Page 48 - Pipeline Pigging Technology

Available on-line technology

WHICH TECHNOLOGY IS BEST?

The answer to this question has to be the same as it is for every other
industry when trying to select the best method for doing anything involving
an advanced technology:

"It depends...."

Most of the controversy has been concerned with the relative merits of the
advanced MFL and U/S tools as each vies with the other to gain a larger share
of the market. This competitiveness is certainly in the interests of the
operator, as it constantly drives the technology forward. However, the rate of
change makes open discussion of the subject somewhat risky, even for those
actively engaged in the development work, let alone for an impartial ob-
server...
By way of example, a paper presented by deRaad in 1986[5] gaveadetailed
comparison between MFL and U/S tools. Many of the points he made were
subsequently refuted in a paper by Braithwaite and Morgan [6] less than 18
months later.
There are one or two misconceptions which can, however, be removed:

advanced MFL is (essentially) not influenced by speed;
U/S tools are only influenced by speed to the extent that the impulse
frequency is fixed, so the speed will determine the distance between
readings;
advanced MFL is not affected by changes in wall thickness;
advanced MFL has limitations in the heavier wall thicknesses;
U/S has limitations in the lighter wall thicknesses.

Often the decision is made by asking the simple questions:

Am I prepared to have a liquid in my gas line?
Are the traps long enough to house the pig?
Is there a pig to suit the size of my line?

When there is no obvious answer, call in the suppliers - and talk to other
operators who have recent experience. There are plenty who have past

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