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Content archived on 2022-12-27

LEAK DETECTION OF OIL PIPELINES BY MEANS OF AN ACOUSTIC METHOD

Objective

The purpose of the project is to develop a measuring process and a measuring instrument for the continuous leak detection of pipelines.
At the present state of art many accurate and sophisticated instruments are available for measuring flow-rates, densities, pressures and temperatures. However no device exists for the measure and the continuous mnonitoring of the pressure wave celerity in the pipeline.
The purpose of this research - i.e. proving the feasibility of the proposed pressure wave celerity measurement and providing indications for future "in situ" experiments, has been fulfilled.
This work should be continued in two ways :
- as suggested in description of task 2, full assessment of the theoretical models developed in phase I and exploration of all their potentialities in order to have a reliable and valuable tool for further design of the real measuring devices;
- preparation and realization of a first pressure wave celerity measurement on an existing pipeline.
The idea of the present work was to study, to test and to develop an instrumentation suitable to be installed on pipelines and which is capable of detecting on continuous having a length of some kilometers.
This hardware can be installed at several locations on the pipeline (for instance where pressure and temperature measures are taken) and its outputs could be transmitted by SCADA to the supervisory computer.
In this way a leak detection program would enable to compute the inventory changes with much more accuracy than made so far.
Actually, if we consider a theoretical steady condition the continuity equation is : Q1 - Q2 = q2 and the problem of detecting a leak is confined to the one of measuring with suitable accurancy the flow-rates. Unfortunately transients occur quite often in most pipelines and even a non-severe transient may result in a sensible change of inventory. Therefore the capability of computing these changes becomes an important feature for a leak detection system in order to fulfill the following objectives :
a) maintaining an acceptable level of accuracy in presence of transients
b) adjusting the alarm threshold according to the amount of the inventory change being detected, i.e. to the consequent lack of accuracy.
The above is valid for both liquid and gqs pipelines.! This work was however addressed to the development of a technique intended for liquid pipelines. In this case it is useful to refer to the liquid volumes at reference conditions for accounting the flow-rates and the inventory.
The reference conditions usually are 1 Atmosphere pressure and 15 deg. C. temperature.
The causes for change of the pipeline inventory are substantially the two following :
1) change of the pressure profile, which results in an inventory change depending on the combined elasticities of the liquid and of the pipe;
2) change of the temperature profile, which results in an inventory change depending on the combined thermal expansions of the liquid andof the pipe.
The determination of the inventory changes due to pressure transients is usually achieved using a certain number of pressure measurements taken along the pipeline and running a computer model to build up the complete pressure profile basing on those measures.
Various computer models are available, but all of them operate integrating the waves differential equations for liquid flow in a pipe.

Call for proposal

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Coordinator

Polyconsult Servizi Srl
EU contribution
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Address
Via del Teatro 8
61032 Fano Pesaro
Italy

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