This is the brief explanation of a Kelly rotating system on the rig. Kelly rig is on an old style rigs and nowadays it is mostly used on land operations. For offshore operation, a top drive system is used instead.
First of all, it is important for new people to look at these images before reading the information below because they show the equipment’s name and where they are on the rig.
Mast and derrick are used to support load from hoisting system and drilling load. However, they are different.
Referring to the API definition, a mast is a structural tower comprised of one or more sections assembled in a horizontal position near the ground and then raised to the operating position. If the unit contains two or more sections, it may be telescoped or unfolded during the erection procedure. Generally, masts are assembled on the ground in a horizontal position and then are raised using the draw works. Some masts use telescopic sections and are assembled in a vertical (boot strap) fashion. Masts are normally used on land rigs; they are rarely used on offshore rigs.
