EHT and galvanised pipe 1

[nipra03]

Hi,
I have a consultant who advises against using EHT (electric heat tracing) on galvanised pipe for firewater purposes on the ground that the localised heating can deteriorate the internal coating, cause clogging & premature corrosion failure of the pipe.
I am unconvinced that the problem is actually so severe that we have move away from using galv. pipe.
Any feedback ?

 

[gr2vessels]

Galvanised piping temperature limit is 200 deg C. Since I don't believe you boil the fire water in the pipe, your tracing should be OK at preventing freezing the water in the pipe, but not heating. Hot water and galvanised pipe is no mix. This also applies for unintended localised overheating due to tracing imperfections. Keeping the fire water temperature below 10-15 deg C (above 4 deg C) is OK, provided you inspect closely the tracing work.
Can you also ask the consultant for references to his advice? Perhaps he knows a bit more of your piping conditions than you disclosed us in your post.
Cheers,
gr2vessels

 

[nipra03]

thanks gr2 !
appreciate your feedback.

 

[bimr]

Heat tracing for freezing applications typically use self limiting heating cables that are usually designed for less than 150 F temperature.

 

[rconner]

​If one does a quick web search e.g. with keywords e.g.

https://www.google.com/?gws_rd=ssl#q=internal+buildup+galvanized+fire+water+pipe​

, I think one would find that non-cementlined steel pipes (galvanized in some fashion or not) at least in some water services are really no strangers to internal corrosion/tuberculation or "buildups". As to the influence of applied heat application, I guess at least due to Arrhenius effects etc that extra heat likely doesn't help.
Beyond that, I'm not exactly sure where the consultant may be coming from, other than I believe there is even a school of thought (I believe some disputed by the galvanizers) that there can actually be a reversal of polarity in the galvanic protection at lesser temperatures in some exposures. Again one could find information on this with a good web search and these keywords. All have a good weekend.