INCORPORATING COLD CHAIN
CONTRIBUTORS
All images supplied by Andrew Perks.
I can understand the undetected corrosion under insulation.
areas where pipework penetrates through walls and concrete roof slabs will always be suspect, the piping needs to be in a sleeve, and changes in direction at tees and elbow are seriously affected by expansion and contraction on long pipe lengths.
I suppose I can understand the undetected corrosion under insulation but what really does upset me is when I walk onto a site and the evident corrosion around condensers and other pipework that can only be classed as poor maintenance.
We are dealing with a hazardous medium: it’ s quite easy to keep it in the pipes, all it needs is a proper maintenance plan and to monitor that it is being done. That’ s why we do the three-yearly SANS 10147 plant audits. A plant that is tidy and clean always seems to work better.
The preparation of pipework prior to the application of the insulation is paramount to the longevity of the material. I once decommissioned an abattoir in Windhoek and the freezer pipe mains in one of the corridors was totally enclosed in ice. Well, there were two suction mains, one on each side of the corridor. Both circuits were decommissioned while one that had been painted with red oxide was totally corroded, the other was painted with bitumen and once the ice had defrosted it was as good as new, and we could have reused it. This is all about the preparation of the pipework when it’ s new.
The type of insulation being installed should be done in double layers where the joints are all covered by the second layer. The pie chart indicates where wet insulation is more susceptible with elbows, tees and valves being the more problematic, accounting for 85 % of moisture found trapped in insulation. With corrosion comes a wall thickness degradation. Overall, 51 % of systems investigated for the presentation exhibited pipe thickness wall loss of more than 30 %.
Not all corrosion will lead to the material being condemned. Whether to repair or replace will depend on the actual corrosion, is it now below an acceptable limit. What are the limits? There are different thoughts on this, best get an NDT thickness test and an
AIA’ s opinion.
At the end of the day, it comes down to introducing a rigorously controlled and monitored corrosion protection programme.
CLA
So just because there is no moisture or ice on the surface of the insulation doesn’ t mean there is none beneath.
Covered in ice.
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