×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Pipe Threads NPT versus ANPT

Pipe Threads NPT versus ANPT

Pipe Threads NPT versus ANPT

(OP)
Using the standards ASME B1.20.1 for National Pipe Taper (NPT) threads and SAE AS71051 for Aeronautical National Pipe Taper (ANPT) threads, is it practical to manufacture NPT threads and check them as ANPT threads?  Can NPT and ANPT L1, L2, and six-step gages be interchanged or must they be used as sets? Example, use an NPT L1, ANPT L2, and ANPT six-step to check ANPT threads?

My vendor is creating "sharp" external pipe threads in order to satisfy all three ANPT gages. The sharp external threads are (I believe) causing an interference issue when mating with other ANPT and NPT threads because the internal thread roots can be shallower.   

We didn't have this great of a galling issue before the ANPT threads became a requirement.  Also, corresponding with the sharp external threads, external threads that gage ANPT correctly and are assembled one time will not gage ANPT. The once-assembled threads allow the six-step to fall too far.  Any comments??

These connections are make and break, meaning the threads are intended to be used several times without damage.

RE: Pipe Threads NPT versus ANPT

awol,

Sorry I don't have an answer because I have the same question!  I have compared both standards and can't find any difference between NPT and ANPT threads.

RE: Pipe Threads NPT versus ANPT

(OP)
After some investigation, here is what I found. NPT and ANPT threads are made the same way. The ANPT threads are required to meet two additional gaging methods, the L2 and the 6-step. There is no difference in the NPT L1 gage and the ANPT L1 gage. No such gages as L2 and six-step for NPT.

The L2 gage check the 4th, 5th and 6th threads , I believe.

While this sounds very exact, I have discovered that threads will gage differently after being assembled a few times, near to the point of failing the inspection. Why? Are there machining burrs that "fool" the gage during inspection that are removed during assembly? Or are the threads and material 'yielding'?

The sharp threads seem to be correct, the deep roots are correct.  I have determined my joint issue is the type of thread sealant, not the thread profile. NPT threads should not be the first choice for a make-and-break appliation. Teflon tape should not be used if the joint is to be disassembled. The ductile iron got some bad publicity at my company, but I believe the material is OK. -awol

RE: Pipe Threads NPT versus ANPT

What is the difference between NPT and ANPT threads?  Manufacturing? Gaging?  One type of thread better than another?

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members! Already a Member? Login


Resources

eBook - 10 Reasons to Choose CATIA on the Cloud
To compete in today’s fast-paced and competitive market, smaller and newer firms need a powerful platform that will enable them to compete with bigger players, without the heavy investments needed in computer hardware, software and personnel. Download Now
White Paper - Smart Manufacturing for Electronics
This white paper describes a transformative approach to electronics manufacturing made possible by the addition of Mentor Graphics to the Siemens family. It describes a completely digitalized strategy that supports both printed circuit board (PCB) and mechanical design and manufacturing, uniting the entire product lifecycle – from idea and production to customers and back. Download Now

Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close