Fatigue: Every Run Costs a Little Life
Coiled tubing is a continuous string of flexible steel pipe spooled on a reel. Every trip bends the pipe twice, off the reel and over the gooseneck, then back again. The bending is plastic. Each cycle does permanent damage to the steel. That damage is fatigue, and the string has a finite fatigue life. Every run consumes part of it, so operators track each job against the string's running history. Push a string past its fatigue life and it can part downhole. A parted string is a fishing job and a well control risk. That is why fatigue tracking is a core safety task, not paperwork.
The Injector Head: How the String Gets In and Out
The injector head is the drive of the unit. Hydraulically driven chains grip the tubing and push it into the well or pull it out. The head also straightens the string just before it enters the borehole. From the control cabin the operator runs the head to control depth and speed. Pre-job checks cover chain condition, gripper blocks, and hydraulic pressure. A worn gripper or a slipping chain means loss of control at the surface. Check the head before rig-up, not after a problem.
The Well Control Stack: Stripper and BOP
Below the injector head sits the well control stack. The stripper provides a dynamic seal around the moving tubing. That seal is what allows work on live, pressurized wells. The blowout preventer below the stripper is the secondary barrier and the contingency plan. API RP 16ST covers the assembly and operation of this equipment for coiled tubing work. The stack is pressure tested before the job, and the test is recorded. A stack without a current test record is a stack that cannot be trusted. The RP does not cover hydrostatic balance with fluids; that belongs to the well plan.
Coiled tubing safety comes down to records and checks: fatigue life used, equipment inspected, pressure tests current. Pair them with BOP testing and well control drills, watch H2S monitoring at the wellsite, and run a job safety analysis before every shift. Then close the loop with an operations audit so the paperwork is as tight as the equipment.