A testing program was conducted to evaluate the effects of internal pressure during the installation of composite and steel sleeves repair systems on pipelines with plain dents. The testing program included cyclic pressure testing a group of 12.75-inch OD x 0.188-inch WT, Grade X42 pipe samples with plain dents having residual dent depths on the order of 3% to 4% of the pipe’s outside diameter. The dent samples were repaired using four (4) different composite repair systems, type-A steel sleeves, and steel thermal compression sleeves. The composite repair systems included a carbon fiber ...
A testing program was conducted to evaluate the effects of internal pressure during the installation of composite and steel sleeves repair systems on pipelines with plain dents. The testing program included cyclic pressure testing a group of 12.75-inch OD x 0.188-inch WT, Grade X42 pipe samples with plain dents having residual dent depths on the order of 3% to 4% of the pipe’s outside diameter. The dent samples were repaired using four (4) different composite repair systems, type-A steel sleeves, and steel thermal compression sleeves. The composite repair systems included a carbon fiber wet-layup, an E-glass wet-layup, a system with precured plies, and a hybrid composite-steel repair system. To determine the effect internal pressure has on repair installation for dents, all repairs were installed with an internal pressure of 64% SMYS (793 psig) in the pipe sample. The dent samples were then pressure cycled between 8 – 80% SMSY (ΔP = 900 psig) until failure or reaching the runout condition of 250,000 cycles. Only three (3) out of the fourteen (14) repaired dents reached the 250,000 pressure cycle runout condition and these samples were all repaired using steel sleeves. The maximum number of cycles reached by any composite repair was approximately 200,000 cycles while the least number of cycles reached was approximately 24,000 cycles.
In addition to the dent repairs, two (2) 12.75-inch OD x 0.375-inch WT, Grade X42 pipe samples with a 6-inch x 8-inch corrosion defect were repaired with an E-glass wet-layup. These two (2) samples were a continuation of a previous study that investigated the effects of a 50% SMYS (1,235 psig) installation pressure on the fatigue performance of corrosion repairs. Both samples reached the runout condition of 250,000 cycles.
The body of work is seminal in that it is the first time that industry was evaluated a wide range of repair technologies to determine the effects of pressure during installation in reinforcing plain dents. It has been speculated for some time that internal pressure present during installation of composite repair technologies has an impact on fatigue performance. Although corrosion features do not appear to be a concern, the reinforcement of dents with internal pressure requires careful consideration. Because gas transmission pipelines do not experience aggressive pressure cycling, the effects of pressure present during installation are not a major concern. However, liquid transmission pipeline operators should be cognizant of the pressure effects and respond accordingly. Namely, pressure should be reduced during installation as much as possible.