الملخص الإنجليزي
Corrosion is one of the most common and serious threats to oil and gas pipelines.
Corrosion defects of random shapes can be found either as a single pit at one location
or multiple pits in near vicinity. Assessment of pipe integrity is very important to
maintain continuity of production, and to plan for repair and maintenance.
Experimental testing to predict behavior of corroded pipes is both time consuming
and costly. Numerical simulation can give reasonably accurate predictions without the
need for elaborate testing. In computational modeling or empirical testing, defect
shapes can be approximated by various polygonal or conic-section shapes, together
with their orientation and separation from each other. If corrosion defects are close to
each other, their interaction increases, resulting in lower failure pressure compared to
single defect. Finite element analysis (FEA) is used in this work to determine the
failure pressure, considering different parameters such as defect shape and geometry,
distance between defects, and defect orientation (longitudinal, circumferential, and
diagonal). Initially, results are compared with published findings from experimental
and numerical studies. After validation, simulated values of failure pressure are used
to determine burst and collapse strengths of corroded pipes. Parametric studies are
then conducted, including the effects of pipe diameter, defect depth, pipe wall
thickness, etc. Results show that existing codes are highly conservative which may
result in unnecessary shutdowns, repairs, or operation below design conditions. Some
notable conclusions are that the defect shape has small effect on pipeline failure
pressure, while the defect depth to pipe thickness ratio has a significant influence.
Defect location either internal or external and defects orientation have also a big
influence in pipe burst and collapse strengths as well as defects interaction. A new
correlation equation is proposed as a correction to standard equations to determine the
collapse failure pressure of a pipeline with two corrosion defects.
