Topics: Code Updates

Cone to Cylinder Calculations – 2021 ASME Section VIII Code Changes

While Appendix 47 and the introduction of a certifying engineer are a major part of the 2021  ASME code changes, that isn’t the only part of the standard that is changing. Here we will discuss the changes to cone to cylinder calculations in ASME Section VIII, Division 1 and how this impacts the design and welding fabrication of pressure vessels and heat exchangers.

2021 Division 1 Cone to Cylinder Calculations

The changes in cone to cylinder calculations are contained in Division 1, Appendices 1-5 (internal pressure) and 1-8 (external pressure). Overall, these code changes mean it will be more difficult to get your cone to cylinder calculations to achieve compliance.


How to Determine the Delta Value

In the past, Delta was determined by a table, but now Delta is determined by an equation. This isn’t that big of a change, however, as the equation is very similar to the tables from 2019. This essentially results in a change in presentation.

The major change for calculating cone to cylinder junctions is the decrease of the available are value, Ae. 

Why the change? Why is the Ae value smaller in calculations for 2021? The reason is due to a correction in the use of the required thickness values. This is in the variables for t (cylinder required thickness) and tr (cone required thickness). Before these revisions, the required thickness values were not properly represented. With the new equations, the Ae result is properly reduced when considering larger t and tr values compared to the nominals.

This change in the equation will likely affect those doing vacuum-controlled or vacuum-only designs.


How to Comply with Required Reinforcement Calculation Requirements

There are a couple of methods you can use to ensure you are correctly calculating the cone to cylinder ratio.

  • Use a ring to reinforce the junction
  • Use Appendix 46 to jump to Part 4, Section VIII Div. 2 (NOTE: You can’t use a ring to reinforce the junction using this method)
  • Increase cylinder thickness or cone thickness


Cone to Cylinder Calculations Made Easy with ASME Div. VIII Software

Performing these calculations manually puts you at risk of non-compliance when fabricating your next pressure vessel. The easiest way to calculate the junction and ensure the proper reinforcement is with software dedicated to ASME Division VIII standards.

Start your trial

CEI crafted DesignCalcs precisely for this purpose. Make all your pressure vessels compliant with the new 2021 standards by using fit-for-purpose software that is updated rapidly, so you never have to worry about fabricating to an outdated standard. Request a free demo of DesignCalcs today.

Written by Mike Clark, PE

Mike earned his BSME and EIT in 2003 and gained his license in 2008. He has been actively involved with the ASME BPV code since 2004. At CEI, he is the lead advocate for DesignCalcs where he draws on his engineering background, code connections, and consulting experience to direct the software development and to explain the nuts and bolts of pressure vessel design.

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