Residual Stresses in Weld Repairs and Mitigation by Design · RESIDUAL STRESSES IN. WELD REPAIRS...

See discussions, stats, and author profiles for this publication at: https://www.researchgate.net/publication/269277560

Residual Stresses in Weld Repairs and Mitigation by Design

Conference Paper · June 2014

CITATIONS

2

READS

197

1 author:

Some of the authors of this publication are also working on these related projects:

Residual Stress Profile Estimation Scheme View project

Shaopin Song

University of Michigan

21 PUBLICATIONS 153 CITATIONS

SEE PROFILE

All content following this page was uploaded by Shaopin Song on 09 December 2014.

The user has requested enhancement of the downloaded file.

https://www.researchgate.net/publication/269277560_Residual_Stresses_in_Weld_Repairs_and_Mitigation_by_Design?enrichId=rgreq-8477312830856b9cd91ea44433326fd8-XXX&enrichSource=Y292ZXJQYWdlOzI2OTI3NzU2MDtBUzoxNzI1MTc4Mzg4Mjc1MjZAMTQxODE0Mjg2NjYzMw%3D%3D&el=1_x_2&_esc=publicationCoverPdf

https://www.researchgate.net/publication/269277560_Residual_Stresses_in_Weld_Repairs_and_Mitigation_by_Design?enrichId=rgreq-8477312830856b9cd91ea44433326fd8-XXX&enrichSource=Y292ZXJQYWdlOzI2OTI3NzU2MDtBUzoxNzI1MTc4Mzg4Mjc1MjZAMTQxODE0Mjg2NjYzMw%3D%3D&el=1_x_3&_esc=publicationCoverPdf

https://www.researchgate.net/project/Residual-Stress-Profile-Estimation-Scheme?enrichId=rgreq-8477312830856b9cd91ea44433326fd8-XXX&enrichSource=Y292ZXJQYWdlOzI2OTI3NzU2MDtBUzoxNzI1MTc4Mzg4Mjc1MjZAMTQxODE0Mjg2NjYzMw%3D%3D&el=1_x_9&_esc=publicationCoverPdf

https://www.researchgate.net/?enrichId=rgreq-8477312830856b9cd91ea44433326fd8-XXX&enrichSource=Y292ZXJQYWdlOzI2OTI3NzU2MDtBUzoxNzI1MTc4Mzg4Mjc1MjZAMTQxODE0Mjg2NjYzMw%3D%3D&el=1_x_1&_esc=publicationCoverPdf

https://www.researchgate.net/profile/Shaopin_Song?enrichId=rgreq-8477312830856b9cd91ea44433326fd8-XXX&enrichSource=Y292ZXJQYWdlOzI2OTI3NzU2MDtBUzoxNzI1MTc4Mzg4Mjc1MjZAMTQxODE0Mjg2NjYzMw%3D%3D&el=1_x_4&_esc=publicationCoverPdf


https://www.researchgate.net/institution/University_of_Michigan?enrichId=rgreq-8477312830856b9cd91ea44433326fd8-XXX&enrichSource=Y292ZXJQYWdlOzI2OTI3NzU2MDtBUzoxNzI1MTc4Mzg4Mjc1MjZAMTQxODE0Mjg2NjYzMw%3D%3D&el=1_x_6&_esc=publicationCoverPdf



1 Copyright © 2014 by ASME

Proceedings of the ASME 2014 33rd International Conference on Ocean, Offshore and Arctic Engineering OMAE2014

June 8-13, 2014, San Francisco, California, USA

OMAE2014-24547

RESIDUAL STRESSES IN WELD REPAIRS AND MITIGATION BY DESIGN

Shaopin Song and Pingsha Dong1

Welded Structures Laboratory Department of Naval Architecture and Marine Engineering

University of Michigan, Ann Arbor, MI 48109

ABSTRACT1

It is well known that residual stresses caused by weld repairs

tend can be significantly higher than those caused by initial

fabrication welds due to severe restraint conditions associated

with typical weld repairs. This paper presents an in-depth

investigation of repair weld geometry effects on residual stress

distribution characteristics, particularly in terms of the through-

thickness membrane and bending content that can be shown

fundamentally different from that in initial fabrication welds.

The results indicate that repair weld design parameters in terms

of repair length, depth, and width are of critical importance to

the mitigation of residual stresses. A 3D finite element residual

stress modeling procedure developed and validated for

numerous case studies in the past, after further validation on a

selected component in the current study, is used throughout this

investigation.

Keywords: Residual stresses, weld repair, fitness for service,

fracture assessment, membrane and bending decomposition,

finite element modeling, mitigation techniques

NOMENCLATURE AND ABBREVIATION r radius of the pipe, mm

t pipe thickness, mm

σ(x) residual stress, MPa

σm membrane component of residual stress, MPa

σb bending component of residual stress , MPa

σs.e. self-equilibrating component, MPa

DH deep-hole

FE finite element

FFS fitness-for-service

HAZ heat affected zone

ND neutron diffraction

ID inner diameter

OD outer diameter

1 Professor and corresponding author [email protected]

WCL weld centerline (through-thickness)

WT weld toe (through-thickness)

1. INTRODUCTION Weld repairs have been increasingly used for life extension for

pressure equipment and aging infrastructures. There is a

growing interest in a better understanding of repair weld

residual stress effects on structural integrity as a result of some

recent incidents, such as one incident involving a crack initiated

by localized damage at girth weld repair [1] in nuclear power

plant piping system in Europe and stress corrosion cracking at a

repair weld at a US nuclear power plant. [2]. A subsequent

industry survey has unearthed that over 40% of weld repairs

resulted subsequent cracking [3].

As discussed in a number of recent publications [7-15], the

main difference in residual stresses between weld repairs and

initial fabrication welds is that a repair weld is typically

subjected to multiaxial stress state due to severe restraints in

both longitudinal and transverse directions, while in initial

welds typically experiences severe restraints only in its

longitudinal direction. As a result, both through-thickness

membrane and bending content in residual stress distributions

tend to be significantly elevated. Such findings are corroborated

by experimental evidences reported by Bouchard et al [8] and

Elcoate et al [12]. These past investigations [7-12] have

resulted in some important findings residual stresses associated

with weld repairs:

(1) Residual stress fields at repair welds tends to exhibit a

strong 3-D distribution feature, dependent upon

repair geometry parameters, e.g., repair depth, length

and width, much less sensitive to component geometry

such as pressure vessels versus piping components, or

plate structures.

Downloaded From: http://proceedings.asmedigitalcollection.asme.org/ on 10/08/2014 Terms of Use: http://asme.org/terms

mailto:[email protected]


(2) Repair length has a significant effect on residual stress

distribution. Results to date suggest that a longer

repair is preferred than a short repair as far as residual

stress is concerned.

(3) The pre-existing original weld residual stresses have

very little influence on the repair residual stress

characteristics due to the dominant effects of repair.

As a result, residual stress modeling for weld repair

may ignore initial weld induced residual stresses

without introducing significant errors.

However, most of the investigations into repair weld residual

stresses have been carried out on a case by case basis for

specific applications. Recognizing some of the important

residual stress characteristic features that are unique to repair

welds, this paper aims to focus on effects of repair weld design

parameters so that recommendations on residual stress

mitigation can be provided for repair applications in practice.

This paper starts with a repair case study for validating the 3D

finite element residual stress analysis procedure to be used

throughout of the rest of the paper. The finite element modeling

procedure is then used to conduct an in-depth investigation of

repair weld geometry effect (repair depth, length and width) on

residual stress development. A residual stress decomposition

technique is used to quantitatively assess differences in residual

stress distributions as a result of change in repair weld

dimensions. Finally, recommendations on desirable repair

weld geometric attributes will be presented based on the

findings from this investigation.

2. MODELING PROCEDURE AND VALIDATION

2.1 Modeling Procedure Finite element modeling procedure developed by Dong and his

co-workers [7, 8-11] is used here. The procedure is based on

ABAQUS [18] and a unified weld material constitutive model

and extensively validated for various weld residual stress

modeling applications [18]. Detailed discussions on the theories

and numerical procedures can be found in [8-11] and are not

repeated here due to space limitations. Instead, only relevant

numerical procedures for this study described below.

2.2 Validation Detailed residual stress measurement data for a 432mm outer

diameter by 19.6mm thick pipe girth weld mock-up containing

offset weld repairs were available [17]. It has two repair lengths

which are 20º and 62º as shown in Fig.1(a). The short repair

with arc length of 20º is of interest for validation purposes.

Fig. 1(b) presents the repair weld geometry and the detailed

shape of each weld bead. Please note that depth of the weld

repair is about 14mm which is about 71% of the full thickness.

Fig. 1(c) indicates the measurement location at the -24mm

which is the weld toe of the repair weld.

Figure 1 (a) General arrangement shown circumferential positions of

short and long weld repairs, (b) short repair excavation profile with

schematic bead lay-up, and (c) position of neutron diffraction and deep

hole residual stress measurement (x = -24mm)

Fig. 2 shows a 3-D finite element model used in this study for

the short repair case (arc length 20º). The cross-section at mid-

length repair is exhibited in Fig 2(a) and (b). The profiles of

weld pass are modeled according to the descriptions given in

Fig. 1 (b). The total 3-D model is a quarter one, as shown in

Fig. 2(c), with two symmetry plane conditions – one plane is Z

symmetry and the other is X symmetry. Symmetry is used to

reduce the model size. Accurate residual stress profile can be

obtained in this validation study, since residual stress field

induced by the short repair weld is not influenced by the quarter

model [13]. The model was constructed with 80841 nodes and

72120 elements. Material is stainless steel 316. Von Mises yield

criterion following isotropic hardening law is used for this case

study and all parametric analyses reported in the following.

Figure 2 3-D finite element model for short repair (a) cross-section at

mid-length of repair (b) detailed weld pass profiles and position of

residual stress measurement, and (c) full finite element model

In performing welding heat flow analysis, each weld pass is

deposited simultaneously without considering moving-arc

effect. The deposition temperature is 1500°C. At and above this

temperature, all the material properties are assumed to be

constant except the thermal conductivity which is assumed to



be doubled in order to account for the enhanced convection

effect by the molten weld pool. After deposition of each weld

pass, the model is cooled down until whole model reached the

specified inter-pass temperature 160°C. The inter-pass

temperature is only considered in the validation study for the

specific requirement of stainless steel pipe welds. After the

final weld, the model cools down to room temperature. Normal

air convection is applied to the free surfaces. 8-Noded brick

element type of DC3D8 is used in the thermal analysis.

In the thermo-mechanical analysis, time dependent temperature

distributions determined in the thermal analysis are provided as

input as the driving force for residual stress development.

Accordingly, 8-Noded brick element type of C3D8R is used

with hourglass control. Rigid body motion is eliminated and

symmetry plane conditions are applied. An annealing

temperature for plastic strain is set to start at 1200°C as

demonstrated in a number of publications [10,19].

2.3 Modeling versus Experimental Results The position of residual stress measurement is at the weld toe

(WT), or heat affected zone (HAZ), of the repair as shown in

Fig. 1(c) and 2(b). Measurement data are obtained by using

neutron diffraction (ND) and deep hole (DH) techniques.

Comparison between measured [17] and FE predicted

distributions of axial and hoop stresses are depicted in Fig. 3. It

is evident that both ND and DH drilling provide a remarkable

consistent measurements for the through-thickness residual

stress distributions. As for the FE prediction, the agreement

with the measured data is good, expect for the axial stress, at

the first glance. However, the magnitudes of the decomposed

axial membrane and bending stresses are almost identical as

shown in Table 1. The only difference between FE predicted

and measured data for axial stress is the self-equivalent stress

which is likely to be the least significant in fracture mechanics

based structural integrity assessment, except for the small

length-scale cracks (usually for crack less than 10% of

thickness) [7,19]. For this reason, all the parametric results in

the following are summarized in terms of decomposed

membrane and bending stresses. For this case, as far as

membrane and bending stresses are concerned, the FE

modeling results and measurement data show a rather good

agreement.

Figure 3 FE results versus measurement data at the weld toe of mid-

length of the short repair (a) axial stresses, and (b) hoop stresses

Table 1 FE vs measured membrane and bending components of axial

and hoop stresses in Fig. 3

ND DH FE

Axial Membrane 178 198 172

Bending -75 -93 -50

Hoop Membrane 165 203 209

Bending -165 -124 -149

3. PARAMETRIC ANALYSIS With the modeling procedure validated in the previous section,

a series of parametric residual stress analyses are carried out to

examine the effects of repair depth, width, and length on the

general characteristics of residual stress distributions. Owing to

the 3-D nature of repair weld residual stress distribution, the

parametric analyses are carried out using 3-D solid finite

element models. Fig. 4 shows the definition of some

parameters. Through-thickness weld centerline (WCL) is

defined in the middle of weld, which is shown as the dashed

purple line in Fig. 4. For the sake of simplicity, idealized shape

of weld bead is used in the parametric analysis in order to

eliminate other variables. Please note the FE model is a quarter

one with the consideration of two symmetries with respect to

the length and width direction.

Figure 4 3-D FE model for parametric study of pipe repair welds (a

quarter model)

The repair weld parametric study has covered repair length

(half actual length in FE model due to symmetry) in angular

dimension from 20º to 100º, repair width (half actual width in

FE model due to symmetry) from t/2 to 2t, repair depth ranging

from t/5 to t, and pipe radius to thickness radio r/t from 2.8 to

12. In order to investigate a large number of parametric

analyses and support fracture mechanics based structural

integrity assessment, a length-scale based through-thickness

residual stress decomposition technique with respect to pipe

thickness is adopted, as shown in Eq. (1). By using decomposed

through-thickness membrane and bending stresses, effects of

various repair parameters on residual stress features can be

further characterized [7].



t

xx

dxxt

xt

dxxt

bmes

t

b

t

m

21)(

2)(

6

)(1

..

0

2

0

(1)

where t is pipe wall thickness and x is measured from pipe ID.

It has been shown by Dong [7] that membrane part σm and

bending part σb play a key role in contributing to fracture

driving force in fracture assessment while the contribution of

self-equilibrating part σs.e. is only limited to small crack regime.

Material used for parametric analyses is 2.25CrMo-V steel. Fig.

5 shows its temperature dependent properties which are

normalized with respect to their values at 23°C.

Figure 5 Temperature dependent material properties for

2.25CrMo-V steel

3.1 Repair Depth Effect Five repair depths are considered in this section to investigate

the effect of repair depth on characteristics of residual stress

distribution. The repair depths range from a shallow repair of

0.2t to a deep repair of the entire thickness (1t). The depth of

each repair weld metal is assumed to be 0.2t, e.g., 5 welds

deposited for the repair of the full thickness. All five repairs are

made from outer surface (OD) to inner surface (ID), which

corresponds to the most popular repair direction in practice. In

order to solely evaluate repair depth effect, repair width and

length maintain as constants for this set of analysis, which are

1t and 20o, respectively. Since the thickness of pipe is the same

for all cases (t=20mm), it is of importance to consider two r/t

ratios in order to differentiate thin and thick pipes.

3.1.1 Thin Pipe r/t=12 The contour plots of residual stress distribution for the thin-

shell r/t=12 repairs are shown in Fig. 6. It is clear to see that the

hoop residual stress is dominantly tensile in the outer section of

the repair area for all 5 repair cases. On the inner surface,

however, the hoop residual stress changes from low tension (or

neutral) to high tension as repair depth is increased. With regard

to the axial residual stress, the overall trend is similar to the

hoop residual stress. Although tensile stress on the outer surface

shows a slight change with the increase of repair depth, the

residual stress on the inner surface increases significantly. With

a shallow repair depth (0.2t), the axial residual stress on the

inner surface is slightly tensile and compressive in the middle

section. As repair depth is increased, the axial residual stresses

on the inner and middle surfaces become increasingly high in

tension.

Figure 6 Repair depth effect – Contour plot of residual stress

distributions (r/t=12)

Detailed through-thickness residual stress distributions along

WCL and weld WT are exhibited in Fig.7 and 8, respectively.

The results are presented varying repair depth from 0.2t to 1t.

The horizontal axis is measured from ID. The overall trend is

consistent with the observations from the contour plots. For

residual stress in hoop direction (Fig. 7a and 8a), it is clearly to

see that values of the first half thickness (from 0 to 10mm)

move towards higher stresses and overall residual stress

distribution becomes much flatter with the increase of repair

depth. This indicates residual stress bending component reduces

and membrane component increases as repair depth becomes

larger. While for the second half thickness (from 10mm to

20mm), all residual stress profiles maintain as the same for

different repair depths. In addition, for repair depth at 0.6t and

beyond, through-thickness residual stress distributions are

almost unchanged. Pretty much identical findings are shown in

Fig. 7b and 8b for axial residual stress distributions.



Figure 7 Repair depth effect – through-thickness residual stress

distributions at WCL for r/t=12: (a) hoop residual stress distributions,

and (b) axial residual stress distributions

Figure 8 Repair depth effect – through-thickness residual stress

distributions at WT for r/t=12: (a) hoop residual stress distributions,


In order to quantitatively evaluate repair depth effect

contributed to the through-thickness residual stress distributions

shown in Fig. 7 and 8, all decomposed membrane and bending

components according to Eq. (1) are plotted as function of

repair depth depicted in Fig. 9 and 10, respectively. The overall

trend is consistent with the observations from the through-

thickness plots. The membrane stress component (blue bars) for

both hoop and axial stresses are increased initially from shallow

repair (0.2t) to medium-depth repair (0.6t), and then stay

relatively unchanged for the rest of repair depths. Similarly, the

bending stress component (red bar) for both hoop and axial

residual stresses is decreased from shallow repair (0.2t) to

medium-depth repair (0.6t) and then stays relatively unchanged.

When repair depth reaches 0.6t or beyond, the through-

thickness residual stress distribution essentially remains

roughly the same upon further increase in depth. These results

provide a detailed substantiation of the general

characterizations on repair depth effects. As a result of this

study, it may state that a shallower repair tends to develop more

bending, less membrane stress than a deeper repair. Also for a

deeper repair, if a repair depth beyond half thickness,

membrane and bending stresses no longer change in any

significant manner.

Figure 9 Repair depth effect – decomposed residual stress

components at WCL for r/t=12: (a) hoop residual stress components,

and (b) axial residual stress components


components at WT for r/t=12: (a) hoop residual stress components,


3.1.2 Thick Pipe r/t=2.8 For r/t ratio smaller than 10, a pipe can be characterized as a

thick shell. Consider an extreme case, a pipe with r/t ratio of 2.8

is used to further investigate repair depth effect on residual

stress distributions. Since from a mechanics point of view, thick

shell may not have the same assumptions as those used in thin

shell. Please note that due to the difference in r/t ratio, the

absolute repair length measured in arc length is much shorter

than the previous case, even though the angular span of repair

length remains as 10o.

Similar observations are found in contour plots and line plots

compared to those shown for r/t ratio of 12. Decomposed

residual stress components along WCL are exhibited in Fig. 11.

The trend for membrane and bending stress components is

similar to the previous case. Both hoop and axial membrane

stresses increase as the repair depth increases from a shallow

repair (0.2t) to a medium-depth repair (0.6t), while the bending

stress component tends to decrease. After repair depth reaches

0.6t or beyond, both membrane and bending stresses remain

relatively stable. For WT location, same findings are also

observed.


components at WCL for r/t=2.8: (a) hoop residual stress components,


A comparison of r/t ratio effects on membrane and bending

stresses variations are studied by combining the results from

Fig. 11 (a thick pipe) with the ones from Fig. 9 (a thin pipe). It

can be observed that for small r/t ratio of 2.8, the magnitude of

axial membrane stress is larger while the hoop membrane stress

is smaller. This is primarily due to the increase of structural

rigidity in the model as a result of smaller r/t ratio. In addition,

if membrane and bending stresses of the two cases are plotted

as a function of r/t ratio, it can be seen that two curves are

parallel to each other. The plot is not shown here due to space



limitations. As such, r/t ratio can be characterized as an

independent parameter that controls residual stress distributions

as discussed in [22].

3.2 Repair Length Effect As discussed in [10-12], repair length is another important

parameter that can have a significant effect on residual stress

distributions. In this section, further expand the investigation on

the repair length effect using 3-D solid models is carried out.

The study will be conducted on both thin-shell (r/t=12) and

thick-shell (r/t=2.8) pipes. Three different repair lengths are

considered, which are 20o, 50

o, and 100

o respectively (half

repair span angles in FE model due to symmetry). In order to

isolate the length effect, repair depth is used as t/2 and width as

t (t/2 in FE model due to symmetry) for all repair length cases.

The repair weld metal is assumed to be deposited on OD in a

single pass layer.

3.2.1 Thin Pipe r/t=12 The contour plots of residual stress distributions for the three

different repair lengths on thin-shell r/t=12 pipe are shown in

Fig. 12. Similar to the results observed in the 3-D shell element

model [10], the 20o repair case shows a general characteristic of

residual stress distribution in short repair category in which the

axial residual stress in the middle section of repair is

aggregated by weld end effects. The 50o and 100

o cases are

more in the medium to long repair categories which tend to

show isolated weld end effects and relatively invariant

distribution along repair length direction within the rest of the

repair length.

Figure 12 Repair length effect – Contour plot of residual stress

distributions (r/t=12)

Detailed line plots of through-thickness residual stress

distribution are shown in Fig. 13 and 14 for WCL and WT

locations, respectively. Again the horizontal axis is measured

from ID. The results vary by different repair lengths. For

residual stress in hoop direction (Fig. 13a and 14a), it can be

clearly seen that stress values for the first half thickness (0-

10mm) are decreased with repair length increasing. While the

stress values for the second half thickness (10mm-20mm)

roughly maintain the same. This implies a reduced membrane

component and an increased bending component as repair

length increases. For axial residual stress (Fig. 13b and 14b),

residual stress distribution simply shifts to a lower magnitude

with increasing the repair length.

Figure 13 Repair length effect – through-thickness residual stress



Figure 14 Repair length effect – through-thickness residual stress



Membrane/bending stress components are exhibited in Fig. 15

and 16, which correspond to WCL (Fig. 13) and WT (Fig. 14)

locations, respectively. Overall trend is consistent with the

observations described in the line plots, which is membrane

stress decreases and bending stress increasing as repair length

increases. Along hoop direction, all repair welds show high

hoop membrane stress for the thin-shell pipe although the short

repair (20o) exhibits a slightly higher value in magnitude. As for

axial residual stress, membrane stress is much higher for the

20o repair than the 50

o and 100

o repairs at both WCL and WT

locations. Membrane stresses for 50o and 100

o repairs are

almost zero. As such, a longer repair is more favorable than a

short repair as far as residual stress management is concerned,

which is consistent to the finding in [10]

Figure 15 Repair length effect – decomposed residual stress








3.2.2 Thick Pipe r/t=2.8 For the case of thick pipe, r/t ratio of 2.8 is considered here

again. The same three different repair lengths are used to

conduct repair length effects, which are 20o, 50

o, and 100

o

respectively. The contour plots of residual stress distributions

for the thick-shell pipe are shown in Fig. 17. The results

indicate that, for thick-shell r/t=2.8 pipe, both 10o and 25

o

repair cases exhibit high magnitude of axial stress. This

suggests that 10o and 25

o repairs can be classified as short

repairs for r/t=2.8 pipe. For hoop stress, thick pipe shows a

strong compression at the weld toe, which indicates a higher

restraint condition compared to r/t ratio of 10.

Figure 17 Repair length effect – Contour plot of residual stress

distributions (r/t=2.8)

Decomposed residual stress components at the WCL are plotted

in Fig. 18 as a function of repair length. The overall trend of

residual stress component variations with repair length is

similar to the thin-shell pipe, except that the magnitude of

membrane stress component is significantly higher for the

thick-shell pipe than that observed for the thin pipe with r/t=12.

Again, the increase in membrane stress component for thick-

shell pipe repairs can be attributed to the increase of structural

rigidity in the repair area as a result of a smaller r/t ratio. In

addition, for along hoop direction, it is noticeable that

membrane stress has a slightly jump (about 100MPa) from

repair length 20o to 50

o. One possible reason is that the pipe is

too stiff to react when depositing such a small repair. For axial

residual stress, it can be seen that membrane stress reduces

significantly when repair length reaches to 100o. It is further

confirmed that a longer repair is more favorable than a short

repair.


components at WT for r/t=2.8: (a) hoop residual stress components,


3.3 Repair Width Effect In this study, the effect of repair width on residual stress

features is also investigated. Three different repair widths are

considered, with the total repair width equal to t/2, t, and 2t

respectively. Repair is assumed to perform on OD. Please note

that half of repair width is used in the FE model due to

symmetry with respect to the width direction (axial direction).

In order to isolate repair width effect from other repair

geometry parameters, the repair width models in this section

are created with the same repair depth (t/2) and a single layer of

weld metal deposition. Repair length is 25o angular span.

Again, both thin-shell and thick-shell pipes with r/t=12 and 2.8

are taken into consideration.

3.3.1 Thin Pipe r/t=12 The contour plots of residual stress distributions for the three

different repair widths on thin-shell r/t=12 pipe are shown in

Fig. 19. The axial residual stress on the inner surface has shown

the most significant impact with the magnitude changed from

low compression to high tension. Outer surface is always

subjected to compressive stress. In the hoop direction, the

repair width effect is less significant compared to the axial

direction, even though the magnitude to stress field slightly

decreases with repair width increasing.



Figure 19 Repair width effect – Contour plot of residual stress

distributions (r/t=2.8)

Fig. 20 and 21 exhibit the detailed line plots of through-

thickness residual stress distributions along WCL and WT,

respectively. Horizontal axis is from ID. As can be seen for

axial and hoop residual stresses, with increasing repair width,

stress values of the first half thickness (0-10mm) increase while

the stress values of the second half thickness (10-20mm)

roughly maintain the same. This is similar to the repair depth

effect. It is noticeable that for a narrow repair (2/t), axial

residual stresses are compressive on ID. This is primarily due to

the face that less total heat input to the structure than a wider

repair. The compressive stress on ID is good news from

Fitness-for-Service point of view. As a result, a narrower repair

should be preferred than a wider repair as far as residual stress

is concerned.

Figure 20 Repair width effect – through-thickness residual stress



Figure 21 Repair width effect – through-thickness residual stress



Through-thickness residual stresses depicted in Fig. 20 and 21

are then decomposed into membrane and bending stresses

according to Eq. (1) as shown in Fig. 22 and 23, respectively. In

general, membrane stress and the absolute value of bending

stress slightly increase as repair width increases. For the wide

repair case, the bending stress is more dominant in the axial

direction at both weld centerline and weld toe locations. Please

note that a negative bending stress in the diagram does not

mean a smaller value. It means a tension on the inner surface

and compression on the outer surface as the line plots shown in

Fig. 13b and 14b. The axial membrane stress is negligible

compared to its bending component. In the hoop direction, the

membrane stress component is dominant in the hoop direction

for all three repair widths. Hoop bending stress is also increased

as the repair width is increased, but to a less degree than the

axial bending stress. So again, it is evident that a narrower

repair is much more desirable than a wider repair.

Figure 22 Repair width effect – decomposed residual stress






3.3.2 Thick Pipe r/t=2.8 If r/t ratio of 2.8 is considered, a similar observation to that for

r/t of 12 can be made from Fig. 24 where decomposed residual

stress components at the WCL are summarized. As the repair

width is increased, the axial membrane stress is increased and

axial bending stress is changed from a tension on the outer

surface to a tension on the inner surface. It is not surprising to

see that the axial membrane stresses are much larger than the

ones in thin pipe due to an increased radial stiffness in thick

pipe while hoop membrane and bending stresses relatively

insensitive to repair width.




components at WCL for r/t=2.8: (a) hoop residual stress components,


4. CONCLUDING REMARKS In this paper, detailed parametric analyses are presented on

effects of repair weld geometry (depth, length, and width) and

component geometry (wall thickness and pipe to thickness

ratio) on resulting residual stress distributions. The results

clearly show repair weld geometry parameters are very

important to the control of residual stresses for fracture

mechanics based fitness for service assessment purpose. The

most desirable repair weld should be as long, as narrow, and as

shallow as practically possible for residual stress control

purpose. These geometric attributes may be referred to as

general rules for achieving an effective residual stress

mitigation by design.

ACKNOWLEDGMENTS The work reported here was supported by the National

Research Foundation of Korea (NRF) Gant funded by the

Korea government (MEST) through GCRC-SOP at University

of New Orleans under Project 2-1: Reliability and Strength

Assessment of Core Parts and Material System. The authors are

grateful to the encouragement and oversight of Project PI

Professor M. H. Kim during the course of this investigation.

REFERENCES [1] Dunn J, MacGuigan J, McLean RJ, Miles L, Stevens RS.

Investigation and repair of a leak at a high temperature

stainless steel butt weld. Proceedings of the international

conference on integrity of high temperature welds 1998;

241-258

[2] The Battelle integrity of nuclear piping (BINP) program

final report – Appendix G: Evaluation of reactor pressure

vessel (BPV) nozzle to hog-leg piping bimetallic weld joint

integrity for the VC summer nuclear power plant report

2005

[3] Gandy DW, Findlan SJ, Viswanathan R. Weld repair of

steam turbine casing s and piping – an industry survey. J

Strain Ana 2000; 35(4):287-305

[4] API Recommended Practice 579 RP. 2nd

Edition. American

Petroleum Institute 2007.

[5] BS 7910:2005, Guide to Methods for Assessing the

Acceptability of Flaws in Metallic Structures. British

Standards Institution 2005.

[6] Procedure R6 Revision 4, Assessment of the integrity of

structures containing defects 2013

[7] Dong P. Length scale in secondary stresses in fracture and

fatigue. Int. J. of Pressure Vessel and Fatigue 2008;

85:124-143

[8] Bouchard PJ. Validated Residual Stress Profiles for

Fracture Assessments of Stainless Steel Pipe Girth Welds.

International Journal of Pressure Vessels and Piping 2007;

84: 195-222

[9] Dong P, Zhang J and Song S., 2013 “Assessment of some

existing residual stress prescriptions for fitness for service

assessment of girth welds”, under review

[10] Dong P, Zhang J, Bouchard PJ. Effects of repair weld

length on residual stress distribution. Transactions of the

ASME 2002; 124:74-80

[11] Dong P, Hong JK, Bouchard PJ. Analysis of residual

stresses at weld repairs. Int. J. of Pressure Vessel and

Piping 2005; 82: 258-269

[12] Dong P, Cao Z, Hong JK. Final PVRC Residual Stress and

Local PWHT JIP Report on Investigation of Weld Residual

Stresses and Local Post Weld Heat Treatment 2005

[13] Elcoate CD, Dennis RJ, Bouchard PJ, Smith MC. Three

dimensional multi-pass repair weld simulations. Int. J. of

Pressure Vessel and Fatigue 2005; 82:244-257

[14] Keppas K, Wimpory RC, Katsareas DE, Anifantis NK,

Youtsos AG. Evaluation of residual stress assessment

methods using a repair weld benchmark. J. Strain Analysis

2010;45:197-208

[15] Brust FW, Scott PM, Yang Y. Weld residual stresses and

crack growth in bimetallic pipe welds. Proceeding of IIW

Conference, 2003

[16] Zeinoddini M, Arnavaz S, Zandi AP, Alizadeh Vaghasloo

Y. Repair welding influence on offshore pipelines residual

stress fields: an experimental study. Journal of

Constructional Steel Research 2013; 86:31-41

[17] Bouchard PJ, George D, Santisteban JR, Bruno G, Dutta M,

Edwards L, Kingston E, Smith DJ. Measurement of the

residual stress in a stainless steel pipe girth weld

containing long and short repairs. Int. J. of Pressure Vessel

and Fatigue 2005; 82:299-310

[18] ABAQUS version 6.11, 2012

[19] Dong P, Hong JK. Recommendations on Residual Stresses

Estimate for Fitness-for-Service Assessment. WRC

Bulletin 2003, No. 476, Welding Research Council, New

York

[20] Brust FW, Dong P, Zhang J. A Constitute for Welding

Process Simulation Using Finite Element Methods.

Advances in Computational Engineering Science 1997,

Proceedings of ICES Conference, pp. 51-56

[21] Dong P. 2001. Residual Stress Analysis of a Multi-Pass

Girth Weld: 3-D Special Shell Versus Axisymmetric

Models. Journal of Pressure Vessel Technology 2001;

123:207-213.

[22] Song S, Dong P and Zhang J., 2012 “A Full Residual

Stress Estimation Scheme for Pipe Girth Welds”,

Proceeding of ASME PVP Conference, Toronto, Ontario,

Canada, July 15-19, 2012

[23] Zhang J, Song S and Dong P, 2011 “Important Residual

stress Features in Reactor Nozzle Dissimilar Metal Welds”,

In: Proceeding of ASME PVP 2011 Conference,

Baltimore, Maryland, July 17-21, 2011. ASME, CD

Publication, ISBN 978-0-7918-4456-4; 2011.

Downloaded From: http://proceedings.asmedigitalcollection.asme.org/ on 10/08/2014 Terms of Use: http://asme.org/termsView publication statsView publication stats

https://www.researchgate.net/publication/269277560

Residual Stresses in Weld Repairs and Mitigation by Design · RESIDUAL STRESSES IN. WELD REPAIRS...

Documents

Transcript of Residual Stresses in Weld Repairs and Mitigation by Design · RESIDUAL STRESSES IN. WELD REPAIRS...