Quick Release Structural Connection

[Ussuri]

Has anyone ever heard of a something like a 'quick release structural connection'

I have a small structural steel frame which will be deployed subsea. The structure is only temporary works and will need to be dismantled and removed. It cannot be removed in one piece because after its done the job it will be fouled by another structure.

Heres the catch, we are not using divers on this job, so the frame needs to be dismantled using remotely operated vehicles (ROV's).

I am looking for a method of dismantling a connection by pulling out a single pin for example. I can probably work up something unique but was wondering if there was something out there I could crib from. The connections are full moment connections, just to complicate things.

Any thoughts, inside or outside the box are appreciated.

 

[swearingen]

You could certainly do it with a single pin, although the connection would have to be huge if there are significant moments. I'm envisioning a pin with bearing plates above and below the pin. If the moment is positive, the lower bearing plate is in compression and vice versa. You could, of course, use two pins which would make a fine moment connection, but require twice the undersea work to remove them.

Don't forget that these pins may bind, so copious use of grease, the ability to use a surface winch to do the pulling, and a testing program are things to consider.

I saw a program about a super huge concrete rig support floated out into the North Sea from Sweden, I think. It used undersea pins and I remember them having trouble getting the ROV's to hook the quick release devices. The pins were removed by surface winches pulling long chains down to the connections.

 

[JStephen]

Perhaps consider something similar to a victaulic pipe coupling.

 

[Ussuri]

I had a look at their website, the snap joint coupling style 78 would work if it could take an applied moment. But looking at it I think it would struggle. I like the idea of it though.

Is there any specific product you had in mind. Most of the couplings had bolts which are not ROV friendly.

 

[valleyboy]

Ussuri

The SCI have developed a modular connection system called 'Quicon' - see the link beneath:-

http://www.quicon.com/web/contents.html

I note from the literature that only ultimate shears and tying forces are given, and as such I'm unsure whether moment connections can be achieved using this system.

 

[JStephen]

Well, instead of a bunch of big bolts, you have one or two little bolts. So next step is a suit-case like latch instead of the bolts. I was just brainstorming, haven't built anything like that.

Perhaps build the whole thing out of magnesium or similar alloys and just let it corrode away?

 

[4wilmar]

Are explosive bolts out of the question??? They seem to work for NASA and many web sites can be found on the net. Perhaps they might work for you.

 

[amorrison]

Twenty years ago NASA grade explosive bolts were used by some small manned submersibles. Some bolts worked - some did not. Hopefully better bolts are available in 2006.

Maybe what you need is some type of (structural) connection metal member that will dissolve or react to (salt) water and disappear.

Will the tempory structurs float to the surface after release or "fall" to the ocean floor?

Can it be designed so that it will break away at certain "designed in" "weak points" when given a tug from a surface cable ?

I would consider having two disconnect devices "in series"
so if one does not disconnect the second device device will.

Consider using a single disconnect device - as if you have one in each of the four corners and one disconnect does not work . . .

 

[amorrison]

See and browse here

http://www.under-water.co.uk/2001/022001weld.htm

 

[Ussuri]

I like the idea of exploding bolts, sounds cool, but I dont think I have any chance of using then just from the health and safety perspective. That said, there is no harm in asking.

The structure will sit on the seabed and be recovered to the surface after use. If I used a reactive alloy as the bolt material, how long would it take for a 24mm diameter bolt to dissolve? The frame may only be on the seabed for a matter of days before it needs to be removed.

 

[UcfSE]

Can you use bolts with a hole at the end and a cotter pin or a hitch pin? The pin can be pulled and the bolt slipped out of the hole.