Neutron diffraction and neutron imaging residual strain measurements on offshore wind monopole weldments

Anaïs Jacob,Ali Mehmanparast,Joe Kelleher,Genoveva Burca

doi:10.1016/j.prostr.2018.12.085

Anaïs Jacob, Ali Mehmanparast + Show 2 more

Open Access

https://doi.org/10.1016/j.prostr.2018.12.085

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Abstract

Residual stress measurement is of fundamental interest in order to estimate the service life of engineering components and structures subjected to various loading conditions operating in different environments. Destructive and non-destructive techniques are used for the evaluation of residual stresses. Neutron diffraction, as a non-destructive technique, is widely used to measure the elastic strain component of a specific atomic plane from which residual stresses can be calculated. Neutron imaging is an alternative technique which enables residual stresses to be measured through strain mapping of the area of interest. In this study, neutron diffraction measurements were performed in conjunction with neutron imaging to evaluate residual strains in a compact tension, C(T), specimen extracted from a welded plate made of S355 structural steel. Neutron diffraction and imaging are two complementary techniques which have been employed in this work by performing measurements on the Engin-X and newly developed IMAT instruments, respectively, at the Rutherford Appleton Laboratory. Neutron diffraction residual strain measurements in all three directions were conducted within the Heat Affected Zone (HAZ) of the weld area whereas longitudinal residual strains were measured using the neutron imaging technique. A comparison of the neutron diffraction and neutron imaging preliminary results has shown that neutron imaging can provide acceptable measure of residual strains compared to those of obtained from neutron diffraction. The results have been discussed in terms of the possible sources of error encountered in each measurement technique and the accuracy of each technique against the other.

Highlights

KWeywelodrdesd: HjoiginhtPsreasrseurwe TidurebliyneuBsleadde;inCrteheep;oFfifnsitheoErleemreennteMweathbolde; e3DneMrgoydesl;eScitmourlattoiosnu. pport offshore wind turbines
Neutron imaging is a volumetric measurement applied on a plane to measure residual strains in a direction normal to the plane orientation, while neutron diffraction provides residual strains along two directions at a specific point
Seen in this figure is that the residual strain trends fall on top of each other when dd0 value is taken as the average of the neutron imaging data in the heat affected zone (HAZ) region and in the case where dd0 value comes from the strain balance of the same region in through thickness direction

Summary

Introduction

KWeywelodrdesd: HjoiginhtPsreasrseurwe TidurebliyneuBsleadde;inCrteheep;oFfifnsitheoErleemreennteMweathbolde; e3DneMrgoydesl;eScitmourlattoiosnu. pport offshore wind turbines. Offshore wind turbine monopiles are made of thick structural steel plates welded together in longitudinal. The full-length monopile is subsequently fabricated after circumferential welding of the individual cans. During this fabrication process, a significant amount of residual stress is expected to be stored in monopiles. Various techniques can be employed which are generally categorised as destructive (such as contour or hole drilling), as discussed by Kandil et al (2001), and non-destructive (such as X-ray diffraction or neutron diffraction), as presented by Ruud (1982). In order to accurately characterize the service life of offshore wind monopole welded structures, residual stresses should be measured and quantified. The focus of this study is use the neutron diffraction and imaging techniques to measure locked-in residual strains ( stresses) in compact tension, C(T), specimens extracted from monopole weldments

Specimen design and extraction

Test procedure

Neutron diffraction measurements

Neutron imaging measurements

Experimental results and discussion

Conclusion