API Standard 682, titled "Pumps - Shaft Sealing Systems for Centrifugal and Rotary Pumps," is the American Petroleum Institute (API) standard for end-face mechanical seals. The purpose of API 682 is to assist in the selection and operation of end face mechanical seals in centrifugal pumps. It is based on the combined knowledge and experience of seal manufacturers, engineering companies, and end users. API 682 is primarily intended for use in the petroleum, natural gas and chemical industries, but is often referenced for other types of equipment and industries.
The API has approximately 500 technical standards for processes and components.
Background and development
By the late 1980s, mechanical seals had been accepted as the preferred method for sealing rotating pumps for many years. However, mechanical seal standards were generally buried in other standards such as DIN 24960, ANSI B73, and API 610. All of these standards were primarily pump standards and any references to seals were directed at how mechanical seals would interact with pumps.
API 610 is the API standard about centrifugal pumps and is primarily intended for use in the petroleum, natural gas and chemical industries. Although the 1st through 7th Editions of API 610 included specifications for mechanical seals, beginning with the 8th Edition, API 610 defers to API 682 for seal specifications.
In the late 1980s a group of refinery equipment engineers and managers began to compare sealing solutions in refinery applications. This group, led by V. R. Dodd of Chevron, came up with a general plan and the American Petroleum Institute (API) agreed to establish a standard for mechanical seals: API 682. A Task Force was formed in 1990 and the first meeting was held in January 1991. This Task Force was composed of fourteen members from various refineries, seal and pump manufacturers. API 682, First Edition, was published in October 1994.
One interesting aspect of API 682 is that it includes a strong set of defaults. That is, unless the user indicates otherwise, API 682 makes default choices for specifics such as: Seal type Rotating or stationary Seal arrangement Seal configuration/orientation Materials Piping plan … many others.
Some statements within API 682 are normative, that is, required, whereas others are informative, that is, descriptive but not required. In particular, many of the illustrations are informative. This distinction has not always been apparent to the reader.
Subsequent editions of API 682 have been published. The current edition is 4th Edition.
API 682 1st edition
The first edition of API 682 was entirely new although parts of it were extracted from the pump standard API 610 and existing API standard paragraphs.
The mission statement for the 1st Edition was:
"This standard is designed to default to the equipment types most commonly supplied that have a high probability of meeting the objective of at least three years of uninterrupted service while complying with emissions regulations."
Although this mission statement no longer appears in the standard, it remains the basic principle driving the work of the API 682 Task Force and its relevance remains the same for the 4th Edition as it did for the 1st.
In addition to providing requirements for mechanical seals, the 1st Edition of API 682 also provided a guide on how to select the correct seal for a number of common refinery applications. In order to provide this seal selection guide, it was necessary to categorize applications into a number of services: Non-hydrocarbon water sour water caustics/amines acids Non-flashing hydrocarbon Flashing hydrocarbon.
It was also necessary to categorize the many different type seals that were used in these services. Three seal types were designated: Type A – O-ring pusher Type B – O-ring metal bellows Type C – flexible gasket (high temperature) metal bellows.
Prior to API 682, 1st Edition, multiple seals were designated as being either “tandem” or “double” seals; however, advances in seal design had rendered these classic terms obsolete. As a result, there was some confusion on how multiple seals were designated. The task force decided to use a more descriptive designation and chose to define dual seal arrangements. A dual seal would be two sets of sealing faces used in the same seal chamber. The fluid between these two sets of sealing faces could be either pressurized or unpressurized. Three standard arrangements were defined: Arrangement 1 is a single seal Arrangement 2 is a dual unpressurized seal Arrangement 3 is a dual pressurized seal.
API 682 1st Edition did not include containment seals or dry gas barrier seals.