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Research Papers: Materials and Fabrication

Estimation of Maximum Pressure Stress Intensity in a Welding Tee

[+] Author and Article Information
Martin Blackman

Xtrados Pty Ltd.,
Perth 6000, Western Australia, Australia
e-mail: mblackman@xtrados.com

Contributed by the Pressure Vessel and Piping Division of ASME for publication in the JOURNAL OF PRESSURE VESSEL TECHNOLOGY. Manuscript received July 2, 2017; final manuscript received November 22, 2017; published online January 25, 2018. Assoc. Editor: San Iyer.

J. Pressure Vessel Technol 140(2), 021402 (Jan 25, 2018) (7 pages) Paper No: PVT-17-1119; doi: 10.1115/1.4038721 History: Received July 02, 2017; Revised November 22, 2017

The required thickness of welding tees is neither specified in ASME (2012, “Factory-Made Wrought Buttwelding Fittings,” American Society of Mechanical Engineers, New York, Standard No. B16.9-2012) nor is a clear calculation method provided in codes such as ASME (2016, “Process Piping,” American Society of Mechanical Engineers, New York, Standard No. B31.3-2016). This can lead to uncertainty regarding the pressure capacity of a tee fitting, particularly one that has suffered from erosion or corrosion. Code methods including area replacement (ASME, 2016, “Process Piping,” American Society of Mechanical Engineers, New York, Standard No. B31.3-2016) or pressure-area (ASME, 2015, “Boiler and Pressure Vessel Code Section VIII Division 2,” American Society of Mechanical Engineers, New York, Standard No. BPVC-VIII-2-2015; BSI, 2014, “Unfired Pressure Vessels Part 3: Design,” BSI, London, UK, Standard No. BS EN 13445-3) do not directly account for the effect which the curvature of the crotch region may have on the stress state in the tee. The approach adopted in this work is to liken the geometry of the tee crotch to the intrados of a torus or pipe bend. The shell theory applicable to the torus is adapted for the tee in order to derive a relationship for circumferential membrane stress. An equivalent tube radius is assigned by determining the local radius of shell curvature in the plane passing through the crotch center of the curvature. The actual