A kelly hose is a piece of mining equipment. Specifically, it refers to a piece of equipment used in the mining of fluid or semi-fluid resources, such as oil and natural gas. The main purpose of a kelly hose is to allow the drill string to be raised and lowered at the same time that drill fluid is being pumped through it. This is important, as drill fluid is critical to the mining process.
In most cases, a kelly hose is classified as a large-diameter hose. This means that the inside diameter is usually between 3 and 5 inches (about 7.6 cm and 12.7 cm). This wide diameter allows for a significant rate of flow and reduces the likelihood of a blockage occurring in the hose.
The kelly hose must also be able to withstand large amounts of pressure. This applies primarily to the pressure of the fluid flowing through the hose. For this reason, it is often made of highly durable material and is generally reinforced with steel.
In a derrick or drilling rig, the kelly hose connects the standpipe, which is the rigid metal shaft that delivers the mining fluid, to the swivel, which is the piece that supports the weight of and controls the rotation of the drill string. Its purpose is to provide a flexible drilling fluid conduit, as a rigid conduit would be unable to move with the swivel and would therefore disallow movement of the drill string and, subsequently, the bit.
The drilling fluid, sometimes called drilling mud, carried by a kelly hose is critical to operations in several ways. It keeps the bit cool, which helps reduce friction and failure. It also cleans the bit and carries away drill cuttings so they cannot damage the drill assembly. Some varieties are used for additional purposes, such as preventing corrosion and providing hydrostatic pressure. Drilling fluid is not necessarily fluid, but may, in fact, be a solid, liquid, gas or other combined form.
The kelly hose is so named because of its connection with the kelly, the actual mechanical piece that ejects the drilling fluid over the drill string. It may alternatively be called a mud hose or a rotary hose. Failure can occur, despite the rugged construction of the hose. Such failure can lead to damage to the rig or a failure to operate. Failed kelly hoses must be repaired or replaced before mining operations can safely and effectively resume.
