E-Journal of Advanced Maintenance Vol. 13 No. 1 (2021) 12-20
Japan Society of Maintenology

A Novel Simulation Method of Thermal Cycle in Multi-pass Welding
Process by Temper Bead Technique
Lina YU1,*, Kazuyoshi SAIDA1, Masahito MOCHIZUKI1, Kazutoshi NISHIMOTO4 andNaoki CHIGUSA2
1Osaka University, 2-1 Yamadaoka, Suita, Osaka 565-0871, JapanThe Kansai Electric Power Co., Inc., 8 Yokota, 13 Goichi, Mihama-cho, Mikata-gun, Fukui
919-1141, Japan
2

ABSTRACT
Temper bead welding technique has been developed as one of effective repair method for pressurized water
reactor, in case that post weld heat treatment (PWHT) is difficult to carry out. It is essential to confirm thetempering effect on the mechanical properties, and the appropriate welding conditions in temper bead welding
needs to be predicted before the actual welding. Therefore, in this study, a novel numerical simulation method
was proposed for predicting the temperature distribution and thermal cycle during multi-pass welding processby temper bead technique. As the results, the temperature distribution, such as Ac1 line and weld metal line,
were in good agreement between simulated and experimental results. Furthermore, based on the simulated
thermal cycles the hardness distribution in heat affected zone (HAZ) was calculated, and the calculated hardness
was in good accordance with the experimentally measured result. It follows that the currently proposed
simulation method is effective for estimating the tempering effect during temper bead welding prior to actual
welding.
KEYWORDS
Temper bead welding, Simulation model, FEM, Temperature distribution,
Hardness

Article history:
Received October 2020
Accepted May 2021

ARTICLE INFORMATION

1.

Introduction

Low alloy steel ASTM A533B possessing the superior low-temperature toughness and weldability
is widely used to build pressurized water reactor vessels in nuclear power plants. However, theexcellent mechanical properties of the base metal will be altered by the thermal cycles imposed bywelding processes, and the increase in hardness and the loss of toughness always occur in the heataffected zone of the welds [1]. Therefore, post weld heat treatment (PWHT) is normally required torecover the toughness, eliminate the residual stress and reduce the hardness. However, PWHT issometimes difficult to perform in operation in the case of repairing for large-scale structures. In
practice, the temper bead welding technique is an effective repair welding method instead of PWHT
[1-3]. Temper bead welding is a kind of multi-pass welding, in which the tempering effect is causedby heat-arising from the subsequent multi-layer weld thermal cycles. And it is essential to confirm thetempering effect on the mechanical properties and the appropriate welding conditions needs to bepredicted prior to the actual welding.
To achieve the required tempering effect during temper bead welding, it is very important to predictthe proper thermal cycle in multi-pass welding. Therefore, it is desired to develop a simple and useful
numerical simulation method with the help of computer. Using the traditional simulation method [4-6],
in order to prepare the simulation model, it is necessary to get the detailed information of the welding
cross section after the actual welding. Therefore, the simulation model is difficult to complete prior to
the actual multi-pass welding, and it takes a lot of time to create the complicated multi-pass welding
model, especially difficult for the case for more than 100 pass welding. Therefore, a simple and quick
simulation method without the detailed information of the welding cross section after the actual
welding is expected to establish prior to the actual welding. In this study, a novel simply numericalsimulation method was proposed for predicting the temperature distribution and thermal cycle duringmulti-pass welding process by temper bead technique, based on the single-pass bead shape database.
* Corresponding author, E-mail: yulina@mapse.osaka-u.ac.jp
ISSN-1883-9894/10 © 2010 – JSM and the authors. All rights reserved.

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L Yu, et al./ A Novel Simulation Method of Thermal Cyclein Multi-pass Welding Process by Temper Bead Technique

And the simulated temperature distribution was compared with the experimental result to confirm theeffectivity of the proposed simulation method. Furthermore, based on the simulated thermal cycles thehardness distribution in heat affected zone was predicted, which was also compared with theexperimentally measured hardness to verify the effectivity of the newly proposed simulation method.

