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International Journal of Pressure Vessels and Piping 93-94 (2012) 17e21

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International Journal of Pressure Vessels and Piping

journal homepage: www.elsevier .com/locate/ i jpvp

Influence of welding passes on grain orientation e The example of a multi-passV-weld

Jing Ye a, Joseph Moysan b,*, Sung-Jin Song a, Hak-Joon Kim a, Bertrand Chassignole c, Cécile Gueudré b,Olivier Dupond c

a School of Mechanical Engineering, Sungkyunkwan University, 300 Chunchun-dong, Jangan-gu 440-746, South Korea1bAix-Marseille Université, Laboratoire de Mécanique et d’Acoustique, site du LCND, Av. Gaston Berger, 13625 Aix en Provence, France2cDépartement MMC, EDF R&D, Site des Renardières, 77818 Moret-sur-Loing, France3

a r t i c l e i n f o

Article history:Received 22 July 2011Received in revised form20 January 2012Accepted 6 February 2012

Keywords:Austenitic weldGrain modellingInfluence of welding pass orderUltrasound

* Corresponding author. Fax: þ33 4 42 93 90 70.E-mail addresses: yejing@skku.edu (J. Ye),

joseph.moysan@univ-amu.fr (J. Moysan), sjsong@skkuskku.edu (H.-J. Kim), bertrand.chassignole@cecile.gueudre@univ-amu.fr (C. Gueudré), olivier.dupo

1 Tel.: þ82 31 290 7493.2 Tel.: þ33 4 42 93 90 52.3 Tel.: þ33 1 60 73 63 09.

0308-0161/$ e see front matter � 2012 Elsevier Ltd.doi:10.1016/j.ijpvp.2012.02.007

a b s t r a c t

The accurate modelling of grain orientations in a weld is important, when accurate ultrasonic testpredictions of a welded assembly are needed. To achieve this objective, Electricité de France (EDF) andthe Laboratoire de Caractérisation Non Destructive (LCND) have developed a dedicated code, whichmakes use of information recorded in the welding procedure. Among the welding parameters recorded,although the order in which the welding passes are made is of primary importance in the weldingprocess, this information is not always well known or accurately described. In the present paper weanalyse in greater detail the influence of the order of welding passes, using data obtained from the Centrefor Advanced Non Destructive Evaluation (CANDE), derived from a dissimilar metal weld (DMW) withbuttering. Comparisons are made using grain orientation measurements on a macrograph.

� 2012 Elsevier Ltd. All rights reserved.

1. Introduction

Austenitic stainless steels are widely used in the nuclearindustry due to their high corrosive resistance and excellent creepproperties over a wide range of temperatures. The inspection ofaustenitic material welds using classical focused transducers orphased array transducers may be difficult, because the grainorientation induces ultrasonic beam deviations and splitting. Asa consequence, an accurate description of the material is a neces-sary precondition for reliable results to be obtained in ultrasonicmodelling and testing.

Several material models use geometrical laws, derived from theanalysis of macrographs [1e8], to describe grain orientation. Overa period of several years, a more complete approach to themodelling of grain orientation has been developed by EDF andLCND. This has been encoded into a software package referred

joseph.moysan@univmed.fr,.edu (S.-J. Song), hjkim21c@edf.fr (B. Chassignole),nd@edf.fr (O. Dupond).

All rights reserved.

to as ‘MINA’, which makes use of information recorded in thewelding notebook, the modelling of solidification mechanisms,and parameters extracted from the weld macrographs [9,13].The validation of MINA has been presented in several papers[10,11]. The welding pass order was considered to be a knownparameter in previous studies of academic welds. Four mainphenomenological parameters, chosen on the basis of prior expe-rience, are needed to run the MINA code: firstly, the vertical andlateral remelting parameters allow the remelting of passes to bedescribed, and secondly, the two angles describing the pass incli-nation are needed [10]. However, in real welds, due to the diffi-culties associated with manual welding, other parameters couldalso modify the passes deposition process. Various modificationscould occur, without been reported in the welding notebook, sincethe welder may adapt the pass order to the variations inherent inthe welding process, such as the deposition rate and grindingprocedures between passes. A slight inclination of the pass layercould lead to two different descriptions of the pass order, as shownin the example of the weld specimen (white arrow) in Fig. 1.

In the present paper, we investigate the feasibility of using theMINA model to overcome this difficulty, and the degree of sensi-tivity of the modelling process.

We compare the two most realistic welding pass orders, andtheir influence on grain orientation. The grain orientations pre-dicted by our model are compared with those simulated by the

Fig. 1. Macrograph of a real specimen, with buttering and a grid overlay for grain orientation measurements.

