Analytical Model and Numerical Analysis of Composite Wrap System Applied to Steel Pipeline

Composite overwraps are a cost-effective repair technology, appropriate for corrosion defects, dents, and gouges for both onshore and offshore steel pipelines. The main benefit of polymer-based sleeves is safe installation without taking the pipeline out of service. This paper presents a new calculation procedure proposed in the form of an algorithm for the sizing of composite repairs of corroded pipelines when the sleeve is applied at zero internal pressure. The main objective of the presented methodology is determination of the effective thickness of the composite repair without its overestimation or underestimation. The authors used a non-linear finite element method with constitutive models allowing analysis of the steel, putty, and composite structures. The validation of the results of numerical computations compared to the experimental ones showed an appropriate agreement. The numerical calculations were applied to compare the analytical results in relation to those obtained by the standards ASME PCC-2 or ISO/TS 24817. The comparison showed that the proposed solution confirmed its effectiveness in reducing the thickness of the sleeve significantly, thus, showing that the current industrial standards provide a considerably excessive composite wrap around the steel pipe corroded area, which leads to an unnecessary increase in the repair costs.

Reparo em resina composta usando adesivo universal melhora a estabilidade da união

Repair in resin-based composite is a procedure that has shown good results, when properly indicated. In cases of fracture or stainning, the total removal of the restoration can cause unnecessary wear on the dental element. This study evaluated the aging effect on the bond strength of a universal adhesive containing silane, and/or application of silane separately for composite repairs. Resin composite blocks were thermocycled and divided according to adhesion protocol (n=10): silane(Sil), conventional adhesive(CA), universal adhesive(UA), Sil+CA(SilCA), and Sil+UA(SilUA). Layers of resin composite were added and blocks were sectioned and divided into 2 subgroups: 24h and 4 months of water storage. Microtensile bond strength test was performed and data were statistically analyzed (a = 0.05). After 4months of aging SilCA and SilUA showed a significant bond strength reduction, while for UA the bonding remained stable.

Repair and Reinforcement of Blunt Defects on Pipeline Bends Using Composite Materials

Previous research on the use of composite repair systems has focused on the repair of damage to straight sections. This paper reports verification testing completed on composite repairs for pipeline bends to support development of a safe and consistent approach that ensures an equal level of performance is maintained over the entire system. A series of finite element analyses were completed that considered the effects of bend size (diameter and wall thickness), material grade, bend radius and angle. From this work 90° , 1.5D, 12” NB, X52 bends were selected for test. The objective was to demonstrate restoration of the fatigue life of the pipe to acceptable levels rather than just considering burst pressure. Defects equal to 0.5 times the diameter axially and 0.25 times the diameter radially were machined into the intrados of the bend (the location of highest hoop stress). Wall losses of 20% and 80% were replicated. Bounding repair thicknesses were tested to confirm performance was predictable. Aggressive cyclic pressure ranges of 125Nmm−2 and 90mm−2 were applied to the repaired defects, with the lower stress range loaded for a larger number of cycles. A successful test was defined as one which exceeded the target number of cycles by a factor of 10 AND for which there was no visual sign of repair degradation. The number of load cycles was selected to ensure the repaired lines satisfied the slope of the S-N curve for pristine pipe, confirming the approach maintained the required margin of safety applicable to the rest of the system. A design method is proposed that addresses weaknesses in the methods given in ISO 24817 and ASME PCC-2 Article 401. It is proposed that this be adopted by the standards for repairs to high pressure gas transmission pipelines to ensure equality of performance with undamaged sections.