2. Materials and experimental procedures
The chemical compositions of the base metal low-alloy steel A533B and filler material MG-S56X
used were shown in Table 1. The chemical compositions of the filler material MG-S56X were similar
to the base metal A533B.
The single-pass welded sample (100×35×150 mm, shown in Fig. 1) was produced by GTAW (Gas
Tungsten Arc Welding) with the welding conditions shown in Table 2. As shown in Fig. 2, the 7 layer- 152 pass temper bead welding was performed using the consistent layer technique [7], with thewelding conditions shown in Table 3. The section surface was cut from the single-pass welded sample,
and the sectioned surfaces of 1-layer, 3-layer and 7-layer weldments were cut from the multi-passwelded sample. The Vickers hardness was measured in the cross sectional area of the specimens after
polishing and etching with 3% nital solution. The Vickers hardness measurement was performed at aload of 9.8N for 20s. In order to simulate the actual repair welding, the thermal cycle in heat affectedzone (HAZ) of the 7 layer-152 pass welded sample was calculated using the following finite element(FE) simulation method proposed.
Table 1 Chemical compositions of materials
Chemical compositions (mass %)Material
A533B(Base metal)

MG-S56X(Filler metal)

C

Si

Mn

P

S

Ni

Cu

Cr

Mo

Ti

Al

Fe

Co

0.12

0.26

1.43

0.006

0.002

0.53

0.02

0.01

0.51

-

0.038

Bal.

-

0.06

0.43

1.51

0.006

0.005

0.89

0.03

0.04

0.35

0.09

0.01

Bal.

<0.01

Fig. 1 Specimen for single-pass and multi-pass welding
Table 2 Welding conditions of single-pass welding
Welding
condition

Current[A]

Voltage[V]

Wiresending[cm/min]

Welding
speed[cm/min]

Heat
input
[J/cm]

①

250

16.7

200

10

25050

②

120

13.2

90

30

3168

③

200

15.2

160

30

6080

④

100

11.2

80

10

6720

⑤

200

15.7

150

20

9420

⑥

250

16.7

220

20

12525

⑦

140

13.2

110

30

3696

⑧

180

14.7

130

30

5292

13

L Yu, et al./ A Novel Simulation Method of Thermal Cyclein Multi-pass Welding Process by Temper Bead TechniqueFig. 2 Schematic illustration of temper bead welding
Table 3 Welding conditions of temper bead welding (7 layer-152 pass welding)Current Voltage
Wire feeding
Welding speed Heat input
Number
Layer
[A]
[V]
speed [cm/min][cm/min][J/cm]of passes
250
16.7
200
10
25050
1st
12
2nd

120

13.2

90

30

3168

39

3rd

140

13.2

110

30

3696

30

4th

200

15.2

160

30

6080

23

5th

200

15.7

150

20

9420

16

6th

200

15.7

150

20

9420

16

7th

200

15.7

150

20

9420

16

3. Novel simulation method for multi-pass welding
3.1 Bead shape database of single-pass welding
The single-pass welded sample was produced by GTAW with the welding conditions shown in
Table 2. The section interface was cut from the center of the single-pass welded sample, and the crosssections of the single-pass welded sample were shown in Fig. 3. From the actual single-pass weldedcross section, the information of bead width, height and depth for each single-pass welding condition
has been collected as the database of weld bead shape and size for the novel FE simulation.

Fig. 3 Cross-sections of single-pass welded sample with different welding conditions

3.2 Concept of new simulation method
In the traditional simulation method, for example the simulation model as shown in Fig. 4, in orderto prepare the simulation model, it was necessary to get the detailed information by taking the actual
photographs of the welded cross-section of each layer after the actual welding. Therefore, thesimulation model was difficult to complete prior to the actual multi-pass welding, and it took a lot oftime to create the complicated multi-pass welding model, especially difficult for the multi-passwelded sample more than 100 pass welding as shown in Table 3. Therefore, a simple and quick
simulation method without the detailed information of the welding cross section after the actual14

L Yu, et al./ A Novel Simulation Method of Thermal Cyclein Multi-pass Welding Process by Temper Bead Techniquewelding is expected to develop prior to the actual welding.

