Key Changes to ASME B31.1 From 2012 Through 2026
In 2013, I published Power Piping: The Complete Guide to ASME B31.1 through ASME Press, based on the Code through the 2012 edition. Although the foundational principles have not changed, subsequent editions introduced several significant additions and revisions. This article summarizes the more consequential changes to ASME B31.1 through the 2026 edition and is intended as a supplement to the book. The discussion begins with an overall summary and then identifies key changes edition by edition; it is not a complete list of revisions.
Most consequential ASME B31.1 changes from 2012 through 2026
The following table summarizes key changes since the 2012 baseline and explains their significance.
| Area | Principal change and significance |
|---|---|
| Operation and maintenance | Chapter VII expanded the requirements for Covered Piping Systems, including documentation of dynamic events, maintenance programs, qualified personnel, condition assessment, records, repairs, and rerating. B31.1 therefore addresses lifecycle integrity more explicitly for CPS, rather than concentrating only on design and construction. |
| NBEP quality management | The 2024 edition added Mandatory Appendix Q for quality-management programs for metallic Nonboiler External Piping Covered Piping Systems. It establishes requirements for the organizations responsible for NBEP-CPS work. |
| NBEP records | The 2024 edition added Mandatory Appendix R for documentation, records, and reports for metallic NBEP-CPS. |
| B31J | B31J became an optional alternative in 2018. In 2024, Mandatory Appendix D was deleted, leaving B31J as the required referenced method for flexibility factors and directional SIFs and stress indices within its scope. B31.1 separately prescribes certain axial-force treatments. |
| Multidirectional stress equations | The sustained, occasional, and displacement-stress equations were revised to recognize axial force and separate in-plane, out-of-plane, and torsional moments and indices. The revised equations use force and moment components that are readily available from modern piping-analysis software and can capture effects omitted by the former resultant-moment approach. |
| Creep strength enhanced ferritic steels | Requirements for Grade 91 and related CSEF materials were expanded, including cold forming, post-forming heat treatment, casting heat treatment, weld repairs, preheat, PWHT, and material-specific restrictions. These changes recognize the importance of metallurgical processing and heat-treatment control to long-term integrity. Changes to the CSEF steels allowable stresses and permitted grades and types were made during the period ending with the 2026 edition. |
| Nonmetallic piping | Appendix N made the nonmetallic and nonmetal-lined piping rules mandatory in 2014. |
| Metallic bellows | Mandatory Appendix P was added in 2018 for metallic bellows expansion joints, making the respective responsibilities of the piping designer and expansion-joint manufacturer more explicit. |
| Ultrasonic examination | Mandatory Appendix O was added in 2018 to provide fracture-mechanics-based flaw-sizing acceptance criteria, using measured flaw dimensions, in addition to the traditional amplitude-based ultrasonic acceptance criteria. |
| Flow-accelerated corrosion | The 2018 edition explicitly addressed flow-accelerated corrosion and reinforced the owner’s responsibility to identify susceptible systems. |
| Pressure testing | The 2024 edition generally requires joints to remain uncoated during pressure testing unless the owner permits otherwise, reducing the possibility that a coating will mask leakage. The 2020 edition added alternatives to hydrotest for NBEP. |
| Fitness for service | The 2024 edition references API 579-1/ASME FFS-1, with cautions for creep service and cyclic metal-loss assessments. |
| Wind and earthquake loads | The 2024 edition prohibits application of the ASCE 7 Allowable Stress Design reduction factor to wind and earthquake loads. Para. 120.2.4 was coordinated with this change by permitting the short-time allowable-stress increase in para. 121.2(j) for supplementary steel. This avoids reducing the demand while also increasing the B31.1 allowable stress for the same occasional event. |
| Boiler jurisdiction | Jurisdictional figures were expanded and clarified for several boiler arrangements, including HRSG desuperheater protection systems, firetube boilers, and locomotive boilers, keeping them current with Section I. |
| BEP conformity assessment | Boiler External Piping conformity-assessment provisions were coordinated with ASME CA-1 and QAI-1, and the former B31.1 Appendix J was deleted. |
| Materials | Material specifications, allowable stresses, temperature limits, weld efficiencies, bolting values, and table notes were repeatedly revised. |
| Alternative engineering methods | B31.1 made owner approval and documentation requirements more explicit when alternative, more rigorous engineering methods are used. |
| Designer | The 2024 edition formally added Designer as a defined party. |
| Low temperature service | The 2014 edition added requirements for low temperature service by adopting B31T. |
| Weld strength reduction factor | In 2018, the weld strength reduction factor W was incorporated directly into the applicable pressure-design equations, including the equations for bends. The factor accounts for the possibility that longitudinal or spiral seam welds may have lower long-term creep strength than the base material. When W is less than 1.0, the required wall thickness increases or the allowable pressure decreases. W is distinct from the weld joint efficiency or quality factor E or F. |
Edition-by-edition highlights
ASME B31.1-2014 Changes
The first major revision after the 2012 baseline included:
- Appendix N rules for nonmetallic and nonmetal-lined piping were made mandatory.
