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SciVerse ScienceDirect

Procedía Engineering 15 (2011) 3 870 - 3874

Procedía Engineering

www.elsevier.com/Iocate/procedia

Advanced in Control Engineering and Information Science

The Numerical Analysis of Heterogenic Welding Joint

residual stresses

Shu Xua a*

aSchool of Mechanical Engineering, Huaihai Institute of Technology, Lianyungang , China

Abstract: Using the finite element software, a sequential coupling finite element procedure is developed to calculate the welding residual stress in the welding joint of 0Cr18Ni9/45, 1Cr9Mo/45 and 1Cr9Mo/0Cr18Ni9. It is shown that the peak axial stresses and hoop stresses are shown in the side of HAZ of 45 for both 0Cr18Ni9/45 and 1Cr9Mo/45and the minimum stress is shown in the side of 0Cr18Ni9 no matter the A302 or Incone182 is used. It is concluded that replacement of A302 by Incone182 can decrease the residual stress and promote the resistance of stress corrosion cracking, which provides a reference for the material change and welding of piping.

© 2011 Published by Elsevier Ltd. Selection and/or peer-review under responsibility of [CEIS 2011]

Keywords; residual stress, numerical analysis, heterogenic welding joint

1 Introduction

The thermal stress of heterogeneous welding joints with temperature changes have been analyzed already in past. The intensity and plastic toughness of joint in normal temperature and high temperature have been evaluated by the mechanics performance test, and some important rules are found. The welding residual stress of welding joint is one of the important factors that cause the early failure of heterogeneous steel[1-3]. Because differences of weld filler metal in the heterogenic joint, welding heat affected zone

* Corresponding author. Tel.:+015298605182; E-mail address: gladxushu@163.com.

1877-7058 © 2011 Published by Elsevier Ltd. doi:10.1016/j.proeng.2011.08.724

and chemical composition, organization structure, mechanical properties and thermal physical properties in the base materials[4-6].This leads joints in complex stress state during the welding process. In addition, the heterogeneous steel welding process does not have post-welding heat treatment at spot commonly, so larger welded joint residual stress will be produced on the joint after it is welded. Welding joint residual stress is added with working load stress will lead to joint parts stay in a high stress level. When joints are served under corrosive environment (such as wet H2S environment), severe stress corrosion cracking will be happened easily. Therefore, study and analysis on the welded joint residual stress has important significance to guarantee the reliability of the steel welding joint. And carbon migration phenomenon is considered to be another important factor affected the service life of heterogeneous welding joints. Extensive literature illustrate that austenitic electrodes will lead failure when they are serviced in high temperature normally in engineering, but nickel-based electrode welding joints can effectively reduce the residual stress and can restrain the carbon migration, the service life of joint is improved. In recent years, nickel-based electrode are more and more used for heterogeneous steel welding in engineering to improve the high temperature performance of the heterogeneous steel welding joint.

In this paper, numerical simulation of welding residual stress analysis about the welded joint of heterogeneous steel (45 steel, 1Cr9Mo and 0Cr18Ni9 heterogeneous steel joint is performed by using ABAQUS finite element software, which is welded by austenitic A302 electrode and nickel based Inconel182 electrode) used in piping systems of petrochemical plant.

2. The finite element models of heterogenic joint

Using ABAQUS6.5, a followed coupled the thermal stress calculation program to simulate the welding residual stress is studied. Firstly, the thermal analysis in calculating is made, calculation results files of each node temperature field will be as mechanics analysis of predefined field, in the process of mechanics analysis, each point of temperature from the predefined games is read, and interpolation is calculated , the same unit and the node is adopted in thermal analysis and force analysis .

Figure 1 are the model of pipeline welds weld joint geometry, structure and size of weld groove are shown in the figure. Base materials are 1Cr9Mo, 0Cr18Ni9 and 45 steel. Weld material is A302 or Incone182, those connectors are: 1Cr9Mo+A302+45, and1Cr9Mo+Incone182+45, and OCrl 8M9+A302+45, and 0Crl8Ni9+Inconel 82+45.

\ iKUtlLI Material 1 \ / / Material 2 n

Fig 1 Geometric model of the welding joint

Fig. 2 Meshing of the welding joint

According to the requirements of GB985-88 "Basic forms and sizes of weld grooves of the gas welding, arc welding and gas metal arc welding "to using v-groove. Weld is completed through four-pass welding. In order to prevent grain growth and carbide precipitation of heat-affected zone ,layer temperature should be controlled below the 150 °C .Preheating and heat treatment after welding are not done.

In order to facilitate the calculation, simplified model to reduce calculation has a pivotal role, the assumptions is made:

1. Do not consider heat transfer between the work piece and test desk;

2. Ignore chemical reaction and stirring, convection phenomenon in the welding pool. Because the pipe is belonged to ax-symmetric model, ax-symmetric unit is adopted in model. Considering the accurate description of greater temperature gradient, weld and heat affected zone need to be meshed densely, so not only results are getting better, but also the computational time is reduced. Weld and heat affected zone meshing are shown in figure 2

Firstly, temperature field analysis is calculated, the calculation results of each node temperature field is outputted to results files as force analysis of predefined field. Temperature of each node from predefined field is read by process, and interpolation calculation in force analysis is made. The same unit and node is used in thermal analysis and force analysis. There are 2244 nodes and 4598 units in total. Unit types are ax-symmetric units, the temperature field calculating unit types are DCAX4 and stress field calculating unit types are CAX4.

3. Analysis of the finite element model

Using A302 and Incole182 weld 1Cr9Mo/45 of dissimilar steel welding joint, simulation calculated welding residual stress distribution are shown in Figure 3~4.

