×
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

P-T Combination giving the max wall thickness
2

P-T Combination giving the max wall thickness

P-T Combination giving the max wall thickness

(OP)
Is there a combination of pressure and temperature that will give the largest wall thickness by the B31.3 wall thickness equation? The P-T ratings are from B16.5 for a class 300 A105 flange.

A Chiyoda pipe class document for class 300 gives the combination of 398.9 deg C and 35.3 bar for A105 flange based on 1996 editions of B16.5 and B31.3.

The attached graph plot shows the result of calcs based on B16.5-2003 and B31.3-2004, I did. The y axis of the chart shows the thickness figure (w/o multiplying with the diameter). The x axis is the temperature in deg C. Allowable stress for A105 is used (wall thickness of the flange hub). The thickness figure is calculated for the allowable flange rating pressure for each temperature, using the corresponding allowable stress at that temperature.

I was thinking that the figures would shows a consistant increase of the thickness figure because of the drop in allowable stress. The drop in rating pressure is not that significant. The plot is close to this even if I use the 38 deg C rating pressure for the temperature range. The plot is strange in that it has more than one maximums. It does not seem to be an error in my calcs.

RE: P-T Combination giving the max wall thickness

B31.3 allows fitting design,
(b) A flange may be designed in accordance with the
BPV Code, Section VIII, Division 1, Appendix 2, using
the allowable stresses and temperature limits of the B31.3
Code.

But I don't have BPV-VIII, so it would be helpfull if you gave the formulas you were using.  I don't have your Chiyoda document either.

If it was straight pipe, which it isn't, B31.3-2008 p304.5.1 says you can design like this,

A105 allowable stresses at temperatures 100 to 800 are,
100  200  300  400  500  600  650  700  750  800  
23.3 21.9 21.3 20.6 19.4 17.8 17.4 17.3 14.8 12.0

B31.3-2008 p304.1.2 Straight Pipe Under Internal Pressure
(a) For t < D/6, the internal pressure design thickness
for straight pipe shall be not less than that calculated
in accordance with either eq. (3a) or eq. (3b):
t = PD/(2(SEW+PY))
t = P(d+2c)/(2(SEW-P(1-Y)))
(b) For t ≥ D/6 or for P/SE > 0.385, calculation of
pressure design thickness for straight pipe requires special
consideration of factors such as theory of failure,
effects of fatigue, and thermal stress.

For those formulas, the curve would only vary with the allowable stress, so it would look exactly like that plot of the allowable stress with temperature.

**********************
"Pumping accounts for 20% of the world's energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies) http://virtualpipeline.spaces.live.com/

RE: P-T Combination giving the max wall thickness

(OP)
Thanks BigInch,

The Chiyoda document merely gives pressure temperature combinations from B16.5 which will result in the maximum pipe wall thickness. This is used to select the pressure and temperatures to be used as basis for the pipe classes.

Yes the thickness formula is the formula (a). E and W are 1.

You are right in that the thickness profile follows the allowable stress profile. It does so if I use the B16.5 38 deg C pressure of 51.1 bar (g) for all temperatures along the x-axis. The Excel chart had not refreshed to the changed value.

However, If I use the B16.5 values of pressure in the thickness formula, corresponding to the x-axis temperatures, the plot has the profile like what I have posted. This is what I was trying to find out. Whether there was such a maximum. The B16.5 allowable pressures reduce with temperature and so does the allowable stresses. It could possibly have been a flat line, which is not. It may, if the plot had more data and viewed at a lower scale. I am not convinced about what is there in the Chiyoda document.

 

RE: P-T Combination giving the max wall thickness

I managed to find the BVP equation,
As long as 2Ytm is scaled with diameter, should be linear.
--------------------------------------------------
ASME Section III, Class 2 NC (1980)
Allowable Pressure
The allowable pressure for straight pipes and bends is calculated from Equation 5 of
NC-3641.1.
P = 2SEtm/(D − 2Y tm)
where
P = allowable pressure
S = allowable stress
E = joint factor (input as material property)
tm = minimum required thickness, including mechanical and corrosion allowances
= t× (1 − mill tolerance/100) − corrosion allowance
t = nominal pipe thickness
D = outside diameter
d = Inside diameter
Y = Pressure coefficient
= 0.4 for t < D/6
= d/(D + d) for t  D/6

Maybe this helps too.
These show some nonlinearity, but nothing like you have.
At high temp, they go very nonlinear.
TABLES
http://www.lightmypump.com/flange_classes.pdf

**********************
"Pumping accounts for 20% of the world's energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies) http://virtualpipeline.spaces.live.com/

RE: P-T Combination giving the max wall thickness

(OP)
The Sec III allowable pressure formula for pipe under circumferential stress should give linear or probably a slope in only 1 direction. The allowable pressure listed in B16.5 is based on a flange calculation and the limiting pressure determined thereby.

The temperatures used in my calcs is upto 425 deg C with the single bar caution on the allowable stress tables of B31.3 Appendix A.

The lightmypump link tables are the previous version of those tables.

I had the Chiyoda table and Excel charts attached in the earlier post. Did you have a look at them?

RE: P-T Combination giving the max wall thickness

Only the graph is there.

**********************
"Pumping accounts for 20% of the world's energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies) http://virtualpipeline.spaces.live.com/

RE: P-T Combination giving the max wall thickness

(OP)
The other doc is attached in the 3rd post of this thread.

RE: P-T Combination giving the max wall thickness

I think if you use the correct formula,
P = 2SEtm/(D − 2Y tm), it will work.   

**********************
"Pumping accounts for 20% of the world's energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies) http://virtualpipeline.spaces.live.com/

RE: P-T Combination giving the max wall thickness

(OP)
The P expression is merely a rewrite of tm that I have used. Therefore it will give the graph with the slope in one direction.
Moreover it does not make sense to use a formula to determine P by a formula when it is already known from B16.5.

RE: P-T Combination giving the max wall thickness

Of course.  If you're buying a flange, yes you already know the answer, so just buy your required pressure rating and you get the thickness you need from the manufacturer.  If you're designing a flange, you've got to calculate the thickness first.

**********************
"Pumping accounts for 20% of the world's energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies) http://virtualpipeline.spaces.live.com/

RE: P-T Combination giving the max wall thickness

svi (Mechanical)
Please review PIPE CLASS COMPONENT SOFTWARE BY

Re d-Bag Softw are
Rotte rdam s e w e g 183c
2629 H D De lft
Th e Ne th e rlands
Te l: + 31(0)15 268 2504
Fax: + 31(0)15 268 2530
info@ re d-bag.com
h ttp://w w w .re d-bag.com


THIS MAY SAVE YOU TIME, MONEY, AND YOUR JOB

L S THILL

RE: P-T Combination giving the max wall thickness

(OP)
Software can't help. I am looking for the basis of something.

RE: P-T Combination giving the max wall thickness

(OP)
I had word from Chiyoda.

At 399 deg C the thickness is maximum using the B16.5 rating pressure of around 34.7 bar (g).
This is an optimisation method for pipe wall thickness calculation for pipe classes. Instead of having to use the full rating pressure (class 300) of 51.1 bar (g) corresponding to 38 deg C, thickness is calculated at the 'severe P-T combination'.

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