Research Papers: Materials and Fabrication

Mathematical Approaching and Experimental Assembly to Evaluate the Risks of In-Service Welding in Hot Tapping

[+] Author and Article Information
Ivo Andrei de O. L Lima

Braskem S.A.,
Camaçari 42810-000, Bahia, Brazil
e-mail: ivo.lima@braskem.com

Alex Alisson Bandeira Santos

SENAI CIMATEC—Integrated Center of
Manufacturing and Technology,
Salvador 41650-010, Bahia, Brazil
e-mail: alex.santos@fieb.org.br

Contributed by the Pressure Vessel and Piping Division of ASME for publication in the JOURNAL OF PRESSURE VESSEL TECHNOLOGY. Manuscript received December 27, 2014; final manuscript received August 28, 2015; published online October 8, 2015. Assoc. Editor: Xian-Kui Zhu.

J. Pressure Vessel Technol 138(2), 021403 (Oct 08, 2015) (11 pages) Paper No: PVT-14-1213; doi: 10.1115/1.4031506 History: Received December 27, 2014; Revised August 28, 2015

The welding onto in-service pipeline (operation condition) results in three possibilities of high risks: leaking and/or explosion by burn-through, chemical reactions to instability, or even explosion due to the heat on internal fluid and cracking in heat affected zone (HAZ). The numerical methods have a useful role in the assessment of welding conditions for the safe in-service welding of pipelines. Only limited published works have considered direct calculation of burn-through using a combination of thermal and stress analysis. The mathematical model of the heat source is the most important part of these numerical models, and actually the mathematical model which described better the heat distribution of the arc welding through gas-shielded tungsten arc welding (GTAW) process or shielded metal arc welding process is the double ellipsoidal heat source (DEHS) model of Goldak and Akhlaghi (2010, Computational Welding Mechanics, Springer Books, New York, pp. 32–35). However, that model has considered the heat source in rectilinear motion only, and it depends on three parameters (a, b, c) which are related with the weld bead size and shape to define the geometry and co-ordinates of heat source, and they are determined empirically or experimentally. Few researchers published works that could determine these parameters mathematically, from the welding data. The publication that best analytically addressed this issue was the work of Eagar and Tsai (1983, “Temperature Fields Produced by Traveling Distributed Heat Sources,” Weld. J., 62(12), pp. 346–355). First, this paper presents a new equation for heat source in double ellipsoid considering the circular motion, trying to develop a model closer to the physical situation of hot tapping onto pipeline. Second, a proposal for determination of the parameters a, b analytically from the Eagar model and Tsai (1983, “Temperature Fields Produced by Traveling Distributed Heat Sources,” Weld. J., 62(12), pp. 346–355), and third, an experimental facility to get the temperature field that was used to validate the numerical finite element models.

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Fig. 1

Model of double ellipsoid of Goldak and Akhlaghi [7]

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Fig. 2

Gaussian heat source

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Fig. 3

Cylindrical coordinates for pipe model

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Fig. 4

Coordinate system used for DEHS in rectilinear movement (a) and circular movement (b)

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Fig. 5

Experimental models 1 and 2 and your numerical models, respectively

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Fig. 6

(a) Plant view and cross section of the model 1, (1) metal base and (2) vertical plate. (b) Plant view and cross section of the model 2.

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Fig. 7

Experimental and numerical values for the thermocouples TP-3 up to TP-8 during the first and second pass—Model 1

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Fig. 8

Experimental and numerical values for the thermocouples TP-7 and TP-8 during the first pass—Model 2

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Fig. 9

Width (a) and depth (b) for T joint

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Fig. 10

Equivalence between surface areas

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Fig. 11

Finite elements mesh of the tubular model

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Fig. 12

Boundary conditions

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Fig. 13

General view and main components

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Fig. 14

The proposed numerical model can predict the burn-trough risk with 120 A. The numerical model showed the equivalent stress above the yield stress at 80% of the cross section.

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Fig. 15

The proposed numerical model can be predicted which there will not burn-through with 80 A. The numerical model showed the equivalent stress above the yield stress at less than 5% of the cross section.




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