Myths of Large Diameter Leak Detection

trunk main leak detection

The following misunderstandings and myths are frequently encountered on why trunk main leak detection inspections are not required:

  • Our trunk main pipelines don’t leak
  • Our losses are less than 5% – we have bigger problems to worry about
  • You will see it immediately when a trunk main leaks
  • We perform regular above-ground inspections
  • We use conventional leak detection methods

With a local inspection database fast approaching 2,000 km of large diameter inspections, coupled with an additional 10,000 km of international experience performed by our North American based licensor (Pure Technologies), the above myths are easily refuted.

Leak Frequency
Internationally, we are seeing average leak frequencies on trunk mains varying from as high as 150 leaks per 100 km (i.e. 1.5 leak/km) in the United Kingdom to 23 leaks / 100 km in South Africa. This implies that for every 4 km of bulk pipelines in South Africa, a minimum of one (1) leak can be expected.

Leakage Rates
Real-time leak sizing is by no means an exact science and leak sizes are affected by several factors including operating pressure, leak geometry and physical dimensions, type and consistency of bedding material etc.

The pressure range we most often encounter in large diameter critical trunk mains varying between 5 and 25 bar. What is evident is that it does not take a big hole (i.e. 7 mm) at a low operating pressure of 10 bar to lose 100 kilolitres per day (35 Ml/year)! Also, at the same 10 bar operating pressure, a slightly larger 10 mm hole will lose 200 kilolitres/day (70 Ml/year).

Typical leakage rates seem to vary from as little as 10 kL/day to over 225 kL/day. From experience, a minimum daily leakage rate of 150 kL/day is used locally (55 ML/year). As we know, most leaks go undetected for years and unless pro-active leak detection inspections are carried out, will go undetected indefinitely.

Originally posted on LinkedIn on 25 October 2017 and was taken from a newsletter of South African bulk water pipelines specialist, SSIS Pipeline Services.

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