(Another quick post. I still intend to continue the series on location classification but it might be a while yet.)
As I talk to pipeline engineers in different operating companies I frequently encounter misunderstanding about the significance of external loads on pipelines, such when someone wants to drive a heavy vehicle over the line. In fact the misunderstanding seemed to be so widespread that in late 2009 I decided it would be a good topic for a talk at a POG Seminar (Pipeline Operators Group). For various reasons it wasn’t an appropriate topic for the 2010 seminar but at the 2011 seminar last week I finally got to give the talk. So this has had a long gestation.
The essence of my message was this:
Do external loads matter?
Won’t cause failure (loss of containment)
- Except in truly extreme circumstances
- Worst case might be ovalling (pigging problems)
- May cause fatigue if repeated very often
Don’t solve a problem that might not exist
- May create unnecessary difficulty for both pipeline operator and third parties
- Installing unnecessary protection may increase risk
A PDF version of the full presentation is here. It includes a number of example calculations that show the very minor contribution to total stress from even large external loads.
I certainly don’t want to trivialise issues around external loads. But I think it is important that pipeline engineers have a proper understanding of what’s important. Don’t assume the worst – do the calculations. They are well-defined in API RP 1102 (referenced by AS 2885.1) and they are not hard.