E, S22 (JiJ

t:.i«etcs

ti.SHietCS

i-tUascHR

-l.lbSi+CS

(a) axial stress (b) hoop stress

Fig. 3 Residual stress distribution of welding joint lCr9Mo(left)+A302+45(right)

-♦Z.iKiKE

- ♦Z.liietC:

- ♦l.S^etC: -K.iHtNJJ --S.MKttUfc ►-7. «Will --l.HiiitL:

--i.lfliitta

(a) axial stress (b) hoop stress

Fig. 4 Residual stress distribution of welding joint 1CR9Mo(left)+Inconel182+45(right)

From the results, the maximum stress is existed in the pipe wall; residual stress in pipe wall thickness direction is relatively small, so analysis and discussions axial and hoop welding residual stress on the outer wall of pipe are made in this article.

We can see that: distribution of welding residual stress in welded joints is more similar, but stress level is different. In the heat affected zone, axial stress is greater tensile stress; but is compressive stress in the weld area; stress is gradually decayed away from the weld. Hoop stress is larger relative to the axial stresses, and is greater tensile stress in the weld seam and heat-affected zone, stress of heat-affected zone is slightly larger than that of the weld, the stress away from heat affected zone is gradually decayed, and becomes compressive stress.

From figure 5, 6 and 7 comparative analysis of simulation results we can see that no matter the electrode is A302 or Inconel182, maximum axial tensile stress of 0Cr18Ni9/45 and 1Cr9Mo/45 is occurred in 45 steel side, and stress in 1Cr9Mo side are much smaller than that in 0Cr18Ni9 side, and amplitude is reached 50%; Maximum axial tensile stress in 1Cr9Mo/0Cr18Ni9 joint is appeared in 1Cr9Mo steel side. There is a large difference between thermal expansion coefficient of 45 steel and thermal expansion coefficient of 0Cr18Ni9, And there is also a large difference between thermal expansion coefficient of 45 steel and thermal expansion coefficient of welding material, Unmatched hot expansion coefficient, the expansion and contraction on constraints of 45 steel leads the larger residual stress in 45 steel side; and because of weld material expansion coefficient covers the 0Cr18Ni9 and 45

steel of hot expansion coefficient gap ,the stress level of 0Cr18Ni9 side is much smaller than stress of lCr9Mo side.

350 ■ 300 ■ 250 ■ 200 ■ 150100 ■

-.-A302 \ Income 182

lCrl 81TÍ 9Ti Will 45

20 40 150 80

Distance akngthfi outside ài (a) axial residual stress

20 40 60 8 0

Distaruce alcmgthjé outside A&m

(b) hoop residual stress Fig. 5 Residual stress of dissimilar welding of 0Crl8Ni9(left) and 45(right)

20 40 60 80

Distaras ¿Long the outside Aum (a) axial residual stress

(b) hoop residual stress Fig.6 Residual stress of dissimilar welding lCr9Mo(left) and 45(right)

O 20 40 60 BO lOO O 20 40 SO SO 100

Distance along the outside /mm Distance along the outside /mm

(a) axial residual stress (b) hoop residual stress

Fig 7. Residual stress of dissimilar welding 1Cr9Mo and 0Cr18Ni9

4. Conclusion

This chapter use large commercial finite element software ABAQUS on six kinds of dissimilar steel welding joint for finite element simulation analysis and reached a distribution of residual stress.

1. Distribution of six welding residual stress of welded joint are more similar, but stress levels vary. In the heat affected zone the axial stress is the larger tensile stress; compressive stress is in the weld area; stress is gradually decayed away from the weld. Hoop stress is larger than axial stress. Greater tensile stress is in the weld seam and heat-affected zone .The stress away from heat affected zone is gradually decayed.

2. Regardless of using austenitic electrodes A302 or Inconel182 of NI electrode, maximum welding residual stress is produced in 45 heats affected zone of steel in welded joints of 1Cr9Mo/45 steel and stress levels are minimal in 0Cr18Ni9 side, Stress on the 1Cr9Mo side following behind. Residual stress is usually existed in 1Cr9Mo side for 0Cr18Ni9/1Cr9Mo Welding.

3. Residual stress can be effectively reduce by using Inconel182 NI electrode instead of austenitic welding electrodes A302.Residual axis stress in the side of 45 steel is reduced near 20%, hoop residual stress is reduced as much as 25%, which can enhance the capacity of resistance to stress corrosion cracking. This provides a scientific basis for selection of welding method for pipe material replacement process.

Reference

[1] Cao.Z, Dong.P, Brust,F. Fast thermal solution procedure for analyzing 3D multi-pass welded structures[J]. Welding Research Council Bulletin, 2000, 55(455): 12~21

[2] Dong,P. Residual stress analysis of a multi-pass girth weld: 3-D special shell versus axisymmetric mdodels[J]. Journal of pressure vessel technology. ASME, 2001, 5(123): 207~213

[3] E. F. Rybicki, R. B. Stonesifer, Computation of residual stresses due to multipass welds in piping systems[J]. Trans ASME Journal of Pressure Vessel Technology, 1979, 101: 149~154

[4] P. Dong, F. W. Brust, Welding residual stresses and effects on fracture in pressure vessel and piping components: A Millennium Review and Beyond [J]. Trans. ASME Journal of Pressure Vessel Technology, 2000, 122: 329~338

[5] Daniel Rosenthal, Mathematical theory of heat distributation during welding and cutting[J]. Welding Research Supplement, 1941, 5: 220~234

[6] Randy C. John, Arthur D. Pelton, Arthur L. Young, William T. Thompson, Ian G. Wright, Theodore M. Besmann[J]. Assessing Corrosion in Oil Refining and Petrochemical Processing, 2004, 7(1): 163~173