TG8: 5-Pass Slot Dissimilar Weld (Ni alloy) on Ferritic Steel

 

NeT TG8 examines a steel plate (French grade 18MND5) containing a five pass "slot" weld made with Ni base alloy (Alloy 52) consumables. The Task Group has been organized to address welding repair issues. The TG8 round robin specimen is closely based upon the TG4 design, except for the plate thickness that is increased to 30 mm for more self-clamping conditions and to reduce distortions. It thus presents all the advantages and challenges of the TG4 specimens, namely, the generation of a complex 3D residual stress distribution in a compact, portable specimen that is amenable to rapid measurement of residual stresses by diverse techniques, with a significant volume of weld metal that undergoes multiple high temperature thermo-mechanical load cycles. The use of a nickel-based alloy as filler metal adds considerable residual stress measurement challenges, while this configuration undergoes a complex mismatch behaviour with the base metal where phase transformations and tempering effects occur in the Heat Affected Zone.

The benchmark specimens have been manufactured and the welding process thoroughly characterized; materials characterization has reached the stage where finite element simulation can be performed, and the residual stress measurements round robin is in progress.

The TG8 specimen consists of a plate with a central groove filled with five weld beads in two layers, with two beads in the first layer and three beads in the second layer. The groove and plate dimension before welding are shown in Figure 1: Each plate is 30 mm thick, 200 mm long and 150 mm wide. As-welded plates and post weld heat treated plates were manufactured. Metallography, microscopy, and hardness measurements are being conducted on test pieces and sections extracted from these plates.

The residual stress measurement and simulation round robins for TG8 are ongoing [1]. What is presented here is therefore a snapshot of the behaviour of the TG8 specimens. A typical finite element mesh developed for a moving heat source analyses to simulate residual stresses in the current zone (plane B) of the TG8 specimen is shown in Figure 4.

Figure 5 shows measured stresses along the BD line, at the intersection between the B and D planes. The agreement between stresses measured by the Contour Method and by neutron diffraction is generally very good.

  1. V. Robin, S. Hendili, J. Delmas, J. Draup, Q. Xiong, M.C. Smith, A. Paget, NET PROJECT TASK GROUP 8 AN INTERNATIONAL BENCHMARK ON RESIDUAL STRESS ASSESSMENT FOR WELDING REPAIR, PVP2022 85083, Proceedings of the ASME 2022 Pressure Vessels and Piping Conference PVP2022 July 17-22, 2022, Las Vegas, Nevada, USA.

Fig. 1. The dimensions of THE TG8 mock-up

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Fig. 2. Sketch of TG8 specimen showing the co-ordinate system used of the residual stress measurements. Line BD is defined as the intersection between planes B and D

ON THE RIGHT: photograph of specimen top surface

Fig. 3. Metallography and hardness mapping in the as-welded condition

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Fig. 4. 3D simulation, PLANE B and BD LINE (L. Depradeux, EC2M)

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Fig. 5. Contour Method AND Neutron Diffraction results, BD line

(R.C. Wimpory (HZB), G. Trespeuch (SONATS)).

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