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 Recurrent pinhole leaks in hot water lines
Author: AusSn (TX)

House about 25 years old. Converted to tankless water heater about 6 years ago. Has a recirculating pump and recirculating loop.

Have had rare leaks before the tankless but a rapid escalation in pinhole leaks always in hot water line. Often times a significant distance from the heater and pump.

On a recent leak a plumber gave us a section of the pipe he replaced as shown below. Is this from bad installation and flux? Recirculating turbulence? Something else?

How do we know how much pipe to replace? Do some spot checks and cut into pipe? Replace it all? Cold lines too?

Thanks!



[www.dropbox.com]

(to see just click on dropbox's "decline" button)



Edited 4 times.

Post Reply

 Re: Recurrent pinhole leaks in hot water lines
Author: bernabeu (SC)

Assuming that your water is neither acid or too base (copper likes slightly alkaline water) the damage is DEFINATELY from erosion caused by:

non reamed copper tube in the fittings

and/or too high flow velocity (copper likes 2-3 feet per second, will 'accept' 4-5, but 6 and over is NFG)

? is there a properly installed flow restrictor union in the recirc line AFTER the pump ?



said union need be close to but after the pump and at the start of a long straight run of piping so no turbulence causes damage

Post Reply

 Re: Recurrent pinhole leaks in hot water lines
Author: AusSn (TX)

This is the pump. Not sure how to measure velocity though? I do not see the flow restrictor you describe near the pump.

With this much damage sounds more like the whole house's hot water needs to be replaced? How far away is the turbulance an issue?

Post Reply

 Re: Recurrent pinhole leaks in hot water lines
Author: bernabeu (SC)

There are MANY factors involved.

Water pH - copper likes slightly alkaline, if acidic then copper itself is nfg as material

Water velocity - undersized piping will cause excessive velocity / erosion

Improper installation - unreamed tubing ends

Type 'M' thinwalled tube used

Circulator pumps running 'full bore' and with UNrestricted flow


You need a LICENSED BONDED INSURED plumber with DESIGN knowledge on site


GOOD LUCK

Post Reply

 Re: Recurrent pinhole leaks in hot water lines
Author: packy (MA)

if berns numbers are correct about the flow rate (i'm not doubting he is correct, i just don't know anything about flow rates)
the 007 is moving water too fast. this is from their web site.
Flow Range (GPM):
0-23

Max Flow (GPM):
23

Post Reply

 Re: Recurrent pinhole leaks in hot water lines
Author: bernabeu (SC)

packy,

when i apprenticed the max recommended velocity for Cu tube was 6 AS PER THE COPPER TUBING INSTITUTE



there MUST be a flow restriction device AFTER the pump to limit velocity (2fps or less recommended)

HOWEVER

if the hw piping is uninsulated ????????????????????????

Post Reply

 Re: Recurrent pinhole leaks in hot water lines
Author: bernabeu (SC)

Water Velocity Limitations
To avoid excessive system noise and the possibility of erosion-corrosion, the designer should not exceed flow velocities of 8 feet per second for cold water and 5 feet per second in hot water up to approximately 140°F. In systems where water temperatures routinely exceed 140°F, lower flow velocities such as 2 to 3 feet per second should not be exceeded. In addition, where 1/2-inch and smaller tube sizes are used, to guard against localized high velocity turbulence due to possibly faulty workmanship (e.g. burrs at tube ends which were not properly reamed/deburred) or unusually numerous, abrupt changes in flow direction, lower velocities should be considered. Locally aggressive water conditions can combine with these two considerations to cause erosion-corrosion if system velocities are too high.


{Therefor a flow restrictor is required when a recirc pump is installed}


As per: Copper Tube Handbook lll [www.copper.org]

Post Reply

 Re: Recurrent pinhole leaks in hot water lines
Author: vic (CA)

I suspect B is onto the cause ... high velocity.

I've replaced a lot of type K copper pitted piping in commercial buildings (while working for the Los Angeles County Mechanical Department) that were determined that the copper was getting destroyed internally because of oversize circulating pumps which created constant too high/fast velocity.

Post Reply

 Re: Recurrent pinhole leaks in hot water lines
Author: bernabeu (SC)

vic & op

simple solution




juuuusst downstream of the circ pump and (preferably) upstream of a 10 pipe diameter minimum straight run

soooo .... if 1/2" cu then 5" min straight AFTER the restrictor, longer is better

Post Reply

 Re: Recurrent pinhole leaks in hot water lines
Author: vic (CA)

Once pitting has been noticed in copper piping, even with throttling down the velocity/speed of the water at that time inside the copper pipe most likely there already exists much internal pitting. Will more leaks show up? Hard to predict, certainly an issue.

Ideally circulating pumps are sized properly as well as depending on the situation I like to recommend having a timer or motion sensors to allow the pumps to not circulate water 24 hours a day to also save energy.

Post Reply

 Re: Recurrent pinhole leaks in hot water lines
Author: bernabeu (SC)

AND a flow restrictor so that when they DO run they do not 'induce' high velocity



TOMATO or TOMATOE



grinning smiley

Post Reply

 Re: Recurrent pinhole leaks in hot water lines
Author: ArthurPeabody (NM)

Could he switch to PEX?

Post Reply





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