Disc Couplings in Oil & Gas Applications


Written by:
Matt DeFord, Ameridrives -TB Wood’s Couplings

Make easier pump connections while meeting rigorous API 610 Standards

The oil and gas industry uses a wide range of pumps in typical power train configurations. Most oil and gas pump installations—including offshore platforms, oil and gas refineries and processing facilities—are required to meet American Petroleum Institute (API) 610 standards. API 610 outlines the minimum standards for pump safety, reliability and maintenance in these hazardous environments.

A new coupling technology, originally designed for the API 610 market in Europe, has entered the North American market. It can handle the harsh conditions of oil and gas applications.

The coupling and cold-install hubs

Flexible Disc Couplings

The new disc couplings are compliant with API 610, and the more demanding API 671 standard can be achieved. In addition, the couplings are certified to meet ATEX 94/9/EC ratings for Group 2/Category II standards. It employs anti-sparking overload washers, with operational characteristics that include no maintenance, zero backlash and easy interchangeability. They feature all-metal construction and require no lubrication. To allow for installation and removal without disturbing the pump alignment, they incorporate a plug-in spacer design. 

These API-compliant couplings also feature a robust disc pack design, which allows for a greater torque load in a smaller coupling, reducing the coupling weight. Max bores matched to NEMA motor shafts provide up to a 60 percent weight savings. Combined with longer bearing life, this provides a lower cost per application. 

The coupling’s large bolts provide a high clamp load, enabling an increased frictional torque load and reduced bolt-bending stress. A smaller diameter and lower weight per horsepower provide better inherent balance. Hub attachment screws come in both English and metric sizes. Torsionally stiff and backlash free, the coupling also incorporates an anti-flail feature. Spark-free overload protection is standard on all units, making them ideal for use in gas-zone environments. They are available with load ratings from 0.26 kNm to 85 kNm (2,300 pound inches to 1,062,000 pound inches.) and speeds from 3,600 to 8,000 rpm.

 In most applications, the couplings are fit-and-forget units. They have no moving parts, so they require no maintenance. They need no lubrication. However, the presence of oil in the environment will not affect the operation of the coupling. This is achieved by using large aircraft-quality disc pack bolts that are larger than those used by other couplings. As a result of this design, the disc packs in the coupling can be clamped harder together to prevent fretting. Reduced fretting reduces the possibility of premature coupling failure.

Cold-Install Hubs Meet Industry Demand

Also available are cold-install hubs that provide the secure torque transmission and balance repeatability of an interference fit. Incorporating these cold-install hubs with the new coupling addresses heat and flame concerns by eliminating Hot Work Permits associated with shrink fitting typical coupling hubs. 

Shaft locking devices on the disc couplings provide a pre-engineered solution that meets the balance requirements of API 610. The cold-install hubs offer the ease of a slip fit with the power of a shrink fit. They
provide easy, repeatable removal and installation and eliminate hub to shaft fretting. The hubs can also compensate for variances in shaft spacing. Units can be slipped on and fixed in place at the needed location. The hub and locking device are balanced and match-marked to assure optimum balance performance. 

The hubs can be specified for one or both coupling hubs and sized to accommodate a variety of shaft diameters. The hub and new coupling combination may be used with keyed or keyless shafts, but a half-key is recommended with keyed shafts to reduce unbalance. 

The cold-install hubs provide the ease of slip fit with the power of a shrink fit.

Construction Materials

By carefully selecting the proper materials, permanent shrinkage of the hub to the shaft was prevented. The hubs, spacers and adapters are made of carbon steel. The disc couplings are made of stainless steel (301), while alloy steel is used for bolts and nuts. The overload collars are made of a proprietary high-strength non-sparking material.

End users may specify alternative materials for specific applications. Special coupling versions are available for torque overload protection, limited end float, applications requiring electrical insulation and long spacer designs. Bolted adapters suitable for high cyclic torques are available. 

Oil & Gas Applications

The couplings mated with the cold-install hubs can be used to connect pumps to motors in many petrochemical industry applications—such as offshore oil platforms, oil processing facilities and gas processing plants, including liquefied natural gas (LNG) plants. They also can be used in oil refineries, chemical processing plants, power stations (boiler feed water pumps) and cogeneration power plants.

During the initial introduction of the couplings to the refinery market, the customer reaction to the design features that this coupling brought to equipment reliability was positive. The lighter weight, balance characteristics and interference fit hubs without heat use were positive characteristics for end users. 

One major refinery on the Gulf Coast looked for an alternative to using heat for mounting hubs for several years. The new disc couplings and cold-install hubs were the answer.

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See also:

Upstream Pumping Solutions

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