Galvanized pipe brazing 3

[marker123]

Anyone has experience in brazing of galvanized pipe in fire system piping?
I'm interesting how this joint working during water hammer?

 

[11echo]

I wouldn't suggest brazing galvanized pipe! The fumes can make you very sick. Every fire water system I've run across that is galvanized has been threaded. Good Luck with your project! ...Mark

 

[Rich2001]

One of the alloys use to braze galvanized steel is 63% Cu, 37% Zn, 0.3% Si, 0.15% Sn. However, brazing is typically done on thin sheet material, where the gap at the joint is along 1/2 the sheet thickness, nowhere along the thickness of pipe used in fire sprinkler applications.

Brazing of Galvanized steel presents a few problems that are detrimental to pressurized applications. These joints can catastrophically fail resulting the in loss of life and property.

The brazing temperature approaches the melting point of the galvanizing. Depending on the galvanizing alloy the melting temperature may be as low as 830F. Brazing, oxy-fuel or inert gas torch brazing, being a relatively slow process, allows a significant amount of time for elements in the galvanizing alloy to migrate into the steel. This leads to Liquid Metal Embittlement of the steel. Galvanized chimney flue liners typically fail in the manner, numerous house fires have been reported due to this.

Brazing pipe together is highly depended on fit-up. Galvanize coating is not an exact science, the thickness can easily vary 0.3 mm. This results in poor wetting of the joint, during brazing.

Welds typically have porosity problems due to the volatility of zinc at welding temperature. Cracking is also a problem.

Either Welding or brazing may result in a failure with or without water hammering occuring.

 

[imok2]

Brazing Galvanized pipe can be done , but you must remove the galvanized coating in the area to be brazed. I have done this with silver solder and the proper flux, then you can cold galvanize the joint. For instance: say you want to braze 2 pipe ends togather..to remove the gal coating use a pipe cutter and cut small groves into the gal coating then you can chip off the coating and the groves will help the strength of the braze, take a non gal coupling, making sure it's very clean(no oil)and make it up!! So it't can be done BUT.. do not braze on galvenized coating fumes are very toxic!!!

 

[imok2]

P.S. We always used Victaulic couplings, they are very easy to work with and you can cut the pipe groves yourself.

 

[yogibear1]

In regard to Imok2 and the Victaulic system. Would you also recommend the use of a heavier (thicker) wall pipe to compensate for the groove causing a a localized pipe wall reduction? Wouldn't this be an important consideration for the pressure waves set up by water hammer?