Drill Hole in Stainless Steel Pipe

[MJH]

Originally Posted by feudalkaos

I have a a 2" Stainless Steel upright pipe 16 gauge that holds up my davit system. I drilled a 1 1/8" hole in the pipe to allow wires to run down the pipe and into the boat.

My after thought concern is the possibility of weakening the pipe. I have attached an image to help illustrate.

The hole is under a cross member that would likely keep the pipe from being about to collapse in the direction of the hole but I hope to get some other opinions.

My goodness, how many wires do you have...a 1.125 inch hole!

When I install my stainless steel arch solar panels I elected to keep the wires exterior to the pipes and secure them with wire ties. It makes the install and tracking electrical issues/servicing them when necessary so much easier. Yes, the wire ties have to be replaced after a time but that is a small inconvenience compared to working inside tubes. As a matter of fact I just had an issue with one solar panel and the disconnect was easily identified...inside a pipe would have been a nightmare.

I confess this was based on my experience installing a new Edson stainless steel pedestal where I did run wires down inside the tubes to under the cockpit...what a PITA and the drilled entry holes into the pipes are prone to cut into the wires eventually.

~ ~ _/) ~ ~ MJH

[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.

[Dave_S]

Originally Posted by feudalkaos

I was mistaken, the cross member is 2in.

Attached are 2 more pictures showing how the dinghy sits.

I think there is potential for a problem it may never happen but the way it is the tender movement port to starboard provides a torque through the uprights and with the hole where it is and particularly as you say there is a matching hole on the other upright may provide a weakness for the pipe to deform by twisting at the hole level.

[Martkimwat]

Quite apart from the hole which has weakened the pipe, it seems a hell of a lot of weight supported by only a 2" butt weld on pipe in shear with one hell of a lever, I'm surprised the weld hasn't failed, irregardless of holes you now have under each weld which could now cause the pipes to buckle at the holes, since there is nothing much stopping it apart from the integrity of the pipe which is now compromised. I'm sure some one could calculate the static stresses knowing the weights and the lever arm of each support, then triple that figure to allow for dynamic loads. If it is still within the stress calculations for the pipe (which I would doubt), I would still be concerned about the holes. a piece of even 1" diameter, thick wall stainless tube about a foot long welded across the two pipes, bisecting the angle would create a massively greater support by spreading the shear stress over a much greater distance.(belt n' braces)

[captlloyd]

You have nothing to worry about.

[hpeer]

OK here ya go. An online calculator to figure out the real numbers.

https://amesweb.info/stress-concentr...round-bar.aspx

Please let us know how you make out.

Good luck!!!

Edit: OOOPSIES
The calculator will not work with hour parameters
The pipe is too thin
The hole too large with respect to the tube OD

I put in the max allowed numbers ad found that this hole increased the bending and torsion loads by almost 4 times. (If i read it correctly). Your situation will be significantly more.

[Rorzech]

[QUOTE=feudalkaos;3268416]I have a a 2" Stainless Steel upright pipe 16 gauge that holds up my davit system. I drilled a 1 1/8" hole in the pipe to allow wires to run down the pipe and into the boat.

Just how many wires is that hole supposed to handle ? Wouldn't a 3/4" hole with smooth edges suffice ? It would be exponentially stronger.

[billgewater]

I bet many readers would be interested in just how you managed to drill such a large diameter hole so cleanly through the SS tube wall!
There have been a number of threads on SS drilling problems!

[garyfdl]

I specialized in fluid power engineering so my structural is really rusty (no pun intended) but... my gut feel is you're probably OK. However I have no idea of the loads and how the different pieces are tied together sooo...

So, here's why I think you're OK. For starters the hole doesn't (appear) to go past the center-line of the tube. That's a big plus in preserving the integral strength of the tube. The second plus is the horizontal cross member welded above the hole. This should greatly reduce the chance of a side load causing the tube to buckle at the hole. If the parts you show in the details are mechanically tied (screwed or bolted) this should go a long way in increasing overall rigidity/strength.

What I would do in your situation? Get a piece of tube (10"-12") that will telescope over the tube with the hole. Split it lengthwise just slightly past the center-line to make a sleeve, place the sleeve on the tube with the hole, and slide it up, centering over the hole. Use clamps to make sure the sleeve is tight against the tube. Attach the sleeve with 1/4" SS sheet metal screws every 1" along the edge. Put the first screws in at the middle, opposite either side of the hole, and then work your way up and down each side and across the top and bottom. This will restore some of the integrity that was lost by cutting the tube, and if you seal the sleeve, it'll keep water out of it as well.

[garyfdl]

Originally Posted by billgewater

I bet many readers would be interested in just how you managed to drill such a large diameter hole so cleanly through the SS tube wall!
There have been a number of threads on SS drilling problems!

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.

[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.

[thruska]

The idea of a sleeve is not too terrible.
If it was me, I would place a gusset in the corners.
If access into the hole is required, simply scallop the gusset to suffice .
Or just let it alone and go sailing, much adieu about nothing ...

[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.

[GordMay]

The OP has S/S Tubing, not Pipe.
The wall thickness of tubing is measured in inches, or by standard gauge from 7 (heaviest) to 22 (lightest), which correspond to a range of wall thicknesses.
16 gauge tube wall thickness can vary between 0.060" through 0.065" (most common).

[hpeer]

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.

Vertical and horizontal loads are fine. The bigger loads will be because of the dink way out on the end if that beam. No dimensions on length but it looks to be 3 to 4 feet. That will have a strong downward moment but also a string TWIST or axial torque when the dink sways back and forth; port to starboard.

A while ago, maybe 3 years, there was a ling thread about a davit that failed. It was much lighter than this but it sheared a 1/4 20 bolt. What it came down to was the guy used an all thread bolt which was MUCH thinner through the threads than a shoulder bolt is through the shoulder.

Now a 1/4 20 bolts shear strength is about 1,200 pounds through the shoulder but 600 through the threads (Caution on those numbers, memory could be off). That installation was much simpler and without the long moment arm holding the dink.

The calculator I linked shows the KIND of calculation that needs to be done. But it also shows that this size hole in light steel is outside the normal parameters. That should give the OP cause to consider.

I think we are all winging it. Might be fine, I do not like the looks of it.

I know doing bridge construction the engineers would have a fit if we suggested drilling a hole in a beam. They would sometimes allow it if it was to he filled with a bolt essentially replacing the metal removed.

Look at it this way. Within that 1-1/8” of vertical tube the OP removed something like 30% to 40% of the metal. The entire structure has likely been weakened by a similar amount. If this weakening is OK why the heck was the original structure so heavily overbuilt?

Its an odd construction, lots to ask questions about. I am not wild about the solar and dink being supported out on that arm with only a but weld. No gussets vertically or horizontally.

IMHO this is not an “engineered” solution, its something someone stuck on without a lot of thought.