Fig. 2. Description of the dissimilar metal weld.

J. Ye et al. / International Journal of Pressure Vessels and Piping 93-94 (2012) 17e2118

Modified Ogilvy model [14], and with those measured on thewelding samples. In [14], Ye Jing et al. describe an optimizationalgorithm used to fit Ogilvy’s parameters to our weld specimen.The novelty of this approach lies in their use of two sets ofparameters, in order to take asymmetrical orientation distributionsinto account.

The MINA parameters are firstly evaluated using macrographanalysis, thenwe explain how order of passes could be modelled. Ina third stepwe comparemodelling results (local grain orientations)with macrograph measurements.

2. Evaluation of MINA parameters

Three physical phenomena are involved in the MINA model:epitaxial growth, the influence of temperature gradient, andcompetition between grains. Epitaxial growth implies that, at everypoint, the melt metal adopts the crystallographic orientation of theunderlying pass. The grain direction could change during growth,but the crystallographic orientation would be maintained. Grainshave a propensity to align themselves in the direction of thetemperature gradient. In the case of multi-pass welding, there arelocal temperature gradient direction changes due simply to theshape of the welding pool. There is competition between grains, asthey grow preferentially if one of the <100> crystallographic axesis aligned close to the direction of the temperature gradient. TheMINA model takes this competition into account, using a specificiterative calculation, which depends on the modelling scale [10].

In order to take overlapping of passes into account, two inputparameters, determined by analysing the weld macrograph, areused in MINA: RL and RV, which represent the lateral and verticalremelting rates of the current pass, respectively [10]. Following theparameter used to describe the welding pass order, these twoparameters are the most important. Average values could also beenobtained from other welds, using a similar welding process. Frommeasurements of the weld made at CANDE, the average values of RLand RV are respectively 0.29 and 0.44, which is in agreement withprevious studies using the SMAW process [10].

The observation of the macrograph of a multi-pass weld showsthat the passes have a parabolic shape and are tilted. Two otherMINA parameters are used: qB describes the angle of inclination ofthe pass towards the edge of the chamfer, and qC describes theangle of inclination of a given pass with respect to the previouspass. In the MINA code, this phenomenon is taken into account by

rotating the direction of the temperature gradient, with no changein the geometric shape of the pass. The average value of qB is 12�,and the average value of qC is 7�. These are average values, obtainedfrom approximately ten to twenty measurements, from a total ofthirty-three passes. There is no tilt anglewhen the pass is depositedbetween the chamfer and a previous pass, or between two previouspasses. The MINA code produces a matrix of grain orientation. Thematrix size depends on the chosen scale and on the chamferdimensions.

3. Pass order analysis

The dissimilar metal weld (DMW) specimen under investigation(Fig. 2) has a V-shaped chamfer filled with 33 weld passes by usingthe filler material made of EniCr-Fe-3 (Alloy 182). The weldingprocess of Groove is Shielded metal arc welding (SMAW), and thewelding position is flat position. The welded zone is 22.7 mm thick,the top width is 40 mm and the weld root is 2 mm. The basematerial of one side of the weld is SA508 Gr.3, which is a kind ofmild steel; the base material of the other side of the weld is SA240tp304. This weld also embodies a buttering part in between theweld (austenitic steel) and mild steel. The buttering by GasTungsten-Arc Welding (GTAW) is made of is ERNiCr-3 (Alloy 82)(Inconel 600). Like some of the works on DMW, the materialproperty along the axis normal to the inspection plane is assumedto be homogeneous, for along this axis there’s only one pass duringwelding [9]. Except the SA508 Gr.3, EniCr-Fe-3, ERNiCr-3 and SA508Gr.3 share the same elastic constants of material property as

J. Ye et al. / International Journal of Pressure Vessels and Piping 93-94 (2012) 17e21 19

austenitic stainless steel. The sound velocities of mild steel areCL ¼ 5900 m s�1 and CT ¼ 3196 m s�1. The elastic constants of thetransversely isotropic austenitic stainless steel are c11 ¼ 241.1 GPa,c12 ¼ 96.916 GPa, c13 ¼ 138.03 GPa, c33 ¼ 240.12 GPa,c44 ¼ 112.29 GPa, and the mass density is 7890 kg m�3. The multi-pass weld was composed of 33 runs.

