Galvanic Corrosion in 303, 304, 316 Steel 1

[Jack Benson]

Hello,

We are developing a heat recovery device for domestic hot water (grey water not black water).

The heat exchanger is made of 304 steel.

At the moment, we use PVC connections to the 2 inlets / 2 outlets to ensure there is no contact with copper or brass fittings.

I would like to change some of these to steel parts. They can be 303, 304 or 316 steel.

The reason for the PVC connectors connected to the heat exchanger is to prevent galvanic corrosion.

Is there any risk of galvanic corrosion if we connect this flexible steel tube directly to the heat exchanger:

https://www.coditherm.com/produits/flexible/flexible-extensible/flexible-extensible

(I work for a French start up - your browser should translate).

Other fittings I have seen contain 316 or 316L steel. Would these be suitable?

Does the L (Low Carbon) change the risk of experiencing galvanic corrosion?

I have seen tables such as this:

http://www.npfasteners.com/technical/galvanic-corrosion.htm

I have also read this thread:

https://www.eng-tips.com/viewthread.cfm?qid=88097

Any help would be appreciated.

thank-you

Jack

 

[MintJulep]

That just looks like organic sludge that builds up on gray water lines.

Have you never had to clean a sink or shower drain?

 

[Jack Benson]

if its just organic sludge then its not an issue. ty

i was not sure if it was just dirt or something else.

 

[Jack Benson]

I have just received the Milwaukee MW806 MAX 4-in-1 pH/EC/TDS/Temp. Combo Meter with ATC.

I need to run the calibration, but out the box my tap water as the following:

0.52 mS/cm
0.26 g/L
7.77 pH

thank-you

 

[Jack Benson]

I have come across textile braided flexible hoses that I can put an SS304 connector at one end and a brass connector at the other end. There is no metal in the braid.

This seems like a good solution for a dielectric electric fitting.

The hoses are rated at 10 bar, with burst pressure up to 27 bar.

I have only experience with steel braided flexible hoses.

Are known issues with textile braided hoses?

 

[EdStainless]

I have used hoses with aramid fiber over-braid.
They are more susceptible to abrasion so make sure that they don't rub against things.
They are also more limited in temperature range.
We used them where we had serious external corrosion issues.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

 

[Jack Benson]

Why don't steel braided hoses with nickel plated brass connectors suffer from Galvanic corrosion?

They are very common and widely used.

Is it because both ends of the hose (which are in contact with the potable water) are the same material (nickel plated brass)?

therefore, the fact that the braid that creates the electrical connection between them is stainless steel is irrelevant because the stainless steel does not touch the water - is that why there is no corrosion?

if there was a SS304 connector at one and and a nickel plated brass connector at the other end, with an EPDM hose in the middle, and there was a steel braid making an electrical connection, would there be a risk of galvanic corrosion?



I have just seen this on Wikipedia:

https://en.wikipedia.org/wiki/Galvanic_corrosion

It is suggesting that if a section of metal pipe had a plastic lining, even if there was no break in the electrical connection - it would prevent galvanic corrosion. Have i understood it correctly?