Drill Hole in Stainless Steel Pipe

[feudalkaos]

Originally Posted by Cadence

Question, why do the uprights appear to run wild?
I might be tempted to weld a diagonal from the upright to the horizontal, on both sides if for no other reason than symmetry, making it span as much as possible without interfering with your dinghy. From your diagram it appears that all of the stress is right at the weld right above the hole. Unless I'm missing something, I don't like that design with the right angle baring the load. It is probably fine for the panels, was the use as davits an after thought.

Attached is a more accurate picture. In the previous pictures I had forgotten about the supports between the vertical and horizontal bars for the davits. You can see in this picture that there are supports welded between the furthest back horizontal pipe and the uprights. These are 1".

The davit was the original purpose I assume.

[feudalkaos]

Originally Posted by garyfdl

The biggest problem people have drilling/cutting SS is they try to do it too fast. Stainless work hardens so you need to work it as slowly as possible.

Agreed. It was fairly easy to drill. I drilled very slowly with a oil and lots of breaks to cool the tool and work piece.

Stainless work hardens very easily with heat so drilling quickly is what causes it to become difficult to drill. Keeping the temperature low allows it to cut pretty easily.

[feudalkaos]

Originally Posted by Dave_S

No care, no responsibility

It seems to show similar stress in areas where and between where the pipes join as around your holes. The load is applied vertical down and horizontal.

I still suspect the frame will fail at the hole if over stressed but I think it is ok. This is with a total load of 6000N, this is a load you could reasonably expect in rough weather with no safety factor and no deformation.

P.S. I doubled the lateral loading with no deformation, I think it's fine.

Nice model! Thank you for checking this for me. So are you saying you modeled this with 12000N and it still didn't deform?

[feudalkaos]

Originally Posted by AKA-None

If you want to provide stress relief the easiest that doesn’t look like crap would be to insert a small collar into the hole and weld it.

I am considering doing this as a backup. I do not have access to welding right now so am thinking about epoxy welding something in as a temporary substitute.

[waterman46]

There appears to be zero cross bracing to counteract diagonal loads you would experience at sea. Perhaps there is some good bracing at the mounting points on deck, but it doesn't show in the diagram. And bracing at deck mounts would take up valuable deck space. I would have originally designed it with diagonal tubes welded at each of the upper corners. Don't need to be more than about 1' long. But of course, then you could not have drilled that hole! Add them now if you are worried.

[Cadence]

Originally Posted by feudalkaos

Attached is a more accurate picture. In the previous pictures I had forgotten about the supports between the vertical and horizontal bars for the davits. You can see in this picture that there are supports welded between the furthest back horizontal pipe and the uprights. These are 1".

The davit was the original purpose I assume.

That makes all the difference in the world. You are probably OK.
Enjoy yourself.

[Dave_S]

Originally Posted by feudalkaos

Nice model! Thank you for checking this for me. So are you saying you modeled this with 12000N and it still didn't deform?

Again, I take no responsibility for the information here.

Apologies, the total load was 9,000N and is shown in the image below.

The model has been tested as one part, it is not an assembly with welds so it considers the joins to be solid.

It is fixed or supported only at the base.

It is only testing the parts you can see.

The material tested is Austenitic Stainless Steel, the round hollow section is 2" OD 1.65mm wall thickness.

The ends of the arms have been edited so as not to fail at the load points.

The yellow arrows show the direction of loads applied to the part in its original location.

The vertical each have 1500N and the horizontal each have 3000N applied.

The displacement is set to actual.

The test showed negligible plastic deformation.

This is Autodesk Inventor a professional FEA program - I use it for testing mechanical parts and assemblies in electro-mechanical systems. I have not used it for round hollow section before.

It has proven to be remarkably accurate in my work, we test up to 30,000N on small parts and assemblies, in our destructive testing actuals are always pretty close to FEA results. However it depends on the accuracy of the part to give a good result and I don't have accurate information on your frame.

P.S. I agree it should have cross bracing to limit the deflection as it may work harden and fail.

[hpeer]

Dave,

Thanks for doing the simulation and sharing the results.

I am a little confused by the apparent asymmetry of the deformation. Is this because of the hole?

[Dave_S]

Originally Posted by hpeer

Dave,

Thanks for doing the simulation and sharing the results.

I am a little confused by the apparent asymmetry of the deformation. Is this because of the hole?

No, there is only some change from the holes, the port side upright has a torque applied to it centred around the starboard upright which is adding to it's direction of deflection, where the starboard upright has a torque applied which is to some extent countering the deflection.

The colours are the stress in the material when the load is applied. Almost all the deflection shown is elastic and will return when the load is removed. Don't forget this is at a higher load than you should see.

[hpeer]

Yes, of course!! Duh!

Thanks.

[waterman46]

Knowing what will happen with a 9000nt static load in a single direction is certainly a good start, but not the whole story by a long shot.

You really need to know or approximate the expected dynamic load in seas. Weight of dinghy, solar panels and the structure itself, put in motion on various trajectories due to acceleration at the mounting points caused by big waves knocking the boat and it's stern in all directions. To be accurate you would need measurements using accelerometer in big sea conditions. Or maybe a naval architect can calculate it.

Or just add the short braces recommended by several of us and be done with it. I'm surprised they weren't included in the original design.

[Bbolino]

If the hole was created for wiring any welding will burn it up. make sure you pull it out before welding
That frame has as much lateral load as downward load, maybe more.
Odds are that it is 2" for aesthetic reasons more than strength reasons but you don't know and the hole is very large for the pipe diameter. Its existence near a welded connection provides an additional and stress point
At a minimum it should be regularly inspected for any signs of cracking
There has to be a structural engineer on this list who can describe the proper way to reinforce it. I would suggest a full-size brace pipe saddled onto the pipe below the opening and onto the cross member above (on a 45 deg angle), probably with a matching one on the other side. that should restore the lateral strength and stability.
I would also make sure there is a drain hole at the base of the vertical. its going to accumulate water which will eventually affect the wiring and salt water will corrode stainless steel, especially if it isnt 316 stainless

[skenn_ie]

Definitely, a diagonal below the hole would be good, preferably right to the bottom of the upright. 1" pipe would be sufficient That applies even without the hole. Triangles work best. Currently a very poor design IMO.

[StoneCrab]

Originally Posted by sy_gilana

I would weld a short piece of pipe into that hole, about 3/4" long, and push fit half way in, then weld all round.

This idea is basically what an engineer would have you do...basically the idea is to replace the metal you removed by cutting the hole by either adding a stub or a collar around the hole.

If you look at any commercial tank or piping, you will see extra metal surrounding any hole, tee or pipe sticking out of the tank. It looks like a big washer that is curved to the shape of the pipe at the base of the joint.

One advantage of doing the reinforcement is that you then have a broader shoulder contacting any wires exiting the hole.

Roughly, if you calculate the SQ mm of metal removed by the hole you drilled (pi * radius squared x thickness), you can calculate the thickness and width of the reinforcement pad (or collar). This will effectively restore the strength to its original spec.

[StoneCrab]

Replacing the metal from the hole will restore the pipe's strength but if it was undersized for the application originally, it can't change that fact, or the result. Failure just won't be because you drilled the hole.