Cutting Thin Stainless Steel tube with Fibre inside

[Yendor]

I have to cut a 4mm hollow stainless steel tube that contains 8 fibre optic cables. I need to remove about 1 metre of the Tube to expose the Fibres which are 125 microns in dia.

The tubes are normally plastic, and I run a stripping tool around the tube to score the outer part and then it snaps off with a little bending.

It is in an area that I cannot use any power or Battery tools.

I cannot get to the site until I am to do the job, so I don't know how much I have to play with to perfect a plan. I cannot obviously damage any of the fibres within the tube. It is on an Offshore Platform and in an EX area.

I have though of trying a small file to create a groove around the tube and then snapping it. Or even a Stanley blade. I can also try my existing stripping tool, and realise it will be useless after this.

There is apparently a tool for this type of Fibre cable with a stainless Steel tube, but it is £450, and since this is a one off, and the first time I have seen this type of tube in 7 years, I do not want to buy it.

Any thoughts on what might work?

[Andy Burns]

Even if a microbore type tube-cutter could close down as small as 4mm, don't suppose it'd like stainless ...

[Andy Burns]

Take one of these with you as a backup plan? should be cheap!

[newshound]

+1

Sounds very difficult to me.

4 mm OD or bore? What wall thickness? Do you really mean the fibres are 125 micron diameter, or is that the diameter of the glass which is then protected by a plastic sleeve. In which case, what's the OD?

Am I right in thinking that the fibres have a free end, so that when you have cut the tube diametrally in one place, you are sliding your 1 metre length off over the free end?

Stanley knife blade won't touch it. Triangular file would work, but pretty slow. Do you have reasonable access?

My first thoughts were something like a cordless dremel, either with a stone, diamond burr, or reinforced abrasive disk. But evidently you are not even allowed that.

I assume the £450 tool is something like a plumbers' tube cutter.

Another "gentle" way to attack it might be a very small air-abrasive or water-abrasive jet. The sort of thing which paleontologists use to extract fossils from sedimentary rock. But probably not a practical option here.

Not a job I would fancy. If there is a "proper" tool I would go for that and just factor it into the price (which I assume will not be small).

[Andy Burns]

If the client has to make such strict demands because of the area the fibre is in, they presumably expect to pay through the nose for someone equipped to meet them?

Sounds right for the actual fibre strands, depends if they're loosely or tightly buffered within the tube, what are the consequences of breaking any of them?

[Thomas Prufer]

It'll work on stainless, in principle at least. Recently cut a bit of thin-walled (1mm or less) stainless using a small Rothenberger cutter ("Minicut"). Like cutting copper, only I used less pressure and many more turns. Two cuts and the cutting wheel looked fine afterwards. I'd doubt if it would cut anything with a thick wall, though. Cheap enough to take on and hope, though.

Beware: It will "neck" the tubing, that is, make the ID smaller where it cuts.

Thomas Prufer

[Harry Bloomfield]

Thomas Prufer used his keyboard to write :

I would not expect the tube to pull off as a single one metre length, in will need to be done in several sections.

[newshound]

It will also leave a sharp edge on the inside, so great care needed when "snapping" and subsequent removal of the off-cut. Once removed, I'd slip a suitable sized sleeve over the fibres and inside the tube.

In fact that gives me an idea, might it be possible to slide in a metre-long length of sleeve so that you go past the cut point. That would protect and centralise the fibres at the critical times. Difficulty is going to be to find something the right size.

[Yendor]

4mm OD, about 1mm thick. the fibres have a 125 micron OD. This is including the protective coating on the fibre.

The Fibre has been cut, there are no free ends on cable. I am going to put free ends on it to repair it.

Have yet to see it. Speed is not an Issue, I will have as long as it takes

I would not have won the job if I added £450 to the quote.

[Yendor]

Loose tube. I have offered no guarantee on this, as they are unable to provide enough information. If it doesn't work it will involve pulling in a new 300m cable.

This is not an option

[newshound]

Yes, excellent point. That makes my "protective sleeve" idea more viable too.

[Yendor]

They do, The fibre Cable is called loose tube, and they lay inside the tube with some water repellent gel inside. Fibre is quite strong if handled correctly.

[Yendor]

As well as the fibres there is some gel inside the tube. Once the tube pulls off, The gel wipes off with IPA.

[newshound]

Bit of a gamble, then. Hope it comes off!

[Yendor]

The client is aware of the risks. I have found this on ebay

may work.

[Andy Burns]

If it goes wrong is there any risk to oil/gas production on the platform or others connected to it? Does the risk fall to them or you? You might want indemnity insurance that could cope with several £million/day of lost revenue ...

[newshound]

Can you get hold of a similar bit of tube to practice on before you go offshore?

I agree that cutter looks a good possible option, if you don't have a chance to practice I would take two or three with you. The cutting disks are *very* hard, and consequently brittle. I have known them to chip even on copper.

[dennis]

Don't forget that tube cutters like that compress the tube a bit and leave burrs on the inside which will damage the fibre if there is any movement.

[Fredxxx]

Hiring the right cutter seems the best bet.

I would expect a standard microbore cutter go down to the right size, if necessary with modification.

I would also carry out some trials beforehand on the same stainless pipe, ideally the same including fibres, perhaps a sample?

Next problem is the possible necking of the pipe and the sharp edge that can cut the fibre, how does the 'proper' tool overcome this problem? Is there an internal sleeve you can use to protect the fibre or a tool that can swell the end of the tube?

If it wasn't for the gel perhaps use Woods metal or less toxic alternative to stop the tube collapsing?

[damduck-egg]

I've got a couple of those knocking around , mainly used on brass for model making but have used them on SS in the past .

May work ? not the most accurate tool, Ok if you have another bit of tube to have another go with which you won't and the cut ends are almost always slightly smaller than the tube . . To be honest using a tool that cost less a pint of beer on what sounds like a fairly delicate task looks to be penny pinching too far. In fact I wonder if your being serious or spinning this group a yarn, giving you the benefit of doubt would you be better off with the smallest one on this list

Costs around £65 which is a lot more than the ebay cheapy but a lot less than the £450 you were talking about.

G.Harman