January 16, 2020 | 3 minute read
Major industry companies, such as big oil and gas suppliers and petrochemical refiners, have very detailed specifications for equipment like pumps, turbines and mechanical seals, and already know what their seal preferences. This may not so much be the case with smaller industrial producers and manufacturers. But regardless of company size, plant engineers and facility managers universally accept American Petroleum Institute (API) Standard 682 as the industry benchmark for specifying shaft sealing systems for centrifugal and rotary pumps.
The idea is that the person requiring a seal can go through API 682 and arrive at a selection that will be a reliable option. The following are factors to keep in mind when referencing the Standard for seal selection and operation.
Knowledge and Experience Based
The purpose of API 682 is to assist in the selection and operation of end-face mechanical seals. It is based on the combined knowledge and experience of seal manufacturers, engineering companies and end users.
Scope of the Standard
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. Those who use the Standard should understand its scope, and know that the standard does not include specifications for equipment outside of that scope, such as engineered seals or mixers.
Figures Are Illustrative
An important, but often misunderstood point is that API 682’s figures are illustrative and not normative in their entirety. The standard provides normative details in clauses and tables to help purchasers distinguish between requirements and suggestions.
Mechanical Seal Designs
The latest 4th edition of the API 682 Standard continues to divide seals into three categories, three types and three arrangements. For all practical purposes, seal manufacturers can combine a seal’s component parts into nearly any orientation or configuration. Each orientation and configuration has advantages and disadvantages with respect to certain applications, performance and system disturbances.
Defaults
The Standard includes a strong set of defaults. Unless the user indicates otherwise, the Standard makes default choices for specifics such as:
a) Seal type
b) Rotating or stationary
c) Seal arrangement
d) Seal configuration/orientation
e) Bushings
f) Materials
Technical Tutorials and Illustrative Calculations
And importantly, the 4th edition of API 682 expands the tutorial section, Annex F, including illustrative calculations that are meant to supplement the design requirement suggestions in the body of the Standard. There are sections around leakage, vapor pressure margins, containment strategy and devices, and temperature rise and flush rates. However, in all of these various sections in Annex F, there is a large volume of information that can be useful to better understand many of the requirements or suggestions called out in the body of the Standard.