- Cold-forming rules were added for creep-strength-enhanced ferritic steels.
- Chapter VII was expanded to require documentation of dynamic events.
- Piping and pipe-support maintenance programs and personnel requirements were added.
- Preheat and PWHT rules were reorganized into tables.
- Added low temperature materials requirements by invoking B31T.
ASME B31.1-2016 Changes
The 2016 edition principally consolidated and refined the preceding technical changes:
- CSEF requirements were further developed, including controls for Grade 91 and C12A castings, heat treatment, and weld repairs.
- Cold-forming and post-forming heat-treatment requirements were revised.
- Alternative PWHT provisions for P-Nos. 1 and 3 and material-specific PWHT rules were refined.
- Weld details, NDE requirements, materials, and allowable-stress tables were revised.
- Chapter VII CPS requirements continued to develop.
- Added reference to B31J.
ASME B31.1-2018 Changes
The 2018 edition introduced several significant changes:
- B31J was permitted as an alternative source for flexibility factors and SIFs.
- Mandatory Appendix O was added for alternative ultrasonic acceptance criteria.
- Mandatory Appendix P was added for metallic bellows expansion joints.
- The weld strength reduction factor W was incorporated directly into applicable pressure-design equations, including bends.
- Flow-accelerated corrosion was explicitly addressed in Chapter III.
- Grade 91 and related CSEF material requirements were further revised.
- BEP conformity assessment was aligned with ASME CA-1 and QAI-1.
- NDE personnel qualification requirements were revised.
- New and revised jurisdictional figures were added, particularly for HRSG desuperheater protection.
- Owner approval and documentation requirements were strengthened for alternative, more rigorous engineering methods.
ASME B31.1-2020 Changes
The major development for piping analysts was the restructuring of the stress equations:
- Sustained, occasional, and displacement-stress equations changed to a multidirectional formulation.
- Axial force was incorporated explicitly.
- In-plane, out-of-plane, and torsional moments and their applicable indices or SIFs were treated separately.
- Sustained-stress indices were applied to fittings and branch connections.
- Added rules for repair of Covered Piping Systems.
- Added alternatives to hydrotest for NBEP.
These revisions replaced the essentially single-resultant-moment approach used in the 2012 through 2018 editions.
ASME B31.1-2022 Changes
The 2022 edition mainly refined and extended the 2020 framework:
- Use of multidirectional SIFs and sustained-stress indices was clarified.
- B31J continued to be permitted while the traditional Appendix D approach was retained.
- The relationship between SIFs and sustained-stress indices for branch connections was revised.
- Jurisdictional figures for firetube boilers and locomotive boilers were added or revised.
- Chapter VII included explicit provisions for CPS repair and rerating.
- Materials, welding, examination, and referenced standards were updated.
- Expanded standards permitted to be used for qualification of NDE personnel.
ASME B31.1-2024 Changes
The principal changes in the 2024 edition included:
- Mandatory Appendix Q was added for quality-management programs for metallic NBEP-CPS.
- Mandatory Appendix R was added for documentation, records, and reports for metallic NBEP-CPS.
- Mandatory Appendix D was deleted, leaving B31J as the required referenced method for flexibility factors and directional SIFs and stress indices within its scope.
- Joints generally must remain uncoated during pressure testing unless the owner permits otherwise.
- The ASCE 7 ASD reduction factor may not be applied to wind or earthquake loading.
- Supplementary-steel allowable-stress provisions were coordinated with the revised dynamic-load requirements.
- API 579-1/ASME FFS-1 was referenced, with cautions for creep and cyclic metal-loss assessments.
- Designer was added as a defined party.
- Gender-neutral terminology was adopted.
ASME B31.1-2026 Changes
The principal changes in the 2026 edition included:
- Permitted evaluation of occasional loads without considering creep.
- Moved Grade 91 Type 1 from the Code to a Code Case.
- Added considerations for hydrogen service.
Applying ASME B31.1 to your piping systems
The changes introduced since 2012 reflect the continued development of ASME B31.1’s requirements for power piping design and lifecycle integrity. Understanding these revisions helps owners and engineers review established practices against the applicable Code edition and identify where adjustments may be needed. Contact us today to discuss how Becht can help you evaluate and apply ASME B31.1 requirements for your power piping systems.
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