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topic 3428

Bending anodized aluminum pipe


Q. I want to know if I can anodize aluminium pipe before bending without cracking the plated area. The pipe is 7/8" o.d , 0.065 " wall thickness. material:aluminum 6063-T5 Bending 90 deg.bending radius 2.5 X D. Thanks

arie p [last name deleted for privacy by Editor]


A. Anodized coatings are very hard and brittle. According to "Properties of Electrodeposited Metals and Alloys" [link is to info about book at Amazon] by Safranek, this is something that, to paraphrase Miss Manners, "simply isn't done".

Ted Mooney, Teds signature
Ted Mooney, P.E.
Pine Beach, New Jersey


A. Hi Friend,

I have read of a Florida company that daily builds custom boat towers for large yachts from anodized aluminum pipe & tube materials and daily bends and even WELDS anodized materials including for newly ordered custom yachts, like Hatteras and Viking Yachts which were mentioned in the article. Based on that article, it seems not a problem to bend anodized alum. The article I read was mostly about TIG welding techniques they use to weld anodized aluminum. I don't recall the company's name. Bending anodized alum. seems not a problem.

John M [last name deleted for privacy by Editor]
- Alamo, California


Q. John M,

I am a beginning fabricator of the boat towers that you mentioned and would like to read the same article you read. could you give me more information as to where you read it , as I think it may be quite helpful to me.

Thank You!

Joe L [last name deleted for privacy by Editor]
- Weslaco, Texas


A. I have the article (in a .pdf file) on the boat company that welds anodized aluminum in the tower manufacturing business.

Bill C [last name deleted for privacy by Editor]
- Dunnellon, Florida USA


! ! Our company is an anodizer of aluminum and I would disagree with the assertion that bending anodized tubing is not a problem. I would imagine that the boat towers that are being built are anodized after they are bent rather than the other way around.
The anodize coating has a hardness that approaches that of diamonds. This coating for most marine applications is 0.0004" thick. Bending of the substrate is no problem as it is so soft but, the coating that encase it is so hard it is like trying to bend an M&M. The shell will crack.

Michael Hancock
- Indianapolis, Indiana USA


Thanks, Michael. I agree with you and, although the referenced article discusses welding anodized aluminum, I didn't see a claim that they bend it after anodizing as John M asserts.

Ted Mooney,
Teds signature
Ted Mooney, P.E.
Pine Beach, New Jersey

January 1, 2009

! ! I build boat towers, ladder racks, etc. everyday of my life and other products made of anodized aluminum. Yes you most certainly can bend this stuff after it is anodized. You need the proper tooling and experience to work with anodized material. Its not for everyone and separates the entry level fabricator from the professional in my opinion.

Larry Trainor
Far Beyond Fabricating - Bayville New Jersey

January 3, 2009

Thanks, Larry. Anodized coatings are ceramic and cannot be stretched at all. As Michael says, they are like an M&M or an eggshell.

As with anything else, experience counts, and I'll trust that you are able to bend the tubing such that you get hundreds of tiny cracks instead of a few dozen large ones, and are able to avoid the ugly white discoloration that less skilled fabricators get, and which is illustrated and which you commented on in letter 25645.

I would be very curious to see an ASTM B117 [link by ed. to spec at TechStreet] salt spray test on these post-anodizing fabrications to learn how they fare in certified corrosion testing. Maybe the cracks are small enough that the corrosion of the exposed aluminum is not an issue. I know that anodizing also cracks from expansion of the aluminum when it is strongly heated, yet hard anodized frying pans seem to held up fine. Thanks again.


Ted Mooney,
Teds signature
Ted Mooney, P.E.
Pine Beach, New Jersey

January 3, 2009

Feel free to stop by my shop and pick up a free sample. I will bend a piece for you and you can test it. I have seen My towers abused by salt water after 10 years look good. anodizing is an electrical process not a ceramic coating.

Anodizing: Aluminum is immersed in a tank containing an electrolyte having a 15% sulfuric acid concentration. Electric current is passed through the electrolyte and the aluminum is made the anode in this electrolytic cell; the tank is the cathode. Voltage applied across the anode and cathode causes negatively charged anions to migrate to the anode where the oxygen in the anions combines with the aluminum to form aluminum oxide (Al2O3).

Larry Trainor
Far Beyond Fabricating - Bayville New Jersey USA

January 7, 2009

Thanks, Larry. I spent my whole career designing, installing, and starting up hundreds of anodizing and plating lines, so I understand how anodizing is done. I probably should have used the term 'ceramic-like' rather than 'ceramic' in making the point that anodized coatings have no elasticity.

My curiosity is not sufficient to authorize the cost of a salt spray test when I have no way of recovering the cost, but hopefully some reader may come along who wants to take you up on this. Thanks again!


Ted Mooney,
Teds signature
Ted Mooney, P.E.
Pine Beach, New Jersey

February 6, 2009

Q. Could someone tell me if anodized alum tube is coated on the inside as well?

Peter Cowan
- Lakefield, Ontario, Canada

February 18, 2009

A. Hi, Peter. It can be but it's much more common that it's not. Please tell us your situation: marine tubing, condominium guardrail, machine component, chemical piping, etc. Thanks.


Ted Mooney,
Teds signature
Ted Mooney, P.E.
Pine Beach, New Jersey

July 16, 2009

Q. Hi, before I spend thousands of dollars on aluminium pipes I wonder if I could ask you if 3/4" or 1" aluminium pipe (schedule 40?, series 3000-5000 alloy, T-0 annealed) can be easily, or at all, spirally wound around a 7" pipe (as a form). The aluminium pipes are 25 feet long and need to wind about 3 times around the length of the form.
Asking as a sculptor spending someone else's money.

Dodo Na
Sculptor - Galway, Eire

August 14, 2009

A. Hi, Dodo. Well, I'd suggest buying one or two pipes and trying it, rather than buying thousands of dollars worth :-)

... but I think a 3/4" pipe wrapped around a 7" mandrel would be doable (remember that 3/4" pipe is a little over an inch in O.D.). I think a thinner wall tubing or a lighter schedule pipe would be easier to bend. Good luck.


Ted Mooney,
Teds signature
Ted Mooney, P.E.
Pine Beach, New Jersey

May 5, 2011


Steve Branden
STAINLESS - Mission Viejo, California

January 31, 2012

A. Hi Dodo, try filling dry fine sand in the pipe and bend, it will bend without any cracks. Even if it is of small wall thickness.


October 10, 2014

A. Yes it can be bent, I watched a tower builder buy all anodized tubing and components then bend weld and build the towers. I bought the materials and built my own. You can bend it but you need a special bender that supports the sides of the tubing, a regular steel tubing bender will make it kink. Then you can heliarc weld everything and paint the welds over with silver paint.

Paul johnson
- Boston Massachusetts

October 5, 2016

Q. What type of corrosion are you afraid of? Isn't the surface film created by anodizing the same as what aluminium itself creates when corroding only the anodizing process makes it thicker and even?

Hallvard Tyldum
Stokke AS - Alesund, Norway

October 2016

A. Hi Hallvard. Yes, anodizing does create a controlled oxidized film on the aluminum, but that does mean that the "corrosion product" created by anodizing is exactly the same as from natural corrosion. Anodized coatings are thick, uniform, and considered attractive, as a result of the fairly high voltage/current that is applied, followed by controlled sealing, whereas more random corrosion can be rough and quite ugly.


pic of Ted Mooney
Ted Mooney, P.E. RET
Pine Beach, New Jersey
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