Efeito do golpe de aríete em sistemas de reparo com patches metálicos colados

Abstract

This study experimentally investigates the structural behavior of bonded metallic patch repair systems applied to pipelines with simulated through-wall defects, when subjected to different pressure loading rates. The tests were performed on API 5L Grade B steel pipes repaired with ASTM A36 steel patches bonded using a structural epoxy adhesive, and subjected to monotonic hydrostatic loading and high-rate pressure loading representative of transient conditions associated with water hammer. Hydrostatic tests were carried out in accordance with ASTM D1599, with continuous monitoring of the failure pressure and the time to failure of the repair system. The experimental results showed a significant variation in failure pressure as a function of the pressure loading rate, indicating a rate-dependent behavior associated with the viscoelastic response of the adhesive layer. While slow loading tests resulted in failure at considerably lower pressures, tests with rapid pressure increase led to failure pressures up to five times higher. Based on the experimental findings, an analytical approach is proposed to estimate a conservative lower bound for the failure pressure of the repaired pipe, grounded on concepts of Linear Elastic Fracture Mechanics and the critical energy release rate. In addition, the need for corrections to traditional bonded repair design criteria is discussed in order to account for pressure peaks induced by pressure transients and for the loading-rate dependency of the adhesive layer. The results indicate that the explicit consideration of transient effects is essential for a more realistic assessment of the integrity and reliability of bonded repair systems applied to pipelines operating under dynamic pressure conditions.