When a leak happens on a pipeline, it is critical for pipeline operators to report an estimate of the volume of product released. This will be communicated to the required authorities under regulatory reporting requirements. An estimation of the total volume of released product in most incidents is challenging. This is attributable to factors that include: variation of the leak rate with respect to pipeline operating pressure; the hole/crack size and shape; the pipeline operating mode (running versus shut-in) during the leak; leak detection threshold of the existing leak detection system (if available); uncertainty in the measurement devices (flow meters, pressure transmitters, temperature transmitters, etc.); starting time (onset) of the leak as well as other factors. To complicate any leak volume analysis, there is a lack of documented procedures to determine the leak rate and the total released volume.
The purpose of this paper is to present methods that could be used to calculate the leak rate through the pipe hole/crack. Then, during the period that the pipeline was leaking, methods (both operating as well as shut-in) are presented to estimate the total released volume.
Two approaches namely “Equivalent Diameter” and “Hydraulic Diameter” are presented in this paper. Methods are presented for calculating the leak rate through irregular shapes from a simple hole to complicated cracks that will vary the leak rate as the crack can expand wider when subjected to pressure. Simulation results for accumulated released volume will also be provided in this paper. Results verified from an actual incident show that both Equivalent Diameter and Hydraulic Diameter approaches provide accurate estimations of the total released volume. The variation of the pipe crack opening area with respect to the pipe operating pressure will also be discussed in this paper.
There are many factors that can contribute to a pipeline leak. Examples of contributing factors for causing a leak are fatigue cracks, stress corrosion, hydrogen indexing, material manufacturing operator errors, errors in quality control of construction, age of the pipeline, operating pressure, elevation profile, external damage among others Although pipeline companies strive to prevent pipeline leaks through their integrity management (IM) program, incidents happen on pipelines that result in product released into the environment. Many pipeline operating companies include methods such as leak detection programs to reduce the consequences of a leak on a pipeline by speeding up the discovery of leaks.