Analysis of burst tests and long-term hydrostatic tests in produced water pipelines

The present work is concerned with the analysis of special hydrostatic tests performed in metallic pipelines used to convey produced water in offshore oil and gas platforms. The goal is to evaluate the strength of a pipeline with through-thickness corrosion damage when repaired with special epoxy systems. Burst tests and long-term hydrostatic tests at constant pressure levels performed at the operation temperature (between 353 K and 363 K) are generally recommended for assessing the structural integrity of these repaired pipelines. Elastoplasticity theory and thermodynamics are used in the modelling of these tests. The goal is to propose phenomenological models, as simple as possible, able to perform a physically realistic description of the non-linear phenomena. In the case of hydrostatic tests, it is shown that that both yield and burst pressure can be related with the yield stress and ultimate stress obtained in a tensile test. In the case of long-time tests, special attention is given to the explanation of why huge pressure peaks may be induced by a very small temperature variation if an inadequate pressure control system is adopted. Model predictions are compared with experimental results showing a good agreement.