Guarding requirements for API 671 couplings are similar to
all coupling guards as they must meet all applicable codes and regulations
(such as OSHA 1910.219). However, additional
requirements are included in the API 671 Standard. A few key features are:
- The ability to inspect the coupling without
requiring any additional work beyond removing the guarding.
- Capability to withstand a 200 pound static load.
- A minimum of 1 inch radial clearance between the
guard inner wall and coupling maximum outer diameter.
- Anti-swirl baffles installed as required to diminish
the effects of windage.
- Guards that are directly installed on the
machine base or bed plate should be removable as a single piece.
- No guarding should be constructed of woven wire,
only expanded metal, perforated plate or plate is permitted.
API 671 couplings are typically specified in critical
applications that operate for extended periods of time, are often non-spared,
have high torque and/or speed requirements.
Metallic flexible-element couplings are the primary type
permitted for API 671 (ISO 10441) applications.
Only disc couplings and diaphragm couplings can be used in API 671
applications. The application speed
& torque are the primary determining factors as to which type of metallic coupling
is best suited for the application. Gear
and quill shaft type couplings are permitted in the API 671 standard but are not
common.
While the coupling meets the API 610 requirements;
additional steps such as component serialization, precision balance, record
retention of 20+ years and an assembly print containing application information
are just some of the additional requirements needed to meet the API 671
specification. This is to ensure that a
high quality coupling was provided for a critical application and that spare
components can be produced decades into the future.
One feature of the API 671 specification are the various
methods allowed to achieve and measure the residual imbalance.
- Method 1 only requires the major components to
undergo balance verification but is limited to applications at or below 1,800
rpm.
- Method 2 is the standard for applications
operating above 1,800 rpm. While the
major components are balanced as with Method 1, the coupling is fully assembled
and the balance of the entire coupling is verified prior to shipment.
- Method 3 is similar to Method 1 where the major
components are individually balanced.
The coupling is then fully assembled and the coupling is balanced as a
single entity (where Method 2 only checked the balance of the coupling
assembly). One limiting item is that method 3 balancing removes the ability to
interchange coupling components (with the exception of disc pack units) as the
coupling assembly was balanced as a cohesive unit.
Recommended Follow-On Reading: To learn about API610 Couplings, we recommend: API 610 Standard - Coupling Highlights
