Water to Water Heat Exchanger Tube Failures

[Khacker]

I am currently trying to assist an owner with determing the reason for the continued failure of their domestic hot water heat exchangers. These are U-tube and bundle type HX's with the primary heating hot water circulating outside the tube bundle in the jacket. The tubes on the domestic water side of the HX's are erroding and pitting within 2" of the entry side of the tube sheet on the tubes. From the reading I have done it sounds like it could be an Erosion-Corrison failure. The domestic water is well water that is softened. We had circuit setters installed on the domestic side of each HX so we could measure the flow rate entering the HX's. They all seem to be within specifications both in flow (gpm) and velocity (approximately 6 fps). A friend of mine mentioned that if the cold water supply is connected to the entering side of the HX, it could be subjected to severe thermal shock. He also suggested that if indeed, high velocity within the tubes was the problem that more than likely you would have other failures throughout the tube bundles, particulary on the U-bends. Can anybody offer me any insight or point me in the right direction

 

[ChaChaMan]

Thinking out loud. You mentioned well water....could there be sulphur in the water, thereby making it acidic anc causing corrosion ?

 

[ione]

Your chances of getting valid answers will increase if you post this in corrosion engineering forum

http://www.eng-tips.com/threadminder.cfm?pid=338

 

[TJOrlowski]

Looks like a standard 8" 4-pass layout.

If the top left quadrant of tube holes is the inlet, is that the only place that the tubes are failing? Or are tubes failing all over the place?

Material of the tube sheet? Material of the tubes? Wall thickness of the tubes? How thick is that tube sheet? Is the unit a single wall, or double wall (leak detector) tube bundle?

Is the owner starting up, shutting down, and operating the unit IAW the manufacturer's IOM? Does the owner periodically flush or clean the bundle, or have any PMI? How long after installation of a new tube bundle is the unit leaking?

-TJ Orlowski