Continue to Site

Eng-Tips is the largest engineering community on the Internet

Intelligent Work Forums for Engineering Professionals

  • Congratulations waross on being selected by the Eng-Tips community for having the most helpful posts in the forums last week. Way to Go!

Need a coupling for SS tubing with same OD as the tubing

Status
Not open for further replies.

KernOily

Petroleum
Jan 29, 2002
707
Guys I need a way to screw together short sections of 1/2" or 3/4" SS instrument tubing, each section being 4' long or so, and subject to the following constraints:

1) The OD of the coupling or connector must be the same OD as the tubing, i.e. a standard pipe coupling or pipe collar won't work
2) The ID must be open to pass liquid

An example would be the way that a rifle cleaning rod screws together - it has a smooth and flush OD at the coupling. These are not hollow though so the example stops there.

The coupling must be the same OD as the tubing because the entire assembly must pass through a packing gland. Do any of you know if a coupling/connector like that is commercially available? The Swagelok people were no help.

Thanks!
Pete
 
Replies continue below

Recommended for you

depending on what the pressure is for that service....you may have answered your own question...
If push comes to shove: calculate the wall thickness you need, get SS bar stock, bore through and thread it(male and female.
On the female side you may want to machine a groove for an O-ring at the end, don't do it at the end of the male portion if the o-ring is flushed by the flow you'll probably damage something.... but again you may have thought of this yourself.

All the commercially available connectors I know have an OD bigger than the OD of the instrument tubing.

Good luck
Saludos.
a.

 
You might want to try Allan Aircraft Supply Co in North Hollywood CA. The catalog I have is so old (I don't even want to say) they have specialized in unique applications like yours. Sorry I don't have a phone number or web link, but they do show up on "Lycos" and "Google" as one of Boeing's suppliers (still no link or phone no.)
 
Does the joint need to be disassembled in the future? If not, try orbital tube welding.
 
Guys thanks for your replies.

Yes this does need to be disassembled in the future. This is a cleaning lance for the on-line cleaning of an in-service low-pressure 16" line. The idea is to hook the end of the lance to a pressure washer, insert it into the packing gland, turn on the pressure washer, and then screw on more sections as needed. The max length needed is about 16' or so, so I would be screwing together three or four 4' long sections.

I thought about machining a fitting but the threads would have to be tapered to get any kind of an ID. A taperd thread would make a really thin section at the thread root and this has to hold 4000 psig or so. I still need to do the calcs - it might be OK since the tubing ID is only 3/4". Thanks!
Pete
 
Guys thanks for your replies.

Yes this does need to be disassembled in the future. This is a cleaning lance for the on-line cleaning of an in-service low-pressure 16" line. The idea is to hook the end of the lance to a pressure washer, insert it into the packing gland, turn on the pressure washer, and then screw on more sections as needed. The max length needed is about 16' or so, so I would be screwing together three or four 4' long sections.

I thought about machining some fittings, as was suggested, but the threads would have to be tapered to get any kind of an ID. A taperd thread would make a really thin section at the thread root and this has to hold 4000 psig or so. I still need to do the calcs - it might be OK since the tubing ID is only 3/4". Thanks!
Pete
 
Guys thanks for your replies.

Yes this does need to be disassembled in the future. This is a cleaning lance for the on-line cleaning of an in-service low-pressure 16" line. The idea is to hook the end of the lance to a pressure washer, insert it into the packing gland, turn on the pressure washer, and then screw on more sections as needed. The max length needed is about 16' or so, so I would be screwing together three or four 4' long sections.

I thought about machining some fittings, as was suggested, but the threads would have to be tapered to get a large enough ID through the coupling. A tapered thread would make a really thin section at the thread root and this has to hold 4000 psig or so. I still need to do the calcs - it might be OK since the tubing ID is only 3/4". Thanks!
Pete
 
You are on the right track with tapered and shouldered connections I believe. You might refer to API Spec 5CT Integral Joints or External Flush joints as used in wells (They do not include any standard for such small diameters or limited quantities). Also Minerals Exploration Drillers may use something similar. You will probably need to design, manufacture and test these connections with the help of an innovative machinist. I am concerned about your unsupported Length to Diameter ratio after entering the larger pipe. Anticipating the energy input and unbalanced forces, you may need to consider stabilizers or centralizers. Best Regards, and hope you've already completed all this successfully.
 
Suggest using cold drawn 1/8 hard tubing (available from Autoclave Engineering or HIP) with thick walls, threading ID, and having an ID coupler machined as described.
 
TEV - Thanks for your reply. Did you mean 18/8 tubing? Thanks!
Pete
 
No. I mean 1/8 hard tubing. That is, stainless steel tubing drawn to a higher tensile strength due to cold working.
 
Status
Not open for further replies.

Part and Inventory Search

Sponsor