An Overview of 2021 ASME Section VIII Code Changes

Outside of the new cone to cylinder calculations in Division 1 and Appendix 47 and the introduction of a certifying engineer and designer qualification, there are still many other changes to ASME Section VIII in the 2021 code changes. Here we will discuss how these changes impact the design and welding fabrication of pressure vessels and heat exchangers.

This blog overviews changes to Divisions 1 & 2, including:

B16.5 & B16.47 2020 Editions
Tube to Tubesheet Joint Options
Tubesheet Shear Stress Screening
Flange Change for Integral Flanges
Materials Change

ASME B16.5 & B16.47 2020 Editions

Currently, the 2020 editions for B16.5 & B16.47 are not officially allowed to be used with Section 8 Div. 1 or Div. 2. While this may seem odd, it’s actually not unfamiliar to the ASME code.

In the 2021 editions, Tables U-3(Div. 1) and 1.1 (Div. 2) now specify the 2017 editions of B16.5 and B16.47. The 2019 editions of Div.1 and 2 specified the 2013 edition of B16.5 and the 2017 edition of B16.47.

The reason the lag occurs is because BPV8 reserves the right to approve specific editions of references that contain acceptability criteria. ASME B16.5 and B16.47 contain pressure temperature ratings.

While it is not currently allowed to use the 2020 table standards with your vessels and pressure equipment fabrications, we expect that an implementing code case will be approved and published, allowing you to use these newer versions of the standards if you so choose.

NOTE: For those using DesignCalcs, you already have the option to use the 2020 editions of B16.5 and B16.47.

2021 ASME Tube to Tubesheet Joint Options

One of the easings of regulations comes from UW-20, Appendix A and the Division 2 counterpart of 4.21, which have expanded the tube to tubesheet joint configurations. There are now more explicit options. This means compliance will be easier.

ASME Tubesheet Shear Stress Screening changes for 2021

In addition, the tubesheet shear stress screening impacting heat exchanger design has been updated.

In 2019, both UHX and 4.18 were updated for Div. 1 and 2 to add a yield limit to the allowable tubesheet shear stress. At this time, however, the screening criteria wasn’t updated.

In the 2021 edition, however, this screening variable has been updated.

"Here are some design options to help you get a passing vessel design:"

Determine and use Ap and Cp.
For the operating cases, use the operating temperatures and pressures instead of design temperatures and pressures.
Use a thicker tubesheet.

Integral Type Flanges ASME 2021 Code Updates (Without a Tapered Hub)

In 2021, Division 2 implemented an explicit method to 4.16 for handling integral type flanges with a straight hub. In such a case, your g1 is equal to g0.

This revision essentially fills in an existing hole in Div. 2. Hub factors now support the case where g1 = g0. In addition, moment of inertia equations now support the case where g1 = g0 (for when you’re evaluating external loads).

Now, consider this relative to hub factors. If you compare this change to the tables and figures in Section VIII, Div. 1, you’ll now see an agreement between them.

2021 ASME BPV VIII Material Changes

2021 saw the following material changes:

New materials added to Table UHA-23 / Table 3-A.3
New materials added to UNF-23.4
Optional calculation method for yield based on allowable stress

Materials Changes in Section II, Part D

As usual, there have been additions and deletions to the stress, yield, and ultimate tables. In addition, many of the materials now have new higher temperature values for both yield and tensile strength.

There have also been multiple note revisions, and common external pressure charts have been updated (e.g., Ext P charts: CS-1, -2, -3, -4, etc.).

More exotic materials have now been added to tables TE, TM, and PRD. These include:

25Cr-6Ni-Mo-N (TE)
47Fe-25Ni-23Cr-5.5Mo-N (TE, TM)
N08354 (TE,TM, PRD)

NOTE: A 200-page errata was released for Section II, D after the code books were published and made public.

Using Software to Comply with ASME Section 8 Code Changes

For many welders and fabrication managers, the time it takes to stay proficient with code changes can be quite a daunting task. Implementing the 2021 code changes across pressure vessel designs and welding fabrication will be the difference between manufacturing a compliant unit or a pressure vessel that isn’t compliant and fails to generate a profit.

As ASME Section VIII codes continue to evolve, how can you efficiently keep up with the changes? We developed DesignCalcs software at CEI with that same challenge in mind. As of February 2022, our software will be completely updated and have the 2021 code changes programmed in, meaning, when you design a pressure vessel with DesignCalcs, you can feel confident you’re designing to code. As an added benefit, the same software engineers who are responsible for DesignCalcs updates sit on ASME code committees. At CEI, we invest our time to help you save yours.