The electrode diameter was 4 mm for all the passes, and thewelding speed varied between 13 and 16 cm/min for the first pass,and 15 and 19 cm/min for the following passes. The inter-passtemperature varied between 30 �C and 110 �C. From the macro-graphs (Fig. 1), it can be seen that the pass shape is parabolic, whichis in agreement with the assumptions made in MINA. Both theremelting parameters and the electrode tilt angles could beconsidered to be virtually constant. It is also reasonable to considerthe grains to be tilted only in the plane transverse to the weldingdirection, since the grains appear clearly on a transverse macro-graph. This confirms that there are no significant 3D effectsmodifying grain growth, when the welding procedure is made ina flat position. The welding procedures and macrograph thuscomply with the hypotheses used in the MINA code [10].

In addition, the CANDE welding notebook indicates the numberof layers and the number of passes used for each of the 10 layers. Inthe flat welding position, there are three possible classical weldingsequences. The first of these is referred to as being parallel whenthe passes are deposited for each pass, from left-to-right or right-to-left. The second sequence involves the use of ‘alternate’ passes(left-to-right then right-to-left), and the third possibility is that ofthe ‘American’ sequence, involving the side to side deposition ofpasses (see the pass order shown in Fig. 3). In Fig. 3 the shape of thepasses is shown qualitatively, in order to indicate the pass position.The notebook indicates that the weld was deposited from right-to-left, with the exception of the 8th layer, which was welded fromleft-to-right. This pass order is referred to as ‘Solution 1’ in Fig. 3.

During a manual welding process, variations may arise. In thecase of the weld described here, after careful examination of themacrograph, two observations can be made. The macrographanalysis reveals that, due to the slight slope of the passes, these arenot aligned horizontally. Secondly, the change in pass order at the8th layer means that the 18th pass could be considered to be a passof the 7th or the 8th layer. The pass order can thus be simulatedusing two different descriptions: Solution 1, which is closer to thenotebook, and Solution 2 which takes the second approach tointerpretation of the “slope” induced by manual welding intoaccount.

Three orders of passes (or passes sequences) are considered intheMINAmodel to reproduce real welding conditions. Two of themare classical order of passes: continuous sequence from one side to

Fig. 3. Materials, weld configuration and two solutions for welding pass order. Passorder: L: left-to-right; R: right-to-left, US: “american way”.

the other, beginning on the right side or on the left side. The thirdone, called the Americanway in previous works [10,13], refers to analternate pass deposit. A pass is deposited on one side, the next isthen deposited on the opposite side. In this welding procedure, thefinal pass of the layer is in the centre of the weld and not on one ofthe two sides. In Fig. 3, the symbol “US” at the beginning of the passorder for each layer indicates the use of the “American” weldingtechnique, where L indicates right-to-left and R indicates left-to-right. The grain orientations predicted for these two solutions arecompared with reference grain orientation measurements, madeusing image processing software used in previous studies [10,11].

4. Comparison between grain orientation simulationsand measurements and discussion

In this section the grain orientations calculated by modellingare compared to reference measurements made by EDF usingoptical measurements on macrographs. The scale used for thisanalysis is 2 � 2 mm, since it has previously been shown thatthis allows a good compromise to be found between accurateultrasound modelling and data volume, when the conventionalfrequencies of 1 or 2 MHz are used for the ultrasonic testing. Thewavelength corresponds to a few millimeters, whereas the grainsize is approximately 200 mm [9]. The chamfer widths used in themodel were 40 mm at the upper part of the weld, and 4 mm at thebottom, with an overall height of 24 mm. The final grain orienta-tion matrices have dimension of 40 � 20 mm, as the weld isplanned (see Fig. 1). The grain orientations varied from 0 to 180�

(90� ¼ vertical orientation). MINA resulting grain orientationmatrix is calculated with the same 2 � 2 mm scale. This procedureenables to have the same matrix dimensions for the comparison.The difference matrix between the reference measurements andthe modelling results is simply the difference of the two corre-sponding matrices. When the modelling value corresponds to thereference value the difference is zero. Large differences could belocally observed (30� or more). This difference matrix is convertedas a map of differences in Fig. 2. The use of level lines and greycolour scale enable a global analysis of MINA modelling results.These maps make easier various parametric studies.

Several conclusions can be drawn from these figures. Firstly, themean error (Dq) and the standard deviation (sq) between thereference and model values lie globally in the same domain, i.e.between 15� and 17� for the mean value, and approximately 10�

and 12� for the standard deviation. In a previous study of moreacademic welds, the value for Dq mean ranged between approxi-mately 10� and 13� [10]. As this weld is more complex, and due tothe slight slope of the layers, these values reflect more variationsbetween modelling and macrograph measurements than in theprevious study. The final error maps show that the MINA model isnot excessively sensitive to this slight slope, despite the fact that itis not reproduced in the modelled approach.

