Thread: rust affected scaffold pipe

provided the rust is only on the outside -- i.e. no internal rust -- years and years ago when what I knew about structural engineering was still fresh in the mind, I would probably have accepted the pipe by reducing the effective OD and wall thickness to account for the metal lost to rusting. eg. if the deepest rust pitting is 1 mm then the effective diameter would decrease to around 46mm and the wall thickness to 3 mm.

Structural testing of your pipe would possibly cost more that buying new material.

If you're intending to use the pipe for truss chords, as an engineer I'd be more concerned with issues related to
1. how straight the pipe is
2. damage to the pipe such as kinks, dings, etc -- which could result in localised weaknesses
3. how good your welding is -- assuming you're using welded connections
4. steel strength

not necessarily in that order

if you need to obtain a structural certificate for your trusses, your best option may be to build them with what you have to hand and then get a "compliance" certificate based on test loading each truss. Again from my ancient memory, if the deflection under the design load (or some multiple of that load -- like 1.5 or 2 times) is less than a certain amount, a component can be certified as "complying"


Engineers are trained to design things so they just stand up under the design load.

in your case overbuilding may be the best option.


please don't rely on the above, if your trusses will need any form of certification, pay for some professional advice

How do you intend to treat the rust on the pipe? I would be concerned that the amount of effort and time taken to produce a surface suitable for painting would exceed the cost benefit of using the pipe you already have. From what I can see, there will be much scaling and wire brushing before your pipes are anywhere near usable.
Perhaps your scaffold pipes are best utilised for another project although I fully realise that this will require the purchase of new materials for your trusses.

I agree with Karl this is not going to be worth the hassle. Extensive X-RAY testing would be needed to demonstrate that the pipe would be worth doing BEFORE rust treatment, and because rust treatment can affect the strength of the steel, testing AFTER the rust treatment as well, so you would in fact have to pay for twice as much testing as you think. I can just see the metallurgical labs shaking their heads over certifying this one.

I'm not sure what you are chasing here, is it the texture of the surface that you would like to retain. If so it may be easier to make a truss and the clad the real truss with the rust treated items by slipping them over full strength chords ?

Personally I would be looking for a completely different solution using hi-build textured finishes but you may need to do a lot of experimentation to find one that looks like rust.

Hi Bob

I suspect Meadow is trying to save $$ by using material he has on hand.

Trying to apply limit state design using the material would be a very expensive process, as you point out.

However, if the tubes were part of an existing load bearing truss and as rusted as some of them are, test loading would be used to determine a safe working load. The technique is frequently used to assess the condition of old bridges.

Thanks Fellas,

All good points you make,

At 3$ a stick purchase price I can afford to play around with the science to rate this material I think??

The thought was to sandblast and then dip in liquid rust converter/treatment fluid, perhaps in a gutter type bath, then prime paint etc

Fair bit of handling I know for 100 sticks.

Interior of pipe is good and pitting has shallow profile.

I'll keep you posted : )

Originally Posted by meadow street

Thanks Fellas,

All good points you make,

At 3$ a stick purchase price I can afford to play around with the science to rate this material I think??

The thought was to sandblast and then dip in liquid rust converter/treatment fluid, perhaps in a gutter type bath, then prime paint etc

Fair bit of handling I know for 100 sticks.

Interior of pipe is good and pitting has shallow profile.

I'll keep you posted : )

Ummmm.

How big an air compressor do you have?

How big a sandblast pot?

How much experience do you have in sand blasting?

Have you factored in how much garnet you're going to go through? It's illegal to use silica sand.

Where are you going to do the blasting?

How many hours do you think it's going to take you to do it?

Better have answers to all those questions before you go down this path. I know a little about blasting and IMO you are in for a world of pain......

FWIW there's no way I'd use pipe like that for any load bearing structure and I'd run a mile from anything built with it. If you're way out in the bush somewhere, maybe it's OK, but I, personally, would not do it.

PDW

Originally Posted by PDW

Ummmm.

If you're way out in the bush somewhere, maybe it's OK, but I, personally, would not do it.

PDW

Wow, that's pretty crappy pipe.

+1 on what he said.

Sounds like a lot of work and electricity.

Rob

There are different cans of worms that the use of the corroded scaffold tubes open up.
My feeling is
*That the engineers contacted may not be all that interested.
*That a Nata certified lab and engineers report will be far more costly than you anticipate.

Having worked for a Nata certified lab , I can say you will not be offered an opinion.

You will receive a professional report which will basically state that the item/s being examined complies with or does not comply with the overarching Australian Standard that principally applies to the job/work/project you are undertaking.

It is the engineer who does the report based ( if necessary) on what the Materials testing lab report provided.

X-ray inspection(no its radiographic, go to the hospital for an XRay) is too costly given the application of the items.To buy,operate maintain and store an isotope,there a numerous standards and regulations to comply with for using radiography as an examination medium.It is these cost of complying that makes radiographic examination costly, as it based upon more than time taken to shoot, develop and interpret film.

The loads that the truss could be expected to bear needs to be accurately calculated and given the sporadic disposition of corrosion a examination type for defects it is likely to be magnetic particle and /or Ultra sonic exam- Checking out each and every tube is likely to be a royal PITA. It is a fitness for purpose thing and to determine each component is fit for its purpose is likely to get expensive.

The other thing of course is the amount of risk that failure of the truss exposes you to. If its a chook shed almost none or is it a structure where public risk cold be involved?

I don't want to sound negative but its better to have full information before committing to anything.

Grahame

Originally Posted by Grahame Collins

There are different cans of worms that the use of the corroded scaffold tubes open up.
My feeling is
*That the engineers contacted may not be all that interested.

Some of my friends are professional engineers, got the liability insurance and all.

There is NO WAY they'd have their name or stamp on anything built out of pipe like that.

Sometimes 'cheap' turns out to be very, very expensive. It's not like *new* 32NB Sched 40 pipe is all that expensive......

PDW

Last time work hired a structural engineer I think the rate was something like $350 per hour. Say a report takes 2 hours plus another 2 to 4 inspecting the tubes (as the corrosion would not be able to be generalised) and I think even if you did find an engineer game to put their name to a report you would be several thousand out of pocket.
How much per metre is replacement tube?

Michael

Yes I'm starting to hear properly now

: )

What span will your trusses be?
If I were building trusses, I would go for Duragal SHS by choice due to it's ease of fabrication and corrosion resistance, requiring only the welds to be touched up.
You will probably find that your completed truss may be up to 30% lighter in to the bargain.
Overall, I think that the cheap scaffold tube may cost you more than it saves long term.
Have a look at this for some ideas. http://www.bjhowes.com.au/HopleysOpe...t-Brochure.pdf
The HJ350 and 450's use 50X50X1.6 SHS Chords and 20X20X1.6 SHS webbing (actually it may be 25X25, my memory is arguing about that one, been a few years since I eyeballed one of these). The smaller trusses can be replicated using 50X25X1.6 RHS Chords and 20X20X1.6 webbing. The SHS and RHS Chords are much easier to affix purlin cleats to than pipes as an added bonus.

Nice one Karl, I did spy some hopleys recently and wondered about them as a real alternative !

I think the scaff can go to the local auction for the farmers to play around with.

Hopefully make some $ on them too.

Back to the drawing board : )