PR-201-154500-R01 Composite Repair Load Transfer Study
Authors: Sheets Colton 
Published: August 2023

The objective of the PRCI MATR-3-11 Composite Repair Load Transfer Study was to evaluate the effect of internal pipe pressure during installation of composite reinforcement systems. Historically, there has been little work evaluating the effect of internal pressure during installation, even though almost all composite installations on transmission pipelines are performed with internal pressure present in the pipe. The focus of this work was specifically limited to reinforcement of pipelines containing simulated corrosion anomalies. Five composite repair technologies from four composite manufacturers were evaluated in this study including:

� Western Specialties Ultra-Wrap (E-glass/epoxy)

� Western Specialties Composi-Sleeve (steel sleeve with E-glass overwrap)

� Citadel (carbon fiber/epoxy)

� Furmanite (carbon fiber/epoxy)

� NRI Steel Wrap (high-modulus carbon fiber/epoxy)

This study used full-scale testing to analyze the load transfer between the composite repair and pipe with internal pressure present during installation and whether this condition impacts the reinforcement provided by the composite repair system. The anomaly configuration evaluated in this study was a machined corrosion defect simulating 50% wall loss in 12.75-inch x 0.375-inch, Grade X42 pipe material. For safety, internal pressure during installation was limited to 50% SMYS (1,236 psig) for the corrosion samples. The composite repairs for the corrosion defects were installed at internal pressure levels of 0 psig, 25% SMYS (618 psig), and 50% SMYS (1,236 psig). Following repair installation, the reinforced full-scale samples were burst tested or pressure cycled to failure to evaluate the repair's performance.

Results indicated that, in general, internal pressure during installation did not significantly impact the ability of the composite systems to reinforce the corrosion anomalies evaluated in this study when installed at or below 50% SMYS. Installation pressures up to 50% SMYS had no noticeable effect on the burst pressure of the corroded sample composite repairs, and the burst pressure of all repairs were equivalent to pressure levels for an unreinforced, undamaged pipe. Also, all repairs failed at approximately the same average burst pressure, regardless of installation pressure. Furthermore, installation pressures up to 50% SMYS had little or no noticeable effect on the fatigue life of reinforced corrosion samples; all sample repairs reached the target runout of 250,000 cycles.

Observations from the burst testing suggested that loads from the corroded region were not transferred to the composite repair until the corroded region began to yield, regardless of the pressure at which the composite was installed (applicable for installation pressures at or below 50% SMYS and a corrosion depth of 50%).

The results and findings of this study provide valuable information to the pipeline industry for addressing an issue of significant interest for many years, and one not previously addressed in a comprehensive manner via full-scale testing. An important observation from this study is that the performance of composite repairs made on corrosion defects does not appear to be appreciably reduced when internal pressures up to 50% SMYS are present during installation.