Disguising Galvanising Vent Holes

Hi guys, I'm in the middle of making a bridge which is to be galvanised.

The middle upright 'pillars' which support the cables (it is a suspension bridge - small one) are curved tubes which have butt-welded pipe end caps on the tops.

This is to be galvanised and I need to put vent holes in the 'domes' on the ends. Afterwards I want it totally watertight.

What do people use to fill the holes - some kind of chemical metal stuff? If so which type shows up least on galvanised metal?

Cheers, Al.

Nothing. Fillers normally ends up looking worse than an open hole....imo.
Sometimes its possible to vent intertnally with minimal holes visible....
Have you already done it? can you put some pics of it up?


Why do you want it totaly watertight...? you can introduce other issues by making something completly watertight.

Filler and galv spray if you really need them hidden.
If it's just the dome head you need watertight, then some expanding foam filler should do the trick

Get some dome topped stainless tapered plugs made then knock them in, incorporate a small shoulder just below the dome to limit travel and keep the plugs even,

Pretty impossible to hide, i think if they are well placed, and equally spaced, as well as being as small a diameter as possible, they don't look too bad. You could try pushing a grey rubber plug into the holes?

Can't you get them to dip it upside down?

Luke said:

Can't you get them to dip it upside down?

Click to expand...

Still needs to be drilled

Its a drain, as well as a vent.... how about buying a big pack of silver BIC pens, and taking the endcap out

Welderpaul said:

Still needs to be drilled

Click to expand...

Oh.

I'm guessing then, that it's not as easy as dipping it upside down, and turning it over to drain off the excess over the tank?

You need the hole at the top, to allow the rapidly expanding gas to escape (due to heat)
And you need to have a hole at the bottom for excess zinc to drain.

Not something you'd want to be turning over really.

If your interested Luke, heres a little read....

Hitch said:

If your interested Luke, heres a little read....

Click to expand...

Ta, having a read.

I never put visible drain holes in much more than 8mm dia even on big stuff.

Thanks guys. Hmm, still not sure then.

The uprights are gently curved (nearly 25 metre radius) 88.9mm x 5mm wall mild tube and the end caps are 304 stainless. Would you believe no-one at the galvanisers (which is big and has been there for decades), nor at the 'galvanising institute' could tell me what would happen if I dipped 304 welded to mild tube, and if there would be a difference in the finish appearance. Amazing, I can't have been the first to do this??? anyway, i ran a mini test with some 2" tube and a 304 pipe cap to suit. Came out great - no difference at all. Did get a few laughs though - dipping an 8" length of pipe with a domed end with a hole drilled in it...

Luke - they can't really juggle it about - it goes down into the tank, and then goes up again, and thats it. To avoid getting a tube-full of zinc, I need a hole at the bottom too. Not only that, but if you imagine pushing a glass, the right way up, down into a sink of water it kind of wants to 'pop' out to one side as its less dense - same with this, so you need it to fill as it dips, ideally.

Its not actually watertight, its just the top domed end that is - purely to delay corrosion, the bottom still has drain holes just in case.

W/Paul - the guys down there told me they wanted 12 to 14mm holes, so I guess I'll do 10mm.

Still looking like chemical metal with some zinc spray after...

Cheers, Al.

Al, couldn't you do the domes separately and fix them in place later? Perhaps a smaller bit of tube on the bottoms to provide an interference fit or something to put some stainless screws into. I'd do anything to avoid chemical metal!

Why the stainless endcaps if you are galving?

As for filling holes, i doubt it will make an ounce of difference to delaying corrosion, the inside will be galvanised aswell as the outside anyway.

Hole sizes, something that size, 10mm minimum really. HAve they got base plates? Or do you need to drill hanging holes also?

Beware, if they think it hasn't got enough holes, they will charge you to blow some in with the gas torch.

Thanks guys, yeah I discusserered it all with them. They told me where to put the holes and how they'd wire it up for the tank etc.

They have base plates with holes, so that end is easy.

This is really a cosmetic issue. I don't want the end full of holes as its not that far above eye line, so pretty obvious. I know the galv will be sufficient. This bridge has a 10 metre span over a small river, so its only a freshwater evironment.

I went for stainless caps as they were about 3 quid each, and the best price I found for mild was literally about 15 times that. Anyway, I liked the idea of the extra corrosion resistance.

Here is my test piece that caused all the raised eyebrows. Some joker wrote 'sure to make you smile' on the ticket...

there is no way (that I know of) to stop the weld showing up - even if you give it to them ground perfectly smooth, it attracts more zinc than the rest of the metal (due to the silicon in the wire is it?).


Cheers, Al.

Hmm, I'd be inclined to cap off the tubes and leave it with the drilled vent/drain hole in. Seems a lot of trouble having ss caps etc. You must have a good price in.

cant you tap the hole and whack a threaded insert into it?

Can anyone actually state why they don't like chemical metal? I've never used it, but this is just a cosmetic filler - what exactly is the prob with it? Cheers, Al.

I've used plastic padding and JB weld for various repairs and not had problems with either. I can't see why they shouldn't be used cosmetically and JB weld is definitely water resistant. Tapping the hole would cut through the protective coating exposing bare metal defeating the object of having it done.