Different metal types and corrosion

jack action

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I need to bounce some ideas off you for my project.

My project is to build an exterior handrail, using these flanges:

4936t72p2-i02fl_635507143640000000.png

The actual inner diameter (ID) is 1.66" and the material is galvanized steel.

I was supposed to use the appropriate pipe size for the handrail made also of galvanized steel, but machining constraints left me with 1.5" OD HRPO steel (not sure of the grade).

My plan is to apply a zinc-rich primer (92-95% zinc) to the steel handrail and a coat of paint to increase the corrosion resistance.

To compensate for the diameter difference, I want to use a piece of tubing with the following dimensions between the flange and the handrail: OD1.625" X ID1.509". I have a choice between aluminum 6061-T6 and steel 4130.

I'm not sure yet if I will have to link the tubing to the handrail with some screws (since only set screws are holding the handrail to the flange).

Which material is better for the tubing?

Aluminum is easier to work with if I need to, but it also have a different thermal expansion rate than steel (usage is between -40°C - 40°C). Will this affect the set screw setting to hold the hand rail? Does the aluminum against zinc (either galvanization or zinc-rich primer) causes problem? But I also think the aluminum tubing should deform easier than steel tubing and work better with the set screw design of the flange to squeeze everything and hold tight, or am I wrong?

With steel tubing, I intend to use zinc-rich primer as well. If so, should I also apply the paint before assembling the handrail-tubing-flange together or just leave everything on zinc and paint after everything is assembled? Using steel, is it playing with fire and having corrosion quickly setting in between the handrail and tubing?

I was also wondering about the length of the tubing. I was thinking of having the tubing a little shorter than the depth of the flange, and maybe seal the top of the tubing - between the handrail and the flange - with paintable latex to prevent water and snow to get in between each component. Is this a good idea?
 

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Bystander

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Canada? Maritimes? Salt/saline? You know the advice you get is going to be worth exactly what you're paying for it?
With the reminder to remind/inform people who aren't familiar/acquainted with you taken care of, I'd stay away from the aluminum; just too little quality control at your level of "consumption."
 

jack action

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Tom.G

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To consider:
  • You are mixing two or three dissimiliar metals in a wet environment, Iron, Zinc, maybe Aluminium. Guaranteed to corrode and disintegrate. Galvanized works pretty good by itself, until the Zinc layer is compromised. At that point, due to electrolysis, the Iron corrodes faster than bare Iron would. Adding Aluminium will just speed up the corrosion.
  • For a secure attachment to the flange, a threaded joint is best. Get a flange to match the pipe size and have a plumber thread the pipe as needed. With the variable side forces and long lever arm, you will be regularly tightening those set screws.
  • If you use the shim approach, what keeps the pipe retained in the shim?
  • Remember that _any_ movement at a joint will crack any paint or weather proofing and let water in. Then you must address the water freezing in the confined area in/under the flange.
  • Use a full size pipe flange (circular, four mounting holes); again to handle the side forces and long lever arm.
  • Pay attention to both the material you are attaching to and the attaching method. Again that long lever arm

Cheers
Tom
 

jack action

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You are mixing two or three dissimiliar metals in a wet environment, Iron, Zinc, maybe Aluminium. Guaranteed to corrode and disintegrate. Galvanized works pretty good by itself, until the Zinc layer is compromised. At that point, due to electrolysis, the Iron corrodes faster than bare Iron would. Adding Aluminium will just speed up the corrosion.
That is what I was afraid of. I knew some metals can't be mixed up in corrosive environment, I just didn't remember which ones. I 'll stick to steel for simplicity.
For a secure attachment to the flange, a threaded joint is best. Get a flange to match the pipe size and have a plumber thread the pipe as needed. With the variable side forces and long lever arm, you will be regularly tightening those set screws.
[begin rant]

That was my first idea, but you wouldn't believe the difficulty I had finding someone doing simple machining for this project at a good price (plumbers included). I couldn't even find a machine to rent - at a reasonable cost - to do it myself either. I reduced my «subcontracting» required work to do only 3 bends in a pipe and I ended up finding a guy doing it for 80$ (material included), but he didn't have the exact die size I needed, hence the compromise. I had 2 or 3 other «pros» who could do it with the proper pipe size, but it would have cost me at least 3 times more. Given the original material (galvanized pipe) details at 55 $ and it took the guy 1 hour to do the job (which is what I expected), I have a problem with giving that much money to strangers for so little work.

That being said, the flange is designed for handrails - even bigger than the one for more project - and many suppliers used that system (with set screws), so I took a leap of faith.

Since I have a big problem finding good help to do the job correctly, I tried to keep a lot up to me to make proper adjustments. It is a simple design, but there is a lot of geometry and people really don't understand the concept of tolerance accumulation, even if I specified it on drawings and put emphasis on it while talking with the guys. You have no clue how close I was to buy my own bender and do it myself.