Fig. 4 Traditional simulation model for multi-pass welding

In this study, a novel simply simulation method was proposed, for predicting the temperature
distribution and thermal cycle during multi-pass welding process by temper bead technique based on
the obtained single-pass bead shape database, as shown in Fig. 5. According to the observed
single-pass weld bead shape database, the heating range of each welding bead was automaticallyselected. The bead shape is consisted with two ellipses (up and down), and the element range fit theEquations (1) and (2) will be automatically selected as the heating part of the weld bead.

Y2 Z2
 2 1
aup2
bup

（1）

Y2
Z2
 2 1
2
a downbdown（2）Where, Y/Z is the central coordinate of each weld bead, aup is the half width of bead, bup is the heightof bead, adown is the half width of bead, and bdown is the depth of bead.
Since the element range of each bead can be automatically selected, it is not necessary to create thematerial properties of each bead on creating the analysis model. And using this simulation method, theremelting between passes and the remelting between layers can be automatically considered in thesimulation model, which is more close to the actual multi-pass welding. Furthermore, the model iseasy to prepare, which can reduce the time for the simulation model creation, and the actual
cross-sectional photographs of the sample are not needed, indicating that the simulation model can beprepared prior to the actual multi-pass welding.

Fig. 5 Concept of the novel simulation method

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L Yu, et al./ A Novel Simulation Method of Thermal Cyclein Multi-pass Welding Process by Temper Bead Technique

4. FE simulation of temper bead welding and discussion
4.1 FE simulation model of temper bead welding
According to the novel proposed simulation method, the simulation model was also changed asshown in Fig. 6. There is only weld metal (WM) zone and base metal (BM) in the model. In order toselect the bead shape more similar to the actual bead, the distance between the meshes of the WM partwas set as 0.2 mm, which was finer than that of BM. And the distance between the meshes of the BM
near WM was set to 0.5 mm, to easily analysis the thermal cycle in HAZ. As shown in the magnified
part of Fig. 6, the heating range of each welding pass was automatically selected, based on theobtained single-pass bead shape database, according to the different welding conditions of every
layer.
The temperature dependencies of physical properties of A533B are illustrated in Table 4. The
welding conditions were the same as the experimental conditions shown in Table 3, which followed
the consistent layer technique in temper bead welding.

Fig. 6 Simulation model for 7 layer - 152 pass welding
Table 4 Temperature dependencies of material properties of A533B steel

20

445

0.039

478

210

Possion’s
ratio
(－)
0.3

200

517

0.0389

455

202

0.3

12.7e-6

400

592

0.036

405

188

0.3

13.9e-6600

723

0.0317

238

160

0.3

13.8e-6

Temperature(℃)

Specificheat(J/kg℃)

Thermalconductivity(W/mm℃)

Yield
Strength(MPa)

Young’smodulus(GPa)

Thermalexpansion(1/℃)
12.0e-6800812

0.0378

75

115

0.3

12.6e-61000

6580.0309

17

93

0.3

12.6e-6

1300

721

0.03655

100.3

14.5e-6

4.2 Temperature analysis of temper bead welding by FEM simulation
The temperature distributions produced by multi-pass thermal cycles in welds during temper beadwelding were calculated using the novel proposed simulation method of the three-dimensional finite
element analysis code, developed specifically for multi-pass welding simulation. Fig. 7 presents thecalculated peak temperature distribution in the middle cross-section of 7 layer - 152 pass welds. The
different peak temperatures are indicated by the different colors. The WM part was selected based on
the previously obtained database of the single-pass bead shape, and WM range with peak temperature
higher than the melting point of 1500 ℃ is shown in red color. And the region of HAZ are shown inrainbow colors according to the different peak temperatures.

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L Yu, et al./ A Novel Simulation Method of Thermal Cyclein Multi-pass Welding Process by Temper Bead TechniqueFig. 7 Peak temperature distribution of 7 layer-152 pass welding

The region of the simulated WM with the maximum temperature higher than the melting point at
the cross section was compared with the experimental result, as shown in Fig. 8. The height of WM
region from the surface of the base metal were almost the same to the experimental result. And the Ac1line comparison between the simulated result and the experimental result was shown in Fig. 9. As theresult of calculation, the deepest point of the Ac1 line on the left side of multi-pass welding was 4.6
mm far from the sample surface, same to the actual welded cross sections, and the depth of the rightside was 4.2 mm in both calculated result and experimental result. These facts indicated that thesimulated temperature distribution agreed well with the experimental result.

