How are bolt lengths calculated in AutoPLANT Piping?

Overview

Bolt length calculations within AutoPLANT have changed and improved over the years. And with the AutoPLANT V8i releases, calculations for each bolt type have been documented in the help files for AutoPLANT Piping and SpecGen.

You can minimalize errors in bolt lengths by first understanding how bolts are calculated and then changing your spec values in the BOLT table accordingly.

 

Flange to Flange bolt lengths (stud bolts)

Flange to Flange connections DO NOT calculate the bolt length by default. The values are pulled directly from the spec using the BOLT_LEN field.

Note: This is why comparisons between wafer bolt connections and flange to flange connections are sometimes inconsistent. This is also why modifying the NUT_LEN and BOLT_XCESS fields do not changing bolt lengths.

You do not have to do this. But if you want, you can change the flange to flange connections so they are automatically calculated by the formula below. Here are the steps.

  1. In the Component Preferences toolbar, right click and go to “add component preferences”.
  2. Pick “BOLT_LENGTH_CALC” from the Result Field pulldown list and select OK.
  3. Changing the Calculate Bolt Length Preference from “no” to “yes” will force bolts to calculate Flange to Flange connections based on the formula below.

Stud Bolt Length = [Gasket Thickness] + [(Flange Thickness) x 2] + [(Nut length) x 2] + [(BOLT_XCESS) x 2]

Warning: Setting this value will also change how the long description is created. It will be based on the script method in order to update the bolt length rather than the LONG_DESCR field.

 

Wafer bolt lengths (stud bolts)

Now, wafer type connections are different. Wafer style flanged connections ALWAYS calculate.

Stud Bolt Length = Valve Length + [(Gasket Thickness) x 2] + [(Flange Thickness) x 2] + [(Nut length) x 2] + [(BOLT_XCESS) x 2]

 

To double check this is working correctly, you can type in GDATA at the command line and select each component to get their values.

  1. Hit F2 to see the AutoCAD Text windows.
  2. Type in GDATA and select the valve.
  3. Find the COMP_LEN field and record that value.
  4. Type in GDATA and select the flange.
  5. Find the FLNG_TH_M field and record that value.
  6. Type in GDATA and select the gasket.
  7. Find the COMP_LEN field and record that value.
  8. Type in GDATA and select the bolt.
  9. Find the NUT_LEN field and the BOLT_XCESS field. Record those values.

 

These values, plugged in to the formula above, will come up with a value. The value is then rounded up (usually to the nearest ¼”. That increment value is defined in the BOLT_INC field.

Example based on CS150 AutoPLANT spec using 6” main size:

  • COMP_LEN (2.3125) 6” RF 150LB Wafer butterfly valve
  • FLNG_TH_M (1) 6” RF 150LB WN Flange
  • COMP_LEN (0.125) gasket
  • NUT_LEN (0.625)
  • BOLT_XCESS (0.3125)
  • BOLT_INC (0.25)

Stud Bolt Length = Valve Length + [(Gasket Thickness) x 2] + [(Flange Thickness) x 2] + [(Nut length) x 2] + [(BOLT_XCESS) x 2]

2.3125 + [0.125 x 2] + [1 x2] + [0.625 x 2] + [0.3125 x 2] = 6.4375 (rounded to  6 ½”)

 


While flange to flange bolt lengths are ASME B16.5 standard, calculations when including wafer components are not. They are usually based on vendor recommendations for the valves, spacers, etc. I have personally ran several tests and compared the AutoPLANT V8i SS3 bolt calculation versus the recommended bolt lengths from various vendor catalogs online (i.e. Crane FLOWSEAL, SSI Equipment Inc, Media Valve Co. Inc. etc) and the AutoPLANT bolt lengths were accurate.

Of course, if you want to change the lengths, you may modify the BOLT_XCESS field to increase bolt lengths.

 

The following help file excerpt shows the formula used for all "calculated" bolt length connection types.

AutoPLANT Piping V8i SS3 Help File *EXCEPT*

For standard flange-flange connections:

Machine Bolt Length = [Gasket Thickness] + [(Flange Thickness) x 2] + Nut length + BOLT_XCESS

Stud Bolt Length = [Gasket Thickness] + [(Flange Thickness) x 2] + [(Nut length) x 2] + [(BOLT_XCESS) x 2]

 

For wafer type assemblies:

Machine Bolt Length = Valve length + [(Gasket Thickness) x 2] + [(Flange Thickness) x 2] + Nut length + BOLT_XCESS

Stud Bolt Length = Valve Length + [(Gasket Thickness) x 2] + [(Flange Thickness) x 2] + [(Nut length) x 2] + [(BOLT_XCESS) x 2]

 

For L.J. Stub End Flange + L.J. Stub End Flange connections:

Machine Bolt Length = [(Stub Thickness) x 2] + [Gasket Thickness] + [(Flange Thickness) x 2] + Nut length + BOLT_XCESS

Stud Bolt Length = [(Stub Thickness) x 2] + [(Gasket Thickness] + [(Flange Thickness) x 2] + [(Nut length) x 2] + [(BOLT_XCESS) x 2]

 

For L.J. Stub End Flange + Wafer Component + Ordinary Flange connections:

Machine Bolt Length =  [Stub Thickness] + [(Gasket Thickness) x 2] + [(Flange Thickness) x 2] + Nut length + BOLT_XCESS

Stud Bolt Length = [Stub Thickness] + [(Gasket Thickness) x 2] + [(Flange Thickness) x 2] + [(Nut length) x 2] + [(BOLT_XCESS) x 2]

 

After using the above formulas for calculating bolt length, a rounding off must be performed in order to match the manually calculated results with the results obtained from the script. The procedure is as follows:


Step 1:

X = (Bolt Length value obtained by above calculations) / BOLT_INC

The BOLT_INC field value can be obtained from the spec corresponding to the entry of the bolt placed.


Step 2:

[(Rounded off value of X) + 1] * BOLT_INC = Actual bolt length as calculated by script

Note that the rounding off of the X value in the second step involves the removal of all digits after the decimal, retaining only the original values before the decimal.