Integrating Leak Detection and Custody Transfer for Pipeline Monitoring

by | May 12, 2016 | Industry, Measurement Instrumentation, Oil & Gas | 0 comments

Emerson's Rossella Mimmi

Emerson's Marc Buttler

Authors: Rossella Mimmi and Marc Buttler

The importance of pipeline integrity is growing in the oil and gas industry. New regions of oil and gas production and growing demand are driving the construction of new pipelines and reversals of existing pipelines. Older pipeline systems are still in operation and often running at capacity. 41% of US oil pipelines were built in the 1950s and 1960s.

A report that was prepared for the Interstate Natural Gas Association of America in 2012 indicated that there are even pipelines that were installed prior to 1920 (nearly 100 years ago) that are still active. Pipelines can be operated safely with a long lifetime as long as proper maintenance, operation, and inspection practices are employed.

Valuable Natural Gas Liquids (NGLs) with high Reid Vapor Pressure (RVP) are being transported at higher volumes than ever. This often results in the need to comply with regulatory requirements that were not applicable before. In order to comply with these requirements, there is a greater need than ever before for qualified personnel to operate, monitor, document, and maintain the pipeline and the aging infrastructure.

Regulatory requirements aside, it’s important to consider the huge impact of a leak, in terms of personnel safety, clean-up costs, civil penalties, loss of product and revenue for the shutdown of the pipeline, and the risk of damaging the environment. As an example, a California pipeline leak of 143,000 gallons of crude oil in 2015 will cost at least $250M in clean-up and other costs. It is estimated that clean-up of a typical pipeline spill will cost between $10,000 and $100,000 USD, depending on whether the spill is on dry land or near water.

Leak-Detection-SolutionsLeak Detection Systems (LDS) are of paramount importance to give operators the tools they need to ensure pipeline integrity and have the confidence they need that even small leaks will be quickly detected. There are several types of LDS, internally or externally based, depending on the measured characteristics. Some examples of external methods are line patrol and hydrocarbon sensing via fiber optic, dielectric cables etc.

Even satellite surveillance is used in some cases. In-line inspection (ILI) tools, such as smart pigs, can detect irregularities in the pipeline like corrosion, cracks, or deformations. Internal methods are based on the hydraulic characteristics of the product flowing inside the pipeline: pressure, temperature, density, viscosity and flow rate. Examples of internally based systems are:

  • Mass/volume balance
  • Real Time Transient Model (RTTM)
  • Acoustic pressure wave analysis
  • Statistical method

These systems have different characteristics in terms of reliability, sensitivity, accuracy and, of course, complexity and cost. More than one system can be applied for a higher level of security and back-up protection. In addition to the LDS itself, other modules can be added such as:

  • Training simulators, to ensure operator competency and confidence
  • Performance analyzers for sustainable performance
  • Schedulers for managing traffic

RTTM represents one of the more sophisticated and widely used leak detection methods. It gives high confidence to the customer on the ability to detect very small leaks and their location. It uses physical laws like the conservation of mass (like the balancing method), momentum and energy. It compares measured data for a segment of pipeline with the predicted conditions from the model:

  • Calculated pressure-flow profile of the pipeline overlapped onto the actual data profile
  • An intersection of the profiles indicates a potential leak and provides the location

The ability of RTTM to detect small leaks and their position (and to do it quickly) is heavily dependent on the accuracy and stability of the flow, pressure, and temperature instrumentation.

The role of Custody Transfer meters

Flow rate is a fundamental measurement input for RTTM, so flow meters have a very important role. It is no surprise that custody transfer meters can also offer the best performance for RTTM. The size of the minimum detectable leak, correspondent to the system sensitivity, is a function of the flow meters accuracies and output resolutions: the higher the meter accuracy, the smaller is the leak that can be detected.

Another important meter characteristic is stability, especially in liquid pipelines that move different products: when product batches and/or flow rates are changed, it is important to avoid false alarms from the LDS, so the meter must guarantee stability of the meter factor under changing process conditions. This is also important to minimize ongoing proving and calibration costs of the meters.

Emerson’s Micro Motion Coriolis meters have all the characteristics needed to perform exceptionally well in any LDS, in terms of high accuracy for all types of fluid, measurement stability, reduced maintenance and calibration operations that result in lower operating costs. Moreover, for liquid pipelines, the density measurement gives the oil & gas producer the added benefit of precision interface detection, enabling them to make improvements to product cuts that reduce the amount of slop that needs to be reprocessed.

For all these reasons, Coriolis meters are widely used by the most sophisticated LDS.

While the LDS software is of paramount importance to have efficient and effective leak detection, it’s not the only element. No matter how good the software is or whose software you are using, leak detection requires accurate and reliable mass flow measurement technology to work properly. The best software in the world cannot solve the problem of a poor and unstable flow measurement device.

Leak detection is a critical component of your overall pipeline management strategy. Contact Emerson for a complete solution for LDS; software, custody transfer meters, and instrumentation to help you assure your pipeline integrity.

From Jim: You can connect and interact with other oil and gas industry and flow experts in the Oil & Gas and Flow groups in the Emerson Exchange 365 community.

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The opinions expressed here are the personal opinions of the authors. Content published here is not read or approved by Emerson before it is posted and does not necessarily represent the views and opinions of Emerson.

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