Fig. 8 Fusion line comparison of simulated result and the experimental result of 7 layer - 152 pass welding

Fig. 9 Ac1 line comparison of simulated result and the experimental result of 7 layer - 152 pass welding17

L Yu, et al./ A Novel Simulation Method of Thermal Cyclein Multi-pass Welding Process by Temper Bead Technique

4.3 Hardness prediction based on the simulated thermal cycles
Neural network (NN) [8,9] is a mathematical model or computational model that simulates the
structure and/or functional aspects of biological neural networks. The NN-based hardness prediction
system has been constructed previously based on the experimentally obtained hardness database by
the authors [5]. According the thermal history at every grid node in HAZ, the simulated thermal cycle
parameters (for example, Tp, CR) were fed into the proposed hardness prediction system, and thehardness at every grid node was calculated.
According the calculated hardness of every grid node, the visual hardness distribution in the HAZ
after 1-layer welding, 3-layer welding and 7-layer welding were shown as color chart maps in Fig. 10
using the Mathematica software. Besides the red WM and grey BM regions, the hardness in the HAZ
is shown with rainbow colors according to the different hardness levels. It could be found that after
1-layer welding as shown in Fig. 9 (a), there were some hardened zone with hardness higher than 350
HV appeared in the CGHAZ adjacent to the WM. However, after 3-layer and 7-layer temper beadwelding as illustrated in Fig. 9 (b) and (c), the hardness in the whole HAZ was decreased and allvalues were lower than 350HV (the required specification in industry).

(a) 1 layer-12 pass welding(b) 3 layer-81 pass welding(c) 7 layer-152 pass welding
Fig. 10 Calculated hardness distribution of 7 layer-152 pass welding

The predicted hardness was compared with the experimentally measured results for the HAZ of
A533B low-alloy steel after 7 layer - 152 pass welding, as shown in Fig. 11. The predicted and18

L Yu, et al./ A Novel Simulation Method of Thermal Cyclein Multi-pass Welding Process by Temper Bead Techniquemeasured values were performed along the yellow dotted line 2.5 mm far from the surface of the basemetal, and the measurement distance of hardness was 1 mm. The red points were the experimentallymeasured hardness, and the blues points were the calculated hardness using the neural network-based
hardness prediction system, based on the FE simulated thermal cycle. The predicted hardness was ingood accordance with the experimentally measured hardness, and both the predicted and the measured
hardness were lower than 350HV (the required specification in industry) after 3-layer and 7-layer
temper bead welding. It follows that the proposed simple simulated method for multi-pass welding isuseful and effective for estimating the tempering effect in temper bead welding.
It can be concluded that using the proposed simple simulation method, the hardness in HAZ is
successfully predicted prior to the actual temper bead welding based on the FE simulated thermal
cycle. If the calculated hardness in HAZ is higher than 350HV (it means it cannot fit the required
specification in industry), the welding conditions would be modified. Thus, the appropriate welding
conditions can be selected prior to the actual welding. The present novel simulation method is greatly
useful and effective for the repair welding for the large structures.

(a)1 layer-12 pass welding(b) 3 layer-81 pass welding(c) 7 layer-152 pass welding
Fig. 11 Comparison of calculated hardness and measured hardness

5. Conclusions(1) In order to simplify the FEM thermal cycle analysis, a novel numerical simulation method was
proposed for predicting the temperature distribution and thermal cycle of temper bead welding,19

L Yu, et al./ A Novel Simulation Method of Thermal Cyclein Multi-pass Welding Process by Temper Bead Techniquebased on the obtained bead shape database.
(2) The thermal history in HAZ of 7 layer - 152 pass welding by the consistent layer temper beadtechnique was simulated using the proposed method. As the results, the temperature distribution,such as Ac1 line and weld metal line, was in good agreement between simulated and experimental
results.
(3) Based on the simulated thermal cycle, the hardness distribution in HAZ was predicted, and thecalculated hardness was in good accordance with the experimentally measured result. It followedthat the proposed simulation method was greatly useful and effective for estimating the tempering
effect during temper bead welding prior to actual welding.

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