The previous post gathered a number of helpful responses from experienced industry people. But before getting to the technical responses there is an interesting sub-text to this topic, relevant to everyone in the pipeline industry. None of the following is intended to be critical of the current operator, quite the contrary – they have recognised a problem from the past and are working to resolve it.
It seems likely that somewhere in the 30 year history of this pipeline there has been a loss of important documentation (i.e. details of the lining, appropriate procedures for pigging). Like many pipelines it may have been through several ownership/management changes over its life and would not be the only pipeline to have lost records.
I once came across a pipeline for which the new owner’s bean-counters had decided not to incur the storage cost for any documents older than 7 years (the tax office rule). But the as-built documentation was older than that …
Of course the importance of keeping construction and maintenance documentation should be blindingly obvious, until it isn’t and something like this happens.
To the technical nitty-gritty about pigging a lined pipe:
- There was a general consensus that wire brush pigging a lined pipe is not a good idea (no surprise there).
- Lining damage may be indicated by epoxy flakes or dust found in debris from past pig runs, if there are relevant records or access to people who were involved at the time.
- Whether lining damage matters depends on the purpose of the lining, which we don’t know. Lining is most commonly provided to reduce friction factor (increase flow and/or reduce pump/compressor cost). A flow lining which has been badly scratched is probably ineffective.
- Flow analysis may permit back-calculation of friction factor and hence internal roughness of the pipe; there would be a lot of subtleties in the analysis, it would have to use transient flow modelling (unless the flow is perfectly steady), and may or may not be sufficiently precise to reach a clear conclusion.
- Finally (and pedantically) to be strictly correct the lining is most unlikely to be FBE (Fusion Bonded Epoxy) – almost certainly liquid-applied epoxy.
On the basis of available information, we can’t say whether or not the existing lining has been damaged, but if the original reasons for lining the pipeline are still relevant and additional pigging runs are now needed, then the use of nylon brushes seems justified.