Hot City Water Galvanized Pipe

[NCENG78]

I need to replace an older Hot City water piping system. Water is heated in a storage tank and piped to vessel jackets for heat. Temperature of the system is 75C. No treatment chemicas are added as this water is used for vessel cleaning. Its currently galvanized pipe. At previous sites we've used only stainless steel piping for untreated hot city water systems. There’s some severe corrosion on the inside of the pipe and many patch clamps. Any recommendations and justifications to convince my group to switch from galvanized to different material?

 

[LittleInch]

I think you've just made it. Aerated hot water will corrode steel quite quickly unless protected. Galvanisation is good, but any fault or erosion at any specific location such as a tee or elbow, can easily lead to a leak which will simply not happen in stainless tubing. 75C is probaly a bit hot for most non metallic piping of a decent size so you're really stuck with metallic pipe systems. If you could get some composition data or physical properties (pH, TDS, that sort of thing) you might be able to show corrosion rates in differnet materials, but i supose this varies with time.

Only you can see whether the additional cost is worth it in terms of reduced maintence costs / loss of heated fluid while you repair it or potential for injury due to hot water injuring personnel.

At the end its about confidence in your system and how much you want to pay for it.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[rconner]

You may be interested in the discussion of "polarity reversal" at

http://www.galvanizeit.org/images/uploads/drGalv/Polarity_Reversal_Galvanized_Steel.pdf?tracked=yes

, as well as the experience of the folks at e.g.

http://geoheat.oit.edu/pdf/tp125.pdf

over many decades with different kinds of piping materials for demanding geothermal application.

 

[moltenmetal]

Galvanized is marginal for fresh (aerated, open loop, untreated) water when it's this hot. Every galvanic connection will become a problem.

Copper typically lasts longer but its survival depends on water composition.

PEX lasts forever but is limited in size. 75 C is at but not beyond the limit of what PEX will handle.

Unless your pressure is very low, 75 C is beyond what I'd consider safe long term for CPVC. PP would work but is expensive because it requires thermal welding- it's popular in Europe but much less so in North America.

Austenitic stainless steels would be a good choice unless there's a lot of chloride, in which case you're looking at a lean duplex.