Heavy Weight Drill Pipe Specs is important to understand as it is the entrance of the heavy weight drill pipe design. In this article, we will discuss its specs and how to select in the drill string design. In addition to that, we will talk about its main functions. you can also download the specs sheets from any size of heavy weight drill pipes.
In the past, the two main components of the Drill String consisted of the Drill Pipe and the Drill Collars. The point where the relatively small OD and flexible Drill Pipe connects to the large stiff Drill Collars is called the Transition Zone. Oilfield studies have shown that almost all of the Drill Pipe fatigue failures are the result of an accumulation of fatigue damage occurring when the Drill Pipe joints were run in the Transition Zone or were stressed above the endurance limit in crooked holes. Downhole data has indicated that the large change in diameter at the transition zone caused accelerated fatigue damage as a result of the concentration of cyclic bending stress reversals in the bottom joints of the flexible Drill Pipe since the stiff Drill Collars bend very little from these stress reversals. So heavy weight drill pipe specs definition will be a drill pipes with higher thickness to withstand the stress in the transition zone.
Before starting ti talk about heavy weight drill pipe specs, let’s understand its function. Heavy weight drill pipe is used to absorb the stresses being transferred from the stiff Drill Collars to the relatively flexible Drill Pipe. The major HWDP benefits are:
Field tests indicated that fatigue build up in the Drill Pipe in the transition zone is related to the relative stiffness of the Drill Collars and the adjacent Drill Pipe. The stiffness ratio of two sections of pipe in the drill string is expressed by the equation,
The field tests showed that the higher the stiffness ratio at the transition zone the greater the fatigue build up. Criteria for permissible stiffness ratio varies between different operators and areas. The following maximums are typical:
In order to reduce the stiffness ratio and increase service life of the drill pipe, heavy weight drill pipe having the same OD as the drill pipe and a wall thickness of up to 1 in and weight up to 78 lb/ft is used between the drill pipe and the drill collars. The number of joints used varies between 15 to 21 joints.
Heavy weight drill pipe normally has the same external dimensions as the regular Drill Pipe. In some types of Heavy Weight Drill Pipes, the tool joints are longer and, in some types, an extra mock tool joint is located in the center of the joint as shown in the below drawing.
Heavy weight drill pipe specs vary for different manufacturers. Typical dimensions are shown in below table
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