ABSTRACT:

This paper explores the ability of detecting a leak during shut-in conditions for both long and short sections of liquid phase pipelines, using the API 1149 report as a basis. The presentation will begin by briefly introducing the API 1149 report, describing a simple mathematical model for predicting temperature and pressure changes with instrument uncertainties during the shut-in process, followed by application case studies with leak and no leak conditions. The results will be examined with regard to providing recommendations for leak sensitivity.

INTRODUCTION

The API 1149 Report [1] provides guidance for predicting leak detection thresholds for a flowing pipeline. In reality, steady state conditions are not typically the case with shut-in pipelines due to the pressure change over time being a direct function of continually changing temperature. Additionally, uninsulated above ground pipe station yard piping can result in fluid pressure being a direct function of the ambient diurnal temperature variation. The API 1149 Report threshold determination is fundamentally based on the propagation of uncertainty principle; in contrast this paper offers an alternative solution to precision or random uncertainty estimation by exploring the more significant effect where the measured pressure change does not keep balance with the modeled temperature change. This paper begins by describing API 1149 report briefly, along with some limitations and then a formal foundation is made for shut-in pipeline simulation. Comparisons are made with the simulation results and an example API 1149 calculation. Overall, focus is placed on theoretical aspects which are typically performed on pipelines not-yet-in service in an attempt to provide some initial expectation for leak detectability.

API 1149 Overview

The API 1149 Report provides a very methodical approach for determining theoretical mass-balance leak detection sensitivity for any liquid phase refined products or crude oil pipeline.

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