A swivel is a piece of equipment that is placed in a pilot bore between the reamer and the pulling head during the back reaming operation. The swivel helps to keep the product pipe from rotating during the pullback process.
Trenchless drilling methods, such as horizontal directional drilling (HDD), involve the use of back reamers to expand the pilot bore to fit the product pipe inside the borehole.
Trenchlesspedia Explains Swivel
Swivels function on ball bearings and support axial loads by releasing the rotational torque on the drill string by providing a rotating link. The rotating link prevents the twisting of the string by keeping it in a neutral position. HDD projects make use of sealed greasable swivels because of the underground pulling operation that involves exposure to dirt, mud and lubricants such as bentonite.
The swivels are usually made from high grade pre-stressed steel to give better performance and long life. However; since it is exposed to a corrosive environment, their performance can be affected. For safety reasons swivels should always be inspected before and after use for damage or deformity.