Closed CHW loop solder joint leaks

[ChasBean1]

Have a Closed loop chilled water system, several solder joint failures resulting in leaks. Joints I'm pretty sure are typical lead free pipe solder. 30% propylene glycol solution.

Water chemistry sample:
pH: 11.00
Conductivity: 5,900 umhos/cm
Total Alkalinity: 15,000 mg/L as CaCO3
Calcium: below reporting limit
Total Hardness: 3.0 mg/L

My thoughts: pH seems high, but doesn't seem high enough to eat solder, although I'm not sure how solder interacts with propylene glycol and high pH solutions. Conductivity and Total Alkalinity are very high - for closed loops I'd think conductivity would be <1,000 or so.

Tried this post in the Chem. Eng. forum but no luck yet. Your thoughts/experiences are appreciated! CB

 

[RossABQ]

That does seem to be a high pH, but could be at the top of control range. What are the make-up water properties? (What was it filled with?)

How long has the system been in service? Have you examined the failed joints to see what the mode of failure was?

On a recent project, we had a 25% failure rate on joints in a copper air system with lead-free joints. One of the fitters could not get a good joint reliably. We cut open half his joints, and most had < 50% solder coverage. All the failures happened within days, tho.

 

[ChasBean1]

Ross, thanks for the response. Makeup water is typ. city water for the area - used for hundreds of other closed loop systems. Been in service for a couple months now. If there is a next leak, we are going to remove the joint and analyze it instead of re-sweating it as has been done for others. It could be workmanship...

 

[RossABQ]

Several of our clients have changed their specs to require brazed copper joints on all but trivial systems, and required that the fitters/plumbers qualify much like welders for those joints. It tends to weed out the low skill players. I have to admit, on home projects I've struggled to get solid joints with lead-free.

 

[berkshire]

ChasBean,
I just put a response in the Chemical engineering section.
I did not, realise you had cross posted, and I just came across this post, after I had responded to the other one.
B.E.

 

[DrRTU]

This sounds like poor workmanship. I would look into the solder, flux, and mechanical method used to clean the piping. A visual of the joints tells alot about the workmanship. I perfer a brazed joint on my CW and HW systems but have not had problems with numerous stay-brite & stay-brite #8 installations. On mains (GT 1") and vibration areas we switch to dynaflow brazed joints.

http://www.harrisproductsgroup.com/consumables/msds.asp#SOLDER