API 682 (3rd edition) and ISO 21149 Standard (18-8)
The API 682 standard was originally published in 1994 as a guide to selecting seals in the petroleum industry.
- In 1998 the API developed a 2nd Edition, along with a joint program to convert the document into an ISO standard to be designated ISO 21049.
- The third edition of the standard was finally published in February 2004.
- All dimensions are in SI units with the US customary units given in parentheses.
- Please note that this new standard does not cover the design of the seal components. That decision is left to the individual seal manufacturers.
Here are some of the highlights of this standard:
There are three recommended seal categories:
- Category #1 intended for chemical duty pumps.
- Category #2 intended for API, requiring fewer features than a 682 first edition seal.
- Category #3 intended for API 610 pumps.
Each has a temperature range:
- Category #1 -40 C. to 260 C. (-40 F. to 500F.)
- Category #2 -40 C. to 400C. (-40 F. to 750F.)
- Category #3 -40 C. to 400 C. (-40F to 750F.)
Each has a pressure limit:
- Category #1 22 bar (315 psia.)
- Category #2 42 bar (615 psia.)
- Category #3 42 bar (615 psia)
There are some differences in the face materials*:
- Category #1 Anti-blister carbon vs. self sintered silicon carbide
- Category #2 Anti-blister carbon vs. reaction bonded silicon carbide
- Category #3 Anti-blister carbon vs. reaction bonded silicon carbide
*For seals requiring two hard faces the default material for both faces is silicon carbide.
Here are the recommended metal components:
- Category #1 Hastelloy C276 springs, 316 stainless steel metal components.
- Category #2 Inconel 718 bellows, 316 metal components.
- Category #3 Inconel 718 bellows, 316 stainless steel components.
The recommended elastomers (Secondary seals):
- Category #1 Fluroelastomer (Viton) O-rings
- Category #2 Fluroelastomer (Viton) O-rings
- Category #3 Flexible graphite
The mechanical seal designs are divided into several types:
- Type A Describes a pusher seal with a rotating flexible element, silicon carbide versus carbon faces, alloy C-276 springs, fluoroelastomerO-rings, and 316 SS metal components.
- Type B Is a bellows seal with a rotating flexible element, silicon carbide versus carbon faces, alloy C-276 bellows plats, fluoroelastomer O-rings, and 316 SS metal components.
- Type C Is a bellows seal with a stationary flexible element, silicon carbide versus carbon faces, alloy 718 bellows plates, flexible graphite secondary seals, and 316 SS metal components.
- Type CS Describes a containment, or backup seal in a dual un-pressurized seal arrangement. Its designed to operate at less than 10-psi for the life of the inner seal. When the inner seal fails, the containment seal is designed to run under full seal chamber conditions for a minimum of eight hours and prevent or minimize process fluid leakage to atmosphere.
- Type NC Is a non-contacting seal that is designed to intentionally create a hydrodynamic lift and operate with a specific face separation. This design is used primarily on dual pressurized gas seals. It may also be used on liquid or mixed phase applications.
One seal per cartridge assembly
- Contacting single wet seal with a fixed throttle bushing. Configuration 1CW-FX
- Contacting single wet seal with a floating throttle bushing. Configuration 1CW-FL
Two seals per cartridge assembly with an externally supplied lower pressure buffer fluid between the seals.
- Liquid buffer fluid
- Dual contacting wet seals. Configuration 2CW-CW
- Gas buffer fluid, or no buffer fluid
- Contacting wet inner seal with a containment seal. Configuration 2CW-CS
- Non-contacting inner seal with a containment seal. Configuration 2NC-CS
Two seals per cartridge assembly with an externally supplied higher pressure barrier fluid between the seals
- Liquid barrier fluid
- Contacting wet seals, tandem configuration. Configuration 3CW-FB
- Contacting wet seals, back-to-back configuration. Configuration 3CW-BB
- Contacting wet seals, face-to-face configuration. Configuration 3CW-FF
- Gas barrier fluid
- Non-contacting seals, tandem configuration. Configuration 3NC-FB
- Non-contacting seals, back-to-back configuration. Configuration 3NC-BB
- Non-contacting seals, face-to-face configuration. Configuration 3NC-FF
The standard also covers:
- Accessories such as:
- Seal coolers, buffer/barrier fluid reservoirs, condensate collection reservoirs, and buffer/barrier gas supply panels,
- Seal qualification tests.
- During testing, the seals must maintain a leakage rate of less than 1000-ppm (as measured by EPA Method 21) or 5.6-gr/hr. This leakage criterion does not apply to testing of dual gas seals or containment seals under failure conditions. In addition, the measured wear on the seal faces must be less than 1 percent of the available wear.
- Seal hydrostatic testing
- Hydrostatic testing is required for the seal gland, all piping, reservoirs, and other auxiliary equipment exposed to process fluids.
- In the second and latter editions, there is an exemption for seal glands machined from a single piece of wrought material or bar stock.
- Cast seal glands still require testing.
- There are many annexes that include references, calculation techniques, and tutorial information. Here are two examples:
- Annex F – Mechanical seal data sheets
- One set of datasheets covers Category 1 and 2 seals. Another set covers Category 3 seals.
- These datasheets are provided in both SI and U.S. customary units.
- Annex J – Mechanical Seal Coding
- The first position of the code defines the category and is designated as C1, C2, or C3.
- The second position defines the arrangement and is designated as A1, A2, or A3.
- The third position defines the seal type and is designated as A, B, or C.
- The last position defines the piping plan(s) and is designated by the two-digit piping plan number. If more than one plan is required (such as on dual seals), the additional plans are added to the end of the code.
- Annex F – Mechanical seal data sheets
- Recommended seal selection procedures that are broken down into three process fluids:
- Non-flashing hydrocarbons
- Flashing hydrocarbons.
- Standard flush plans and auxiliary hardware. The following piping plans have been altered in this new edition
- 14, 53, 53A, 53B, 53C, 65, 71, 72, 74, 75, and 76
You should get a copy of these standards to learn how they all affect your plant.