The Maintenance and Integrity of Thick Walled Pressure Vesls by Using
Temper Bead Welding Technique
R.N. Ibrahim, Department of Mechanical Engineering, Monash University
T. Shehata, Department of Mechanical Engineering, Monash University
cad2006
Abstract
This paper investigates the Temper Bead welding (TBW) technique using the Flux Cored Arc Welding (FCAW) process. The FCAW process increas productivity, improves welding efficiency and provides a more cost-effective method of Temper Bead Welding (TBW) repairs compared with the other commonly ud TBW techniques such as manual metal arc welding (MMAW) and gas metal arc welding (GMAW) which u solid wire. An automatic welding rig was created so that the TBW process could be tested using flux cored wire under different conditions. An experimental investigation was conducted to find the optimal welding parameters of the TBW using FCAW. This experimental investigation was done in order to provide the desired mechanical properties and microstructures without Post-Welding Heat Treatment (PWHT).
Due to the difficulties encountered in the determination of residual stress, the weld penetration depth into the ba material was ud as a guide to control residual stress. In this study, analytical solution was ud to support the u of TBW to repair damaged structures. This solution was bad on statistical and experimental data. The data were ud to establish the relationships between the technological parameters of TBW and the factors responsible for the quality of the required structure.
Keywords: Temper bead welding, Flux cored arc welding, Solid wires, Post welding heat treatment, Manual metal arc welding, Gas metal arc welding and Penetration
Introduction
According to the ASME standard, the conventional repair welding for wall steel constructions, which have a thickness of more than 40 mm requires PWHT to achieve the desired microstructure properties. The microstructure of the welding surrounded area is affected by the heat of the welding process. This affected area is known as the heat-affected zone (HAZ). The desired microstructure properties of HAZ are the properties which are as clo as possible to the parent material properties. For some structures, however, PWHT is very expensive or difficult. Publications to date [1,
2], have shown that the temper bead welding (TBW) can provide the desired microstructure properties of the welding without PWHT. The TBW provides that satisfactorily and solid wire welding process such as MMAW or GMAW are applied to TBW successfully.
TBW is ud to heat-treat the welded part or parts during the welding process instead of PWHT. TBW employs a multiple-pass deposition of the welding metal. Each layer of beads provides heat for the thermal treatment of the microstructure of the previous weld bead or the layer, as shown in figure 1. TBW techniques have been ud successfully for a number of repairs in USA and Canada, by using manual metal arc welding (MMAW) process or gas metal arc welding (GMAW) process, and its u is accepted and specified by the ASME Boiler and Pressure Vesl codes [3].
The quality of the temper bead-welding repair is very nsitive to some welding parameters [2] specific to the welding process employed. The parameters are the welding position and its effect on the bead shape, the bead deposition quence, the welding current,the traver speed, the arc length, the wire feeding speed, the torch angle, the preheat and inter-run temperatures and the heat inputs.
Figure 1. Two-layer ction shown schematically exhibiting approximately 85% refinement of the first layer coar grained HAZ by the cond layer [3].
There are veral industry-attractive aspects of TBW that need further investigation.One of the is the application of the flux-cored arc welding (FCAW) process that us hollow welding wire filled with flux. There has been limited rearch into the effectiveness of this process [2,3] but a preliminary study [4 and 5] indicates that FCAW might have a number of advantages over the commonly ud solid wires such as MMAW or GMAW process. The welding parameters that can provide the required microstructure and minimum residual stress in thick walled weldments need to be established to validate the application of flux cored arc welding (FCAW).
The Relationship between the Welding Parameters and the Depth of Penetration
The depth of penetration is a direct result of the welding heat input. It is necessary to have a desirable depth of penetration to gain sufficient bonding between the parent material and the welding material. Normally, the process of quickly heating and cooling the welding region is associated with residual stress and different grain sizes across the HAZ. The welding heat source is the applied electrical power (E) and the amount of the welding heat input (H) depends on the welding traver speed (v ) along the parent material beside the applied electrical power.
E = I * V * η Watt---------------------------------------------( 1 )Where
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I is the welding electrical current in Amp,
V is the welding voltage in volt and
η is the electrical power transmission efficiency.
(η) can be considered equal one in ca of measuring I and V as clo as possible to the welding spot.
Welding heat input can be calculated by applying equation (2)
H = (0.06 * I * V) / v kJ/mm----------------------------------------( 2 )B - Maximum fusion boundary, II - layer
U - Maximum fusion boundary, I layer
C - average layer height, I -layer
R - Maximum depth of refining zone, II-Layer .---Weld metal ---Coar Grained HAZ ---Fine Grained HAZ ---Partial Transformation
Where
v is traver speed in mm/min
In the FCAW process, the welding electrical current (I) is adjusted automatically according to the wire feeding speed. The welding voltage adjusted for the welding electrode size. It is clear, therefore, that the effects of (I) and (V) are limited and controlled, which means that the traver speed (v) has the main effect on the welding heat input (H). Another parameter that should be considered is the arc length (A). The (A) reprents the intensity of the welding heat source.
Experimental work
The investigation was conducted by using the automatic welding rig shown in figure 2. The traveling mechanism (A) was operated with constant speeds varying from 120
mm/min to 700 mm/min. The wire feeding system (15) was operated at 820 to 5600 mm/min. The welding machine (B) was worked at up to 400A.
