SailNet Community banner

1 - 12 of 12 Posts

·
Super Moderator
Joined
·
6,773 Posts
Discussion Starter #1 (Edited)
Dezincification Photo

I hear the subject of dissimilar metals come up a lot and also the term dezincification. Lots of folks just go "huh?" when they hear that word. I've also heard others try to describe what to look for so here it is..
This is what dezincification actually looks like on a piece of brass. This is one of the end caps from my Westerbeke heat exchanger. You really need to clean the metal to see signs of dezincification.

Change your zincs regularly, especially in the engine zinc!!



Before:
 

·
Registered
Joined
·
270 Posts
what did you use to clean the brass? Also I have a yanmar 3jbh where would I look for zincs on the engine? I do not see any in the service manual. I do change the zinc on my prop shaft regularly.
 

·
Registered
Joined
·
5,607 Posts
This is from one of my seacocks. Note the salmon colored look, dezincification. You can see some gold speckles where I scraped through to the good bronze:

 

·
Member
Joined
·
124 Posts
dezincification is ?

Ok, so what is going on here? Dezincification to me would mean a loss of zinc, but we are talking about bronze are we not? Or is this some kind of transfer of zinc from the anode to the bronze part? I don't see how a piece of bronze could lose zinc. Or is the bronze losing tin. Then wouldn't it be deTINification? I'm not trying to be flip, just trying to understand what's going on with the metals.
 

·
moderate?
Joined
·
1,000 Posts
ambian...many of the engine manuals make no reference to a zinc as the manuals are not written for the marinized version of the basic engine. On the other hand...some marinized engines do NOT have zincs. My yanmar 4jh did not and perhaps yours does not either. The place to look is on the heat exchanger for a bolt head that looks like it is not holding one thing to another. Here is one example of a pencil zinc but they do come in other shapes and sizes.


Call Torrenson Marine if you want to be sure about your engine not needing one. Phone: 231-759-8596
 

·
Super Moderator
Joined
·
6,773 Posts
Discussion Starter #8
Ok, so what is going on here? Dezincification to me would mean a loss of zinc, but we are talking about bronze are we not? Or is this some kind of transfer of zinc from the anode to the bronze part? I don't see how a piece of bronze could lose zinc. Or is the bronze losing tin. Then wouldn't it be deTINification? I'm not trying to be flip, just trying to understand what's going on with the metals.

In my original post the end caps are brass though bronze can and often contain up to about 5% zinc. Dezincification is much more common in brass than bronze..
 

·
Registered
Joined
·
2,487 Posts
If that is bronze... and on a heat exchanger I suspect that it is... then what you are describing is destannification, a loss of tin. That characteristic pink colour would make me suspicious that you are losing tin, and loss of tin gives a characteristic pink hue, commonly seen in props.

Zinc is an awful material at the best of times.
 

·
Super Moderator
Joined
·
6,773 Posts
Discussion Starter #11
If that is bronze... and on a heat exchanger I suspect that it is... then what you are describing is destannification, a loss of tin. That characteristic pink colour would make me suspicious that you are losing tin, and loss of tin gives a characteristic pink hue, commonly seen in props.

Zinc is an awful material at the best of times.

No it is brass! Many, many HX's are made with copper, brass and red brass or bronze all in the same HX. Oh and lets not forget solder and stainless for the end cap bolts! There is a reason why they have a zinc..
 

·
Registered
Joined
·
825 Posts
Well these two pictures are of bronze.
The prop was half covered with propspeed. Of the rest about half looked like copper and half bronze with a bit silvery.

The other picture is of the prop retaining nut.
The outside was covered with propspeed. When tapped it fell to pieces, and the propspeed came off leaving the outside of the nut looking coppery but the inside black with only a tiny proportion of bronze colour. There is another part crack visible only on the top, but it looks like the nut was already cracked and barely held together.
 
1 - 12 of 12 Posts
Top