What is black iron?

A. Hi, Vinu. It is not possible to say what a term like "black iron" means out of context because it is not a specification but merely slang used as a shortcut. But because you are with a water utility, I'll assume you are referring to "black iron pipe". In this context, 'black iron' is just slang referring to steel pipe with black paint on it or no paint on it as opposed to being galvanized.

As the son of a plumber from before the age of plastic pipe, "black iron" was used on gas pipes (and often still is), whereas galvanized piping was used on waste piping.

A. It is my understanding that black iron is also called "black rust" as opposed to red rust. The black rust is much less "fluffy" than red rust. That is, red rust will allow oxygen and moisture to permeate to the surface and allows the progression of corrosion. The black rust is a protective oxide layer that helps block any progressive corrosion. This is sometimes referred to as a conversion coat. The black rust is ferrous oxide whereas the red rust is ferric oxide.

A. The context I heard it in is the manufacture of ferrous sulphate ferrous sulphate [affil links]. We were looking at potential markets for it.

A. I've seen the term 'black iron' for cookware at www.dissco.co.nz/products.htm
They refer to 'deep spun cold roll steel' as black iron.
Maybe that's of help to you?

A. I've seen both used, Richard, and they both seem okay. I'd guess that a high temperature paint [affil links] is better for high temperatures than galvanizing though.

A. Hi, Dean. I believe you are thinking of hot rolled low carbon steel sheet/plate, available from steel supply houses like Ryerson. Good luck.

Regards,

A. Black iron in the true sense really means wrought and tempered iron.

It may be in all its forms - plain wrought (as in kitchenware), faggoted iron (originally referred to as "Best", "Best Best" (for faggoted twice) and "Triple Best" (for faggoted three times).

It may be hardened or unhardened, so the term is very generic, usually to differentiate from cast iron.

The term is also erroneously used to refer to Ductile Iron or Low Carbon Steel, but it is not the same thing.

A. Hi, Rosalie. All three terms are slang rather than specifications, so the point may be moot anyway. But I think that I would use the term "mild steel" or "mild carbon steel" because the term "black iron" is actually inaccurate as Ron has mentioned, and some "carbon steel" is not mild whereas black iron pipe probably is mild.

Regards,

A. Hi, Aaron.

I believe you simply specify it as black iron pipe by size and wall thickness, like this: 2" NPS (nominal pipe size) Sch. 80 black iron pipe. But note that a 2" NPS pipe is neither 2" I.D. nor 2" O.D. :-)

Regards,

A. From what I found out today, there is no such thing as black iron pipe. If you call a steel house and asked for black iron pipe you get seam welded steel pipe painted black and it is hard to thread. If you go to a plumbing supplier and ask for black iron pipe you get ductile iron pipe, which is gray and easy to thread. Steel pipe can be used for some pressure application and as structural members. Black iron pipe is only for pressure not for structural. Personally I don't know how you can call steel pipe black iron, just confusing everyone.

Hi, Steven. You're right that steel pipe shouldn't be called iron pipe. But when people say "black iron pipe" they may mean steel pipe whether we like it or not.

At the same plumbing store, if you ask for "tin" you'll get galvanized sheet metal -- steel sheets with a coating of zinc -- no tin anywhere. If you ask for tin foil, you'll get aluminum foil. The practical answer is that you must rely on real specifications to describe what you want, rather than slang which will mean different things in different contexts.

Regards,

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
January 30, 2012

A. Actually black iron, by means of sheet, is Iron that is treated to withstand high heat. I'm not sure what type of iron it is or how it's prepared exactly, but I do know it's iron and not steel. I know this because a lot of our scrap cannot be tossed in the steel/galvanized scrap bins because the recycler will not take ferrous materials. Instead we have to take it to an all purpose recycler since we can throw the crap away in our dumpster. I work in a sheet metal shop, we use it primarily to fabricate heat exchange/exhaust ducts for AC/kitchens where stainless steel ductwork is impractical. Don't call a steel mill looking for it, call an Iron works or a metal dealer geared toward sheet metal for construction if you're looking to find this.

A. Hi Dyebhe.

With no disrespect, I don't think that's the question to ask or how to proceed. Rather, pick a standards body that you want to use, like ASTM or ISO, look up some standards for the kind of pipe you want, and check if they properly cover what you want (for example, pressure pipe vs. drain pipe, threadable vs. weldable). Maybe start with ASTM A53 [affil. link]. You will sometimes see an ISO or ASTM stamp right on the pipe. Good luck.

