Anodizing Aluminum Railing

[STrctPono]

I have some very simple aluminum railings that we designed that are being used for a pier in the ocean. The fabricator is substituting round tube for the flat bar that I had specified on the horizontal members. I don't actually have a problem with this other than the fact that they are calling out the ends of the tubes to be capped with a nylon cap. I don't like that. I wanted it seam welded on the ends. The entire assembly is being anodized. If proper sized and spaced vent holes are not installed, will this warp the member when they anodize it?

 

[TugboatEng]

Anodizing is done at low temperature so warping and internal pressure shouldn't be a problem. Holes are for drainage. Welding an enclosed space shut can be difficult. Shipyards and such won't weld on any size pipe unless it has been ventilated so they typically thread the holes for plugs.

 

[STrctPono]

Thanks Tugboat. I'm trying to understand the issues with welding a cap on the end. It's 1/2" dia. tube (pipe). What constitutes the required ventilation? I do care about the fabricator's limitations but in the end I am more concerned with long term durability. This is a pier open to the public and nylon caps seem cheap and unfinished. A few decades in the future and they fall out, stolen, or broken. The owner will not maintain this structure.

 

[TugboatEng]

I agree that the nylon caps are going to cause problems down the road. There will likely be corrosion between the plastic and aluminum and this will cause the anodized coating to fracture and blister.

The correct solution here would be to use solid bar since you're only talking half inch diameter.

Solid bar might also let you add some nice features such as mitered ends.

 

[3DDave]

The problem is that welding generates/requires a large amount of heat, an amount that causes the air in the tube to expand and blow the liquified metal back out of the weld. Even if it doesn't splash onto the welder it leaves a hole.

At that diameter tubing will either be weak due to a thin wall, or just as expensive as solid rod. Maybe the guy got a deal of discarded material and thinks this is a great place to over-price it? Dunno.

Not to your plan? Should not be your problem - contact a lawyer 'cause that's where this is leaning.

 

[STrctPono]

Ok. Thanks for the help. I need to have a discussion with them about seam welding a cap on and if they cannot then they need to go with what we specified (flat bar) or solid round.

 

[TugboatEng]

Solid round in that diameter is probably less expensive than tubing, especially when fabrication costs get involved. I would expect the welder wants a wall thickness to equal the part it's being welded to. Welding thin walls to thick material is quite challenging, especially for aluminum.

Just in case:

https://www.cfcanodizing.com/railing-and-welding-guidelines/

 

[MacGyverS2000]

A few decades in the future and they fall out, stolen, or broken.

A few decades? I would expect a few years maximum before they starting disappearing for various reasons... I wouldn't want cheap plastic plugs on an otherwise all-metal system, either.

Dan - Owner

http://www.Hi-TecDesigns.com

 

[MintJulep]

I think you should make the bars vertical rather than horizontal.

Otherwise they will all be bent by people climbing and jumping on them long before the caps fall out or corrosion becomes a problem.

 

[EdStainless]

1/2" Al is pretty flimsy, are you sure that you don't want something more robust?
Vent holes for welding are needed. look on an old steel bike frame. There will be a couple of <1/8" holes in the seat stays to provide venting during brazing.
Either way plastic caps are a bad idea.

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P.E. Metallurgy, consulting work welcomed

 

[IRstuff]

pier in the ocean

I assume that people will be climbing on the rails, permitted, or not.

I would agree with the idea to have the rails vertical, since that eliminates the climbing hazard, AND has the added benefit of not providing horizontal surfaces for seagull poop.

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[STrctPono]

Thanks all for your inputs. So we agree that the nylon caps need to go. I will discuss with the fabricator about the necessity for the vent holes.

As far as the comments related to the orientation of the railing (horizontal vs vertical). I do agree. Any job I have ever designed does utilize vertical balusters. This particular project uses horizontal since it matches the looks of the surrounding piers. A fall over the railing would put you 5ft below into the water. There is an open pier just below this so you could fall into the water there without any railing protection. In other words, the railing isn't really doing much for fall protection anyway.

 

[IRstuff]

This looks to be a decorative railing, which means ALL the people that would be using a working pier wouldn't be silly enough to even need a railing, but touristas are another story altogether, particularly those with young children, who love climbing

TTFN (ta ta for now)
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[TugboatEng]

STrct, you have missed the most important piece of advice here. At 1/2 diameter you should be using bar, not tube. All of your problems related to vent holes and end caps will no longer be present and costs will likely be lower as well.

 

[STrctPono]

Tugboat. I did hear you. It's not just a railing, however. The other part of the problem is that there is an entire aluminum gangway as well that is part of this project that was a delegated design. We provided specifications and general parameters but did not restrict them in terms of member shapes and sizes. They have an Engineer designing this and stamping it. I will certainly make comments on the first submittal review to use solid round or flat bar stock for these members. They may comply and then all will be well. If they want to play hard ball, it's going to be tough to contractually force them to. The second option will be to have discussions about seam welding end caps onto the 1/2" round tube and how they can successfully accomplish this.