The 2025 Edition of ASME Section VIII, Division 2 brings a number of updates to high-temperature design practices. The changes to Part 5 expand the treatment of creep, clarify the role of primary and secondary stresses in ratcheting, and modernize the use of isochronous stress–strain curves for creep-buckling. For EPCs, owner-operators, and analysts working in high-temperature service, these updates represent a welcome alignment between legacy Code rules and the methods engineers actually use today.
Earlier editions of Div. 2 provided limited creep guidance and lacked the breadth needed for thorough and safe analysis. The 2025 updates expand that framework significantly:
The result is a more holistic alignment between how real materials behave at temperature and how the Code requires engineers to check them.
One of the most practical improvements is the renewed emphasis on isochronous stress–strain curves. Although familiar to engineers working under Section III (e.g., legacy N-47 / NB-3200 approaches), and ASME FFS-1/API 579 Chapter 10, they have not been widely used in many Division 2 workflows.
Isochronous curves define:
For example, 304 stainless steel at 950 °F exhibits noticeably different curves depending on whether the load duration is 1 hour, 1,000 hours, or 100,000 hours. At 1,000 °F, the entire family of curves shifts downward. The updated Div. 2 guidance ensures these relationships are properly incorporated when evaluating time-dependent deformation, rather than relying solely on instantaneous elastic properties. The use of the isochronous stress-strain curves is used solely in a nonlinear type analysis, where the material deformation exceeds the material yield at elevated temperature, such a buckling analysis.
This directly benefits designs where even modest creep strain accumulation must be controlled—such as heater coils, hot piping manifolds, high-temperature nozzles, or tube connections.
Perhaps the most engineer-friendly enhancement is the formal recognition of Bree-style primary + secondary load interaction diagrams. These diagrams have long been used informally by analysts to understand when incremental plastic strain (ratcheting) will occur, but the Code treatment has been scattered.
The 2025 Edition clarifies:
This clarity is especially helpful for pressure-bearing components that sit at the intersection of sustained pressure loading and cyclic thermal bending—where ratcheting, not fatigue, may govern.
B31.3 §304.7.2 increasingly directs analysts to Section VIII, Div. 2 non-linear methods for strain-limited evaluations. The 2025 improvements to Div. 2 therefore benefit piping assessments as well—particularly for:
The updated framework supports more consistent results across piping and vessel analyses and reduces the ambiguity that previously surrounded high-temperature screening.
Designers now have clearer guidance on when creep screening is sufficient and when full isochronous curve–based evaluation is required.
The updated Bree extension diagrams help engineers quickly determine whether a load combination will lead to incremental strain or simple elastic shakedown.
Adjustments to Part 5 allowables and load cases remove historical inconsistencies and streamline high-temperature assessments.
Division 2’s evolution continues to support workflows where elastic-plastic FEA, time-dependent material curves, and load-cycling simulations form the basis of design decisions.
The 2025 updates to ASME Section VIII, Division 2 Part 5 represent a significant modernization of creep, ratcheting, and high-temperature evaluation rules. By incorporating updated material behavior, clarifying primary–secondary load interactions, and synchronizing with piping methodologies, the new Edition enables more predictable and more defensible high-temperature designs.