Secondly, the error maps ((a) and (b)) demonstrate that thewelding pass order recorded in the notebook leads to the bestsolution, even though the alternative solution (Solution 2) is notvery different from Solution 1. The grain orientation differencebetween Solutions 1 and 2 has an average value of 8�. Local grainorientation differences could be expected to produce some modi-fications to the predicted ultrasound beam behaviour.

Thirdly, in order to degrade the results, substantially incorrectnotebook recordings are needed. For example, Solution 3 used inFig. 4 (d) is composed of 8 layers (number of passes per layer: 1, 2, 2,3, 3, 3, 4, 4), using a left-to-right pass order. This confirms that theMINA model is robust.

Fourthly, our comparison with the analytical solution given byOgilvy’s model, adapted to the CANDE weld, shows that the MINA

Fig. 4. Contour plots of grain orientation differences.

J. Ye et al. / International Journal of Pressure Vessels and Piping 93-94 (2012) 17e2120

model is closer to the reference solution even though the asym-metrical behaviour was taken into account in the analytical solu-tion [14]. In the case of the CANDEweld, the difference between thetwo models is smaller when the mean value is considered. Never-theless, due to a large area towards the left side of the weld inwhich there is a change in the resulting orientations, differences inultrasound propagation could be expected. It is also interesting tonote that the buttering has little effect on grain growth, as there areno strong differences near to this zone. It was observed that thegrains in the buttering zone are quite perpendicular to the chamfer,and this observation is in agreement with the assumptions made inthe MINA code [4].

Fifthly, the errors are always localised in the same area (left andupper left zones), which is most probably a consequence of themodification to the welding process during the 18th pass as theorder of passes is changed: from right-to-left it changes to left-to-right. This 18th pass probably remelted at the outside edge of thelayer, producing an unusually large deposit. Such a variation in thedeposits made during passes should be avoided, to avoid anychange to the symmetry of the process, which would havea noticeable effect on grain orientations. No model is able to takeinto account such phenomena at this moment. It confirms the needof a careful record of the welding procedure by the welder fora better understanding of the weld properties. For the sole ultra-sonic point of view it is known that if a large area is characterisedby a difference in mean grain orientation, the beam path is modi-fied [11].

5. Conclusions

In this paper, we focus on the grain orientation description ofa bimetallic austenitic stainless steel weld. The MINA code was

used to simulate the grain orientation of a multi-pass weld, andfor the analysis of a macrograph of the weld.

We show that even a macrograph may be read in two differentways; overall, the grain orientation could be correctly predictedwith a better accuracy than an analytical solution. Nevertheless, it isalso clear that the correct pass order is highly crucial to graingrowth, such that, together with a correct description of thenumber of passes in a layer, it is the most important parameter indescribing a weld.

A generic solution would be to use the advanced modelling tool(MINA) in an inverse process, to reconstruct unknown parameters.Good results were obtained by C. Gueudré et al. with remeltingparameters [13]. The latter study demonstrated that the mostcrucial point is that of reconstructing the pass order using theinverse technique, whenever the welding notebook is unreliable.However, it should be pointed out that, from the mathematicalpoint of view, the inverse problem is more complex [15]. The passsequence also influences residual stresses [16,17]. It would be ofgreat interest to combine these two research fields to propose thebest sequence order: improving ultrasonic investigation andreducing residual stresses.

The MINA code has been dedicated to shielded metal arcwelding and flat welding. Some preliminary works have been doneto enlarge the applications to TIG welding and welding in position[12]. This would be developed in the framework of a Frenchcollaborative research programs called MOSAICS at the beginningof 2012.

More recently, ultrasonic phased array testing has beenincreasingly adopted for the inspection of dissimilar metal welds,since this technique can improve the probability of detections(PODs), and has an improved sensitivity to defects located inattenuating media and specimens with complex curvatures. Inthe case of phased array transducers, the delay laws could be

J. Ye et al. / International Journal of Pressure Vessels and Piping 93-94 (2012) 17e21 21

incorrectly calculated with incorrect material descriptions [14]. Theadvantage of the MINA model is confirmed when it is vital toachieve more realistic grain orientation predictions.

Acknowledgements

We gratefully acknowledge the support provided by the LCND,and CANDE, and SKKU. The authors also wish to thank EDF R&D inMoret sur Loing (France) for granting them with permission to usethe MINA code for this study, and thank KINS for its support withDMW research.

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