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There was probably a reason for pump coming with three inch flange on suction side. May need to run three inch line to boiler and reduce at boiler to 2 1/2” to stop cavitation. Most every fluid pump needs a larger suction than discharge line. May also be wise to use dielectric union at pump in case of electrolysis.

HC, have not done that, will check tommorow

It does resemble a stress fracture along a seam, perhaps with chemical compromising (accelerated damage) (pitting) caused by the product being pumped. If it were cavitation alone, I don't think there would be chemical residue.

Is the setting properly supported? Does this section need a flexible joint? Is the pump overated for the job at hand? If the pump is overated, then a recirc line would be needed to accomodate the flow requirements at low load. Just my initial thoughts.

Nice photo display!

There is also that threaded fitting downstream which might have incurred alot of twisting torque during assembly, which if so, could have stressed the tubing.

Can you get a long radius fitting?

I had a great article on this topic at one time that wasn't ever saved digitally so it's history.

There was a top notch boiler company that had installed a a unit in a older apartment building. They rotted the tubes out of the boiler inside of two years, twice.

They became aware they were facing a electrolysis issue but couldn't pin down the source.

Dielectric fittings (which I don't see in your images?) were not preventing their problem.

To make a long story short, they found that over many years of DIY'er type of electrical maintenance throughout the building the neutral lead had been bonded to the ground lead in many locations including sub panels and even some electrical outlets.

Bonding of ground and neutral leads can only be done at 'first strike'.
Which typically means at the main service feeding a structure and never again after that point or electrolysis is likely to occur.

Grounding rules and regulation make up the bulk of the NEC code book and the specifics bewilders MOST electricians. I've quizzed many life long electrical Journeymen and Administrators on the specifics of proper grounding of industrial equipment and steel buildings and sent them all to their NEC code book digging for answers.

Most electrical systems have grounds bonded to the water mains feeding a structure, right at those pumps is a likely location for electrolysis to occur.

It's interesting that it 'appears' your issue is limited to the one unit.
If that's truly the case you may find your problem local on that boiler, but that's rather wishful thinking.

What I would do immediately would be to ground the living schit out of the boilers chassis. I'd run some heavy copper (4/0) to a dedicated ground rod, or two. Find a good location on the boiler to bond to and grind the pretty paint off that brand new boiler and get a solid bonding point. De-ox the connections well.

It sucks that this isn't nessarally a plumber's problem but could very well be the plumber's problem to prove.

If grounding the unit corrects the issue I'd recommend, in writing, for the school to have a electrical contractor do some forensics work and locate the source of the problem or atleast have both boilers grounded with a cad weld grounding system so it can never be removed.
It is a kids swimming pool with a potential unknown electrical problem.

But that's just my two cents worth, what'da I know, I'm not even a electrician...

That could be very difficult to get a proper reading.
If it's the ground that is carrying voltage what would you connect the negative lead of your meter to?

Thanks SC... some thoughts in reply
If it were steel pipe I’d assume a weak seam of sorts as well but we’re dealing with copper here. What are you referring to specifically by chemical reside? If you mean the green tint yes these lines are pumping chlorinated water and I know that’s not helping the situation..
The assembly is supported with hanging bracket up top and strut bracing below. The whole assembly was soldered up and slipped into place with no stress incurred.

I can only assume the pump is properly sized for the job as it is sold to us a package by the boiler company who installs and warranties the same setups...
However I will call and ask why the supplies pump/flanges are 3” when boiler is 2 1/2 as that makes no sense to me.

JeffA.. some good ideas there thank you
You nailed it that it seems to be a problem in my lap!

I will look into how/if this boiler is grounded. I “think” there is a grounding strap coming off the backside but how what where it goes I can’t recall

You are also correct in that it only “appears” this is isolated. Without cutting the other boiler lines open I can’t be sure. The only thing I can be sure of is these lines have failed twice and the other has not.

I suspect there is at least a contributing issue with the volute/impeller being imperfect and causing cavitation and flow issues...
I was told the pump seal had failed a while back (less than a year old) and the impeller was in bad shape and replaced as well at that time. I heard the impeller housing was not in great shape and getting the new impeller in was “tricky”.
Obviously that’s not good..

I'd pull impedance from the area in question to a known ground. I'd check ac voltage from the same.

Then I would go across the piping on both sides of the pump with impedance.

My facility is littered with rotten copper. I've chased down most of the ac bleeds and cavitation.

HC..I’m on board with what you’re saying, but I just don’t know how to do it..
Can you walk me thru (plumber) specifically how I would check
These things with my meter

“go across the piping on both sides of the pump with impedance” .....mostly this part
Thanks

The things a guy can learn on here. . I know fugkall about the topic at hand but it’s an interesting read.

No schidt!

I've been a plumber for quite a while, but have limited experience with boilers. Mostly I just pipe them up according to the design, so keep that in mind when I say this; I thought it was commonly accepted that "pumping away" (there's an article on this by the same name) from a boiler was the preferred way, as it kept turbulence inside the boiler and the various devices, (low water limit, etc) located near the boiler, to a minimum.

Same piece of copper , from the same stick for the 2nd go around?

What I'm seen of boilers, they are a pain.

Suction side of pump or discharge ? Chlorine and Copper usually not a good combo in most Water treatment feed lines I have been around most were Schedule 80 PVC with glues that rated for chlorine. Looks like cavitaion to me the 90 is not helping. Just a guess. If its disharge on the pump any air bleeds installed?

Was the 90 ell replaced both times or not all all? You reaming all cuts?

Any chance a gob of solder or a burr from the cut was left behind?

That's erosion from some source that close to the ell.

If it was electrolysis or chemical, It would be appearing in other areas also.

You and I seem to be in the same boat, and yes your pumping away logic makes sense to me