×
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

Mill tolerance equation confusion

Mill tolerance equation confusion

Mill tolerance equation confusion

(OP)
Hi
My company got some previous data sheet based upon ASME B31.3 for wall thickness calculation of a pipe. But I am confused by two set of equations to include the Mill tolerance with the minimum required wall thickness. Please find those two equations.
Tm=tm+ MT (expressed in mm)
or
Tm=tm÷[1-(MT/100)] ,If MT is given in percentage

The 1st equation is pretty straight forward adding the tolerance with the calculated wall thickness.

then why it is not similar with MT tolerance expressed in percentage?

Thanks for the help

RE: Mill tolerance equation confusion

Jomanchester,
For piping Mill tolerance is normally expressed as a % of the nominal thickness of a pipe. So when you calculate the required thickness to sustain the Design Pressure and add on the Corrosion allowance you end up with a thickness Tmin. The next step is to select a pipe thickness such that the nominal thickness Tnom less the Mill Tolerance is greater than Tmin.

i.e Tnom - MT >= Tmin or Tnom x (1 - MT/100) >= Tmin

So Tnom(or Required) > = Tmin / (1 - MT/100)

RE: Mill tolerance equation confusion

(OP)
That was perfect DSB123

CHEERS fellow

RE: Mill tolerance equation confusion

Its amazing how many people get this wrong, but always do a back calc, i.e. start with your nominal thickness, then subtract mill tolerance as a percent of nominal thickness, then subtract any fixed allowances such as corrosion and make sure you've got your design thickness.

You may only be fractions of a mm out but there's no excuse for getting this wrong.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

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!


Resources