The NeT Journey
Network title & mission
Accurate prediction and measurement of residual stresses and distortions in welds is an important part of assuring their short and long-term structural performance.
The mission of the European Network on Neutron Techniques Standardization for Structural Integrity (NeT) is to develop experimental and numerical techniques and standards for the reliable characterization of residual stresses in structural welds.
Partnership & resources
NeT was established in 2002 by its current Chairman, Dr A.G. Youtsos, and it has been operating since then on a "contribution in kind" basis from industrial, academic and research facility partners. It was founded and has since then been managed by the Neutron Methods group at the Joint Research Centre of the European Commission in Petten, the Netherlands. About 25 organizations are currently contributing to the network activities.
The formation of NeT is the result of many years (1995-2001) of European and international collaboration within funded and in-kind contribution projects on standardization (VAMAS TWA 20, RESTAND) and on nuclear component safety (VORSAC, BIMET, ADIMEW, ENPOWER and INTERWELD). NeT was founded based on the experiences from these activities and many of the partners in these projects have proceeded to become members of NeT as well.
The ISO International Standard 21432:2019 on determining residual stresses by neutron diffraction has been supported by NeT studies, which have also contributed to ISO/TS 18166:2015 on numerical welding simulation.
Two of the NeT studies (TG1 and TG4) have been adopted as validation benchmarks for the weld residual stress simulation guidelines incorporated into the R6 defect assessment procedure.
Each problem examined by the network is tackled by creating a dedicated Task Group (TG), which undertakes specimen design and manufacture, and measurement and modelling round robin studies and the interpretation of their results.
Scientific publications, contributions to PhD work etc.
The NeT research activities and their results are published in ca. 125 academic publications and have contributed to more than 15 PhD degree theses in relevant scientific disciplines. Two special issues of the International Journal of Pressure Vessels and Piping have been published in January 2009 and July 2018 covering the results and the interpretation of NeT Task Groups 1 and 4, respectively.
Lessons learned, achievements
Perhaps the most significant NeT achievement is that it has played an important role in the development of reliable predictive numerical models and the verification of their results, based on sound measured residual stress test data obtained primarily by neutron diffraction.
The NeT round robins are amongst the most comprehensive ever performed, involving strict control of specimen manufacture, detailed record keeping, multiple residual stress and distortion measurements using different instruments and techniques, extensive materials characterization, and comprehensive simulation campaigns.
Although NeT studies to date have been driven by the need to underwrite the safety and performance of critical welded or cast components in the nuclear industry, their outcomes have widespread industrial relevance.
This is also underpinned by the view of the industrial partners who have confirmed that NeT has improved significantly their confidence in the different residual stress measurement techniques, including neutron diffraction, and also their understanding of the capabilities of these techniques. Furthermore, the industrial partners pointed out that on various occasions NeT had provided them the means to validate their numerical stress predictions in response to plant life management and nuclear safety issues.