Corrosion of Aluminum and Brass in a waterhater

Question

Corrosion of Aluminum and Brass in a waterhater

GraySyracuse (Materials)

(OP)

12 Aug 03 07:31

Folks,
I have a question from one of my customers. They are building commercial/residential boilers and are interested if it is any possibility of reaction between brass and aluminum alloys or stainless steel, brass and aluminum alloys. The boiler body is made of aluminum and he wants to use brass couplings with SS sealants. Is anybody having any problems like this? Is anywhere I can find info about this?
I appreciate your fast response.
CC

Rich39 (Military) · Answer 1 · 2003-08-13 08:06:59

Initially I would have to say that a quick read of the galvanic scale would indicate large potentials between any of these materials. But in saying that I note that there is not much info with respect to pressures, temps, electric coil/gas/etc...... Are these real boilers or just water heaters (no steam)? More info would help but just from the material selection I would say not in those combinations. I know the USNs regulations on materials used in boiler construction is extremely strict so I would say that the civilian boiler code would be the place to go. I would also assume that if these 'boilers' are a pressure vessel then the certification will be required - or approval of the design specs/dwgs.

RC

GraySyracuse (Materials) · Answer 2 · 2003-08-13 09:33:43

RC,
Thank you for your fast response.
You are right; those are not "really" boilers, there are water heaters, using natural gas. I do not know what pressure could build into them.
I'll try to contact the customer to give me more info.
Regards,
CC

SimonJolley (Chemical) · Answer 3 · 2003-08-17 18:31:44

Hi, I had a project to put brass vales in high pressure aluminium gas cylinders. If there was no "neutral" interface between the 2 materials the vavle would "weld" itself to the aluminium. It would rip threads out or tear the top of the cylinder off when it was removed!
We had to fit PTFE or lead caps over the valve threads. PTFE tape worked sometimes but if you missed a bit it would weld.
I would advise you to be extremely careful with brass in Ali.

Simon

kenvlach (Materials) · Answer 4 · 2003-08-26 00:27:32

For hot water systems, dielectric pipe unions containing an insulating gasket are used to prevent galvanic corrosion in connections between brass and steel or iron.  Don't know if available in aluminum on one side; try a search or use a machine shop.  Also, look up the standards mentioned below.

Dielectric Pipe Unions
"Need to connect different metals in a piping or plumbing system? Use these unions to help prevent destructive electrolytic corrosion (electrical current generated between dissimilar metals that causes corrosion). Also good for connections that must be electrically insulated. Use for air, water, oil, natural gas, and gasoline. To assure a tight seal, these unions have a Buna-N gasket and Zytel 103 HSL insulator. Maximum temperature is 210° F. Max. pressure is 250 psi.
     Unions meet ANSI B16.39; ANSI B2.1, Class 1; ANSI B1.20.1; and Federal Specifications WWU-531E and WWU-516B.
Steel/iron-to-brass unions  1/2"-1" are carbon steel to brass; 1 1/4" is carbon steel to brass with galvanized malleable iron nut; 1 1/2"-2" are malleable iron to brass. Steel/iron-to-galvanized iron unions  1/2"-1" are carbon steel to galvanized carbon steel; 1 1/4" is carbon steel to galvanized carbon steel with galvanized malleable iron nut; 1 1/2"-2" are malleable iron to galvanized malleable iron.
     Connections: NPT female on both ends (unless noted)."

--from McMaster-Carr (http://www.mcmaster.com/)

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Corrosion of Aluminum and Brass in a waterhater