Task Group 4: Non-linear Analysis


‘Technical Task Group’
Non-linear Analysis

Click here to view the Non-linear Design Rules.

Scope and Objectives of TG4

After a detailed existing Codes and Standards comparison [1], it was concluded that many Pressure Equipment Code have a Chapter on Nonlinear Analysis with limited information to perform the analyses and limited validation documents of their proposals. 2 particular Codes has been considered with particular attention: ASME BPV Code – Section VIII – Division 2 and AFCEN – RCC-MRx Code. Since this review a new Appendix has been proposed in AFCEN RCC-M Appendix ZC.
The major objectives of this Group are to review all the nonlinear rules used to design Pressure Equipment in different international Codes and the R&D State of the Art in order to propose:

  • a “recommended practice document” based on existing knowledge
  • a “complementary experimental R&D program“, developed with the support of EPERC and the European Commission, with a regular update if necessary of the previous document,
  • a “set of benchmarks” to assure usability of the proposed rules and that can be used as a set of typical applications

The “recommended practice document” will contain the different rules applicable, their detailed application, the material data required, the basic criteria, the Quality management required and all the associated validation (theoretical, engineering approaches and experimental validation).
Major failure modes and degradation mechanisms of Pressure Equipment will be considered:


  • Under monotonic loads: plastic collapse, plastic instability, local failure, buckling
  • Under cyclic loads: fatigue, shakedown
  • Consequences of potential crack in a pressure equipment: failure assessment diagram and reference stress approach, local approaches of rupture and “Master Curve Approach”, leak before break…
  • Particular cases of specific nonlinear analyses: openings and reinforced nozzle, elastic follow-up in piping system, seismic design, bolted flanges, bellows…

Creep conditions will not be considered in this first phase of this Project.


Click here to view the document “Non linear design rules”.

Please click here to read the report of the TG4 meeting of Milano, January 29th.