Paper: Using The API Specification 11C And The Stress Range Diagram

The fatigue life of a reinforced plastic sucker rod is controlled by minimum stress, the stress range, and the operating temperature. The diagram, Figure 1, is part of API Specification 11C. For any minimum stress found on line 0-1, a peak allowable stress is found directly above on line A-P. If a well is operating at 100 percent of this allowable range with an operating temperature of 160F, it should cycle 7,500,000 times before expected first failure. Column B and Column D allow the stress range to be modified for different life expectancies and different operating temperatures. Figure 2 is the stress range diagram for Fiberflex fiberglass sucker rods. Two different parts of the rod must be considered when estimating fatigue life: the rod body and the end connector system.