Regards,

A. Hi Lahiru.

The way I see it, you are taking a very imprecise piece of slang, "black iron", which means many different things to different people, and trying to put a fine point on it. I don't think it's possible to answer you. Sorry, but I think it's rather like asking us to tell you how many pounds a "heavy" rock weighs? Good luck; maybe I'm wrong.

Regards,

A. Black iron pipe, even though thought of as steel, is called as such because steel is an alloy mix of iron & carbon. Technically, the pipes are iron because steel is simply iron w/ hardening agents (alloys) carbon being the primary alloy hardening agent. All steel is iron. Because there are several classifications of pipe (stainless, galvanized, carbon/fiber, etc.) the traditional black iron classification was maintained for simplifying purposes, as the pipe truly is black iron.

A. Know cast iron from steel, just always heard carbon steel referred to as black iron. Cut and thread "black iron" for gas lines

Indeed S.; indeed Jeremy. Some readers want "black iron" to have a precise, well-defined meaning that precludes other people from using the term to describe other things, but life just doesn't work that way ...

To an infantryman, a "tank" is an armoured fighting vehicle, whereas to a fuel delivery driver a "tank" is a vessel to hold petroleum products -- and no matter how one group rants and shouts, that's the way it is. So too with "black iron".

Regards,

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
May 2014

A. Hi. "Black steel" is slang, not a specification. Still, Jason W claims above that if you call an iron works or a metal dealer geared towards sheet metal, rather than a steel mill, you'll all be on the same page. Good luck.

Regards,

A. To me, the term, "black iron" has a very specific meaning. It refers to generic ferrous metal of any specification which has NOT been plated or galvanized.

The term usually is not applied to things such as cast iron, tool steel of whatever specification that have their own generic labels.

In other words, black iron is iron or steel that can be welded without stray metals coating it that will poison the weld (or maybe the welder...).

Q. My question is, how do you achieve a black oxide coating on mild steel machined pieces?

A. Hi Jerry. Thanks. We have a "Black Oxide and Cold Blackening FAQs" you can start with; then if you use the search engine you'll find a dozen or more threads on the subject.

Regards,

A. Morgan, I don't think you will find any "uncoated" pipe. (nor would you want to because it would be pretty rusty) Regular black pipe has a sprayed lacquer type coating applied at the Mill where it's made to prevent rusting in transit and storage. Normally you can simply wash it off with an acetone [on eBay or Amazon] soaked rag. (making sure you keep changing rags and use plenty of acetone [on eBay or Amazon].) We have powder coated pipe which has not been cleaned as above, but the results are disappointing. You can use lacquer thinner [on eBay or Amazon] as well but I would avoid it. It's not healthy. Acetone is actually produced in the human body as a by-product of certain bodily functions. (As well as Chemical Plants!) Good Luck
Chuck

A. Hi cousin James. Something that you will discover without even leaving this page is that phrases like "black iron steel" or "black iron" mean different things to different people. That's because they are not specifications, but mere slang that people toss around. To someone who works in a steel warehouse offering steel and stainless sheets, 'black iron steel' or 'black iron' is going to simply mean 'the stuff that isn't stainless steel'. To a plumber who uses plain steel pipe and galvanized pipe, 'black iron pipe' is going to mean steel pipe. But to a specialized welder/pipefitter steel pipe may be a very different thing than black iron pipe ... and so it goes. You can't ask a third party what someone else meant with their slang.

High carbon steel is less ductile and more brittle than low carbon steel. So is black iron, if they really mean 'iron' ... but as I say, they may actually just mean 'plain low carbon steel' :-)

Regards,

A. Hi Helen. This page is replete with many different meanings for "black iron". So, unfortunately, you can't just call something black iron and ask questions about its suitability for applications. You probably mean the tank will be fabricated from hot rolled mild steel plates. This is not corrosion resistant, and it will rust; however, it will probably prove satisfactory for this application if the tank is closed so oxygen in the water dissipates. This is the most common material for the sprinkler piping.

But you should check with any regulatory agencies as there may be local codes you must comply with, and they may allow a less expensive plastic tank. NFPA may not apply in the Philippines (I don't know), but it is a well-developed standard for fire protection equipment, Good luck.

Regards,