mechanical sealing -- API 682 Fourth Edition" at the 2013 International Pump Users Symposium held at Houston, Texas.

The Fourth Edition of API 682 expands on these definitions slightly. Type A and B seals have historically been defined as having flexible rotating elements. This means that the springs or bellows assembly will rotate with the shaft. This was selected as the default design in the First Edition due to the high population of these designs in the refinery industry. Type C seals have historically defaulted to stationary flexible elements.

The A.R. Thomson API seal lineup represents the next generation in mechanical sealing technology for the oil and gas sector. We utilized state-of-the-art technology in materials, manufacturing, design, and inspection to deliver the best Mean Time Between Failure (MTBF).

One of the often-overlooked advantages of our mechanical seal line is the flexible stationary element, where we place the seal springs on the stationary seal face. This design choice provides advantages over legacy flexible rotating elements—offering the best MTBF.

When the seal springs are located on the stationary face, they adjust to any angular misalignment automatically and, once adjusted, stay there. This prevents fatigue on the seal springs and stabilizes the fluid film.

Flexible rotor seals are limited to a maximum surface speed of 20 m/s, meaning larger diameter high energy equipment will start to see dynamics issues with the springs at speeds above 3000 rpm and balance diameters over 4.5.” Our stationary design is rated to at least 25 m/s, making this seal the prime choice for larger, high-energy equipment seen in today’s oil and gas market.

Improved environmental awareness shows that legacy single seal designs do not provide the necessary containment for fugitive emissions. They also provide no containment in the event of primary seal failure. Unfortunately, older API610 pumps often don’t have the space necessary to fit a readily available dual API seal.

The design of the Thomson API seal allows for a completely new approach to fitting dual seals into a small envelope. Removing the need for expensive replacement of rotating equipment and costly plant redesign.

With over 100 years of combined mechanical seal experience within our engineering group, we can reverse engineer any seal and determine and supply the correct face materials.

Mechanical seals are intricate engineered products that may require service work—typically after a machine outage or failure. Simply repairing a seal is not always enough.

At A.R. Thomson, we believe the level of detail we can provide is unmatched. Our reports can tell you if the seal was installed correctly and confirm the concentricity of an install to within 0.025mm—well inside any OEM install requirements.

Face blisters can be challenging to diagnose in a seal failure. Often, they are too small to see with the naked eye. A.R. Thomson has the equipment necessary to show face topology in minute detail. This enables us to deliver the full story of the seal faces to the customer, face blisters, heat checking, and eccentric installation. We can show it all!

For more information on A.R. Thomson Group’s Mechanical seal service, to see an example of our failure reports, or more information on our line of API & TAC Mechanical Seals, please call 780.450.8080 or learn more about our API seals here.