[end rant o0)]
If you use the shim approach, what keeps the pipe retained in the shim?
That is why I want to put a few screws through the shim and handrail to keep them together, instead of relying on friction alone. If someone pull the handrail up, if something moves, the shim will have to come up with it.
Remember that _any_ movement at a joint will crack any paint or weather proofing and let water in. Then you must address the water freezing in the confined area in/under the flange.
Yes, weatherproofing as an assembly is not a good idea. I will do my best to treat each component individually.
  • Use a full size pipe flange (circular, four mounting holes); again to handle the side forces and long lever arm.
  • Pay attention to both the material you are attaching to and the attaching method. Again that long lever arm
All of this was addressed and acceptable compromises were done to accommodate all the particularities of this project.
 

ChemAir

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Is this a real handrail for safety, that might require local engineering design and permit, or is this purely aesthetic/non structural?
 

jack action

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Is this a real handrail for safety, that might require local engineering design and permit, or is this purely aesthetic/non structural?
It is a handrail for a small 5-step (##\approx## 3 ft high) exterior stairway at my home. Mostly to help keep balance when people use the stairway (There was none for the last 70 years). No permits involved. Here is the old stairway:

stairway.png

The new one (still made out of concrete) has an extra step and a wall on each side to keep the soil from tumbling down. The ramp will be bolted on one of the wall and it will look like this:

stairway-new.png
 

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Why use a bracket at all?

A little pre-planning and you could have cast some sleeves into your new slab. Suitable recesses could still be drilled.

Your design looks simple enough to bend up. Deicing salt is going to play havoc with any carbon steel. Expect a yearly maintenance chore if you don't use some sort of stainless. Match the stock to the strength, drill holes to spec for a tight fit to the stock, bend, set, caulk. Removable for inspection and no paint needed. Trade off: higher material cost.

Return: some kid balancing on your handrail which exists at the streetside, readily accessable to the public for foolish stunts, will not someday be surprised that the coat of paint over your structural rust at grade is inadequate to support his weight, leading to a potentially nasty meeting of said fool's head and unyielding pavement.

Any range of slip-fit designs, embedded pegs, ect, would seem preferable to the IMO anemic brackets being considered for something installed ostensibly for safety. Might not hurt to check with any possible legal ramifications of placing safety railings ect potentially in public right-of-way.
 

jack action

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@krater ,

Thank for reviving the thread. I'm in the process of installing the handrail and was planning for an update afterward.
A little pre-planning and you could have cast some sleeves into your new slab. Suitable recesses could still be drilled.
First, I'm usually not a big fan of things that cannot be dismantled (especially custom, one-of-kind, untested designs), but «pre-planning» is very difficult when the people designing the concept, building the stairway, building the handrail and installing the handrail are 3 different persons who don't know each other. When the builders like to «play it by feel» despite plans, it makes everything even more complicated. As the one designing, I «pre-planned» the possible deviations from the original plan and figured out easy ways to make the appropriate adjustments when connecting everything together.

I finally found the perfect shim. It is an exhaust pipe connector. It is designed to slide on a 1½" OD tube and its OD is very close to 1¼" pipe. The material is aluminized steel, so I have some corrosion resistance. Best of all, the length is 4" so I don't have to cut it, thus not exposing the steel core of the pipe. With a 4" length, the shim protrude about an inch from the top of the flange, giving a more pleasing transitional look than having a «small» tube going directly in a «large» flange.

I decided that I will put my zinc-rich primer on the handrail, put some paintable latex in between the handrail and shim to both prevent water going in and create a bond stronger than friction alone between them. I will then paint the handrail and flanges (in & out) separately and assemble them afterward.
some kid balancing on your handrail which exists at the streetside, readily accessable to the public for foolish stunts, will not someday be surprised that the coat of paint over your structural rust at grade is inadequate to support his weight, leading to a potentially nasty meeting of said fool's head and unyielding pavement.

Any range of slip-fit designs, embedded pegs, ect, would seem preferable to the IMO anemic brackets being considered for something installed ostensibly for safety. Might not hurt to check with any possible legal ramifications of placing safety railings ect potentially in public right-of-way.
The assembly will be a lot stronger than one might think:
  1. The flanges are not parallel;
  2. Fitting the handrail to the stairway demanded that I inserted a piece a wood to push the handrail ends away from each other to create the proper alignment. When I will remove this piece of wood (I had to used tie-downs to insert it; very tight), there will be a large spring force acting on the flanges, i.e. a lot of friction;
  3. Distorting the handrail to correct these misalignments ended up with the top end of the handrail being about 15° from vertical as it was intended. The play between the flange & the tube still allows this misalignment without creating a «crooked» look to the unaware eye.
For these reasons, I don't think it will be possible to simply pull on the handrail to remove it. Even if the setscrews weren't tighten. I really don't think the term anemic will apply to this assembly.

Thanks to all for humoring me in my train of thoughts, it was helpful.
 

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