question for lazy pup

[jocar]

In some of your older posts you stated that when hooking up a hot water tank instead of useing dielectric unions on the galvanized nipples, 6" brass nipples can be used instead.Could you post a diagram on how you would plumb the water heater using the brass nipples as I am not sure if you would remove the galvanized nipples and replace with the 6" brass nipples or leave them in place and use a galvanized threaded coupling screwed to the galv. nipple and then screw the brass nipple to the top side of the threaded coupling.

[LazyPup]

The pressure vessel inside the water heater is made of steel and the threaded ports are 3/4" FIP steel ports.

A nipple has an MIP thread on each end so you would screw one end of the nipple directly into the tank port and on the opposite end of the nipply you could use an FIP copper thread adapter to transition to copper, but be real careful here. Code says a "6 inch hardened bronze" nipple.

Most big box stores carry 6" brass nipples but they do not carry hardened bronze nipple.

Many guys have argued that you can use brass nipples but that is not correct. Many inspectors see a brass nipple and they will give you a pass for effort, but if you get a hardnosed inspector he/she will red tag your job, and some do not even tell you why.. They simply say "If you had a real plumber he would see it plain as the nose on your face" as they walk away.

[Nestor]

MIP = Male iron pipe thread, meaning externally threaded like a bolt
FIP = Female iron pipe thread, meaning internally threaded like a nut

Lazypup:
Can you post some reference or web site that confirms what you're saying about the nipple having to be bronze and not brass?

Cuz I keep getting web sites that tell me to use either bronze or brass, like this one:

AskCodeMan.com - Ask Codeman Building Code Q & A

but, I don't think he knows what he's talking about either cuz he says "steel is made with zinc" and, while I don't know how much zinc there is in steel, I'm confident that it's only a trace amount.

Also, the whole idea behind using a bronze nipple between the steel tank and the copper piping is to reduce the amount of galvanic corrosion that would occur between the two pairs of dissimilar metals, that is between the steel and the broze and between the bronze and the copper.

But, if you look at any galvanic chart, like this one:

http://www.corrosionist.com/Corros1.gif

http://www.hazmat-alternatives.com/images/Galvanic_Series_Chart.jpg

http://www.grabberman.com/Media/TechnicalData/127.pdf

you'll see that the galvanic potential of different kinds of brasses and bronzes are about the same, so you'd expect about the same amount of corrosion using a brass nipple as a bronze nipple.

So, why the need for a bronze nipple? What will happen if a brass nipple is used instead of a bronze nipple? (I mean besides the work failing the plumbing inspection, of course).

[jocar]

question for lazy pup

So you are saying to unscrew the galv. nipples from the tank and screw in the brass or bronze nipples in their place, am I reading you correctly?
Joe

[pushkins]

Yes, that is what he is saying.

[Nestor]

...and then at the other end of the bronze nipple, he's saying to use a copper FIP fitting, which looks just like this:



To make the transition from the threaded bronze nipple to soldered copper pipe.

But, three things here:

1. The bronze nipple needs to be at least 6 inches long.

2. Make sure those are just galvanized nipples you're removing and not heat traps. I've never seen a water heater come with factory installed nipples in it, so those might be heat traps. A heat trap is just a piece of pipe with either a polypropylene or nylon ball inside it. Since polypropylene floats, you screw the heat trap with the polypropylene ball into the cold water inlet port. Since nylon doesn't float, you screw the heat trap with the nylon ball into the hot water outlet port. Together, these heat traps prevent hot water inside the tank from convecting upward into the house's hot water supply piping, cooling, and sinking back into the water heater. And, of course, they prevent the cold water in the supply line from sinking into the water and hot water in the tank from convecting up into the cold water supply piping. That is, they prevent the free flow of water from the tank into the piping where it'll cool down faster.

3. This might be considered overkill, but if it wuz me, on your threaded connections, use teflon tape first, and then apply pipe dope onto the teflon tape. For galvanic corrosion to occur, one of the necessities is that the two dissimilar metals be in electrical contact. The better the electrical contact, the higher the rate at which corrosion CAN occur. By electrically insulating that threaded contact as much as possible, you strive to get the worst electrical contact you can between the bronze nipple and the steel tank and between the copper piping and the bronze nipple, thereby minimizing the amount of galvanic corrosion that can occur.

[HayZee518]

nipples

could the reason be that brass and bronze is an alloy of the base metal with a nickel additive making it compatible with the copper. electrically they are almost at the same potential reducing the galvanic action. brass or bronze is less active with steel as opposed to steel and copper.

[Nestor]

No, Hayzee, nothings ever easy.

I majored in metallurgy when I was in my undergraduate program, and there are lots of things that affect the properties of alloys, including one real important one, which is it's crystalline structure. The crystal structure of a metal or alloy affects the way it behaves in a lot of ways. And, just because both brass and bronze are made from copper, their crystal structures may be different.

Just the same way that wood is made of "cells", metals are made out of tiny "grains". And, each grain has a crystalline structure, meaning that all the metal atoms in that grain are all arranged in a regular and repeating pattern, just like the carbon atoms in a diamond.

When you let a molten metal cool, the metal will start solidifying in a lot of different places at once, and each "grain" or "crystal" will grow as a result of atoms precipitating out of the liquid metal and taking their place in the regular ordered arrangement of each crystal, or "grain". That is, metal grains grow just like snowflakes grow; by metal atoms or H2O molecules taking their place in a crystal structure. Each crystal keeps growing until it encounters (and interlocks with) other crystals.

The effect is similar to what happens when a collection of small towns grow and merge into one big city. Within each "town" or grain, all the streets and avenues will be perpendicular to one another and the streets will be oriented in one direction while the avenues will be perpendicular to the streets. The same thing happens in every grain or crystal or town, but the orientation of the streets and avenues are typically different in each grain or crystal or town.

So, when the towns grow and merge into one big city, there will be areas within that city where the streets and avenues are all straight and perpendicular, and other areas at the borders of the former towns where the streets and avenues will stop in dead ends, or change direction, or do something else, in order to better merge with the orientation of the streets and avenues of the neighboring town. Exactly the same thing happens when a metal cools from a liquid to a solid, but it occurs in three dimensions instead of just two.

Also, different kinds of metals have different kinds of crystalline structures. Think of that as one town having really long distances between the streets, but short distances between the avenues, or a town having two kinds of avenues, each at a 45 degree angle to the streets.

If you imagine a cube, some metals will have an atom at each corner of that imaginary cube. Other metals, like iron, will have an atom in the center of the cube AND one at each corner. Other metals, like nickel and chromium, have an atom in the middle of each face of the cube and one at each corner. Other metals have their atoms arranged in a hexagonal pattern instead of a cube, and others have the atoms arranged in the shape of a tetrahedron instead.

So, when you start mixing metals to make alloys, things can get ugly fast. The alloy you get will still be made of "grains" but the grains won't necessarily have the same crystal structure. If you do have the same crystal structure in all the grains, it might be that of one parent metal at low temperatures and that of a different parent metal at high temperatures. Or, the crystal structure can change abruptly from that of one parent metal to the other as you change the composition so that a small change in composition can result in significantly different behaviour of the alloy because of that change in it's crystal structure.

Metallurgists have phase diagrams that show the different crystal structures alloys will adopt as you change the temperature and the composition. The relatively simple phase diagram for iron with carbon in it (which is what steel and cast iron are) is shown below:

And, it's complicated enough.

So, no one really understands why alloys form the crystal structures they do, let alone why one alloy works well in one circumstance while a similar alloy (like brass and bronze) doesn't under those same conditions.

[mrcaptainbob]

Metallurgy class...

I took a Strength of Materials class many seasons ago. I loved it. But it was now where near informative as your post, Nestor. You sure are a positive addition to Home Repair Forum. Thank you very much for sharing your education with us. And for doing it in such an easy-to-understand way, too.

[Nestor]

If you're interested in the crystal structure formed by metals, this web site shows a periodic table with the kind of crystal structure each metal forms:

Periodic table (crystal structure) - Wikipedia, the free encyclopedia

On that periodic table, the different colours reflect the kind of crystalline structure each metal adopts. The number at the top of each metal is it's melting temperature. And the letters "bcc", "fcc" and "hcp" stand for body centered cubic, face centered cubic and hexagonal close packed.
The idea for including the melting point of the metal is that one would expect that the more stable the crystal structure adopted by a metal is, the higher the melting point of the metal.

But, except for some general observations made in the text of that web page, there doesn't seem to be any recognizable organization to that table so far as crystal structure goes, or any significant degree of correlation between the crystal structure and the melting point. If there was a way to arrange the metals so that there'd be some apparant rhyme or reason to why different kinds of metals will adopt different crystal structures, or have the melting points they do, the information on that periodic table would have been presented in that more understandable way. Instead, they post the data on the periodic table, and what you see is a hodge podge of different crystal structures and melting temperatures scattered all over the place. Maybe some day someone will be able to make sense of it. But it won't be today, and it certainly won't be me.

The body centered cubic and face center cubic structures were explained in my last post. The hexagonal close packed structure is where you have a hexagon with an atom at each corner AND one in the middle of the hexagon. Imagine a sheet of atoms with all of the atoms in that repeating hexagonal pattern. Now, if you have multiple sheets of atoms like that, what actually happens is that each 2nd sheet moves slightly so that each metal atom can fit into the recesses between the atoms of the first and third sheets, like this:



The second illustration shows that arrangement the best. So, each plane of atoms has the atoms arranged in a hexagon with an atom in the center of the hex, and each even numbered plane will have the atoms slightly shifted from each odd numbered plane so as to provide a denser packing arrangement of the atoms.

Also, I should note that I made several mistakes in that last post (cuz I was typing it from what I remember in university over 25 years ago now). I claimed that some metals have a simple cubic structure where there are simply atoms at the 8 corners of a cube, whereas in fact no metals have that structure. And, I said that chromium had a face centered cubic structure, whereas it actually has a body centered cubic structure according to that periodic table cited above. Going from memory after 25+ years, that's not too bad for an old man.

[mrcaptainbob]

Mistakes in posting....

Yeah, I saw those errors, Nestor, but didn't want to embarrass anyone by mentioning them....(pffft...yeah, right....) {