Large thread data

[EngineerPhil]

I want to use a UNC thread for part of my design of a pressure test rig. I can not find any information on the internet or in Machinery's Handbook regarding thread sizes greater than 6 inch.

I can't really use 6" as the OD of the pipe is 6.9" and I would loose to much strength by dropping down to this smaller OD, even just for a thread.

Can you get UN threads greater than 6"? I need to calculate tensile stress area and thread stripping areas. I need to protect against a worse case load of 215k psi.

Should I consider other thread types?

Any help greatly appreciated,

Cheers

Phil.

 

[swertel]

You can use UN threads larger than 6 inches, but you will have to "design" them yourself. In other words, the Machinery's Handbook and ASME standards show the geometry of a UN thread. You can use your OD of your tube as the major diameter and then calculate the pitch and minor diameters based on how many TPI you want. The designation of the thread will probably UNS since this probably will be a special thread size. On the face of the drawing, you may also want to call out the major, minor, and pitch diameters +/- tolerances along with the usual thread callout.

ASME Y14.6 has Screw and Thread Representation, but this is mostly how to show it on drawings.

Other thread types to look into that are more often large size would be ACME, SQUARE, and BUTTRESS which are commonly referred to as Power Screws.

 

[kalvin]

Spec. ASME B1.1 - 1989 covers thread specifications to 6"