Most drilling rigs have catheads on each side of the drawworks which are used to apply line pull to the tongs. The catheads do not have built in devices to measure the amount of line pull. Line pull measuring devices must be added to the lines between the tongs and the catheads to accomplish this task. The driller is required to release the cathead clutch at the appropriate time in order to ensure the desired pull is not exceeded. This often causes errors in application of the torque.
Hydraulic Load Cells
For measuring the amount of applied line pull, many rigs use hydraulic load cells. Load cells are simple devices that are generally very reliable. A load cell device usually consists of three parts: (1) a small hydraulic cylinder, (2) a pressure gage that reads pounds of pull, and (3) a rubber hose to connect the cylinder and the gage. One must remember that the gage reads in pounds of force and not in foot-pounds of torque. You must measure the length of the tongs in feet. And then you multiply the gage reading (pounds) by the tong length (feet) to get foot-pounds of torque.
Automatic Torque Control System
Service Companies provides a system that eliminates the problems associated with using the rig catheads. This product is called the Automatic Torque Control System (ATCS). The ATCS is a highly accurate solidstate electronic control that automatically terminates makeup of the drill stem connections when the prespecified torque is reached. It can be used on any rig that has manual tongs and air-activated cathead clutches. With a few modifications it can be adapted to hydraulic makeup systems. The ATCS includes an intrinsically safe load cell, explosion-proof air controllers and an airpurged control panel for operation in Class 1, Group D, Divisions 1 and 2 hazardous environments. For operation in all Division 1 situations, a power time delay unit is required.
How Does the ATCS Help?
· Safer - The driller is freed from watching hydraulic torque gages for the make up of each connection, thus letting him focus his attention on the rig floor activities.
· Reduces trip time - Automatic application of makeup torque results in faster and optimum rig floor rhythm of movement.
·Reduces pin and box damage - Improper torque is the primary cause of swelled boxes, stretched pins, and galled threads and shoulders.
· Minimizes risk of fishing jobs - Improper makeup torque causes washouts and twistoffs.
·Reduces rig downtime - By eliminating torquerelated failures, you can avoid the expense of laying down damaged pipe and tools, repair or replacement, and loss of costly rig time.
Hydraulic Line Pull Devices
Sometimes drilling rigs do not have catheads or have catheads with insufficient capacity or simply do not want to use them for the makeup of large rotary shouldered connections. In these cases, the rig must rely on external devices to supply the line pull to the tongs. These devices take the form of hydraulic cylinders and power sources.