Experimental data was collected to study the relationship between the depth of penetration and the welding main parameters as prented in Table 1. The welds were divided into three groups, Group
1, Group 2 and Group 3. In each group only one parameter was changed. For Groups 1 and 2 the arc length was changed, for Group 3 the traver speed was changed. Two different gas were ud in the manufacturing of the welds, for Groups 1 and 3, Argon Shield 100 gas was ud, but for Group 2 CO2 gas was ud. Commercially manufactured C-Mn steel plates of 10 and 12 mm thickness were ud for all welds in this investigation. A steel plate of 12 mm thickness was ud for Groups 1 and 2, but a plate of 10 mm thickness was ud for Group 3. The voltage for Groups 1; 2 and 3 were 30, 29 and 29 volts respectively. The electrical current for welds of Groups 1; 2 and 3 were 350, 380 and 380 respectively. The weldments (e Table 1) were manufactured using the basic flux-cored wire (AWS A5.20:E70T-4).
Table 1. The temper bead welding carried out using different Shield gas and Traver speeds.
Group No.Pass No.Traver Speed
mm/min.Arc length (A)
mm.
Penetration (P)
Mm.
11
2
3620
620
620
25
29
23
5
4.5
6
24
5
6620芳华观后感
620
620
23
28
25
4.5
4
5
37
8
母亲节礼品91000
253.5
600
25
25
25
4
8
6
1500
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Figure 2.
A) Traveling mechanism B) Welding machine C) 12-channel chart recorder.
D) Real time-temperature chart recorder.
E) Preheating elements controller.
1. 240V low speed motor.
2. Fine current control for motor.
3. Travel speed gauge.
4. Frame carriage.
5. Steel wheels.
6. Gear.
7. Variable head. 8. Welding torch. 9. Work piece.
10.Electrical heating elements. 11. Main frame. ( horizontal beam)
12. Main frame. ( Supporting legs) 13. Table 14. Welding lead.
15.Welding wire feeding system.银行柜员工作总结
Results and Discussion
By applying Merit Function “ χ2 “ on Groups 1 and 3, a mathematical relationship between the depth of penetration (P) as output and the traver speed (v) and the arc length (A) as inputs can be prented as following:
P = -0.0054 v + 0.93 A - 0.023 A2 (3)
咸鸭腿怎么做好吃From equation (3), the relationship between the depth of penetration (P) and either the traver speed (v) at different arc lengths or the arc length (A) at different traver speeds can be plotted as shown in Figures (3) and (4) respectively.
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of welds (groups “1” and “3”, Argon Shield 100 gas).
The relationship between the depth of penetration (P) and the arc length (A) at different traver speeds (as shown in Figures 3 and 4) demonstrates that a decrea in the traver speed at the same arc length is associated with an increa in the depth of penetration. Between arc length 5and 20.22 mm, any increa in the arc length at the same traver speed is associated with an increa in the depth of penetration. Therefore, with increasing heat, the spark heat, more heat transfers through the parent material. In the ca of the small arc length, the welding torch absorbed a fraction of the heat. The heat conductivity of the torch material is higher than that of the low carbon steel, so less heat transfers to the parent material. Also at this stage, the same penetration was achieved when an increa in the arc length was associated with an increa in the traver speed. Furthermore, any increa in the arc length between 20.22 and 30 mm was associated with a decrea in the depth of penetration as the surrounding ambient absorbs more heat.
A comparison of the results from [4&5] for FC wires and the results from [7] for solid wires, reveals that FC wires achieved deeper penetration for the same welding conditions (heat input, arc length and traver speed). Therefor if the same welding conditions, to achieve the same depth of penetration, then FC wires should be operated in faster speed than the solid wire. Therefore, the FCAW process can provide higher productivity than solid wire process.
Conclusion
Using FCAW process with TBW technique will increa the productivity, improve welding operation and efficiency and provide a more cost-effective method of weld repairs to the industry in comparison with the other commonly process known with TBW technique such as MMWA and GMAW.
Reference
[1] Lundin,C.D., "Overview of Results from PVRC Program on Half-Bead / Temper-Bead / Controlled Deposition Technique for Improvement of Fabrication and Service Performance of Cr-Mo Steel", 1996, WRC Bulletin 412, p. 16 - 26.
[2] Lau, T. W., Lau M. L. et al., "Development of Controlled Deposition Repair Welding Procedures at Ontario Hydro", 1996, WRC Bulletin 412, p. 35 - 42.
[3] Edgley J. S. and Pitrun M., "The Temper Bead Weld Repair of the Hazelwood Steam Drums", Pressure Vesls and Pipwork Conference, Sydney April 27 - 28, 1993.
[4] Ibrahim R. N., and Shehata T., "Effect of Flux Wire on Tempered Bead Welding Technique to Rep
air Damaged Carbon Steel Structure", ICM8, 8th International Conference on the Mechanical Behavior of Materials, Canada, British Colombia, May 16 - 21, 1999. [5] Ibrahim R. N., and Shehata T., "Effect of Welding Operation Parameters on the Depth of Penetration in Flux Cored Arc Welding Applications", 9th International Conference on Pressure Vesls Technology, Australia, Sydney, April 9 - 14, 2000.
[6] Sato, M., Suda, K. et al., “How to Weld Using Flux Cored Wires” Journal of Japan Welding Society, 1996, 65, (6), p. 13 – 20.
[7] Ahmed, N. U. and Jarvis, B. L., “The effect of welding condition on the thermal cycles in single electrode submerged arc welding” Australian welding journal, V43, 3rd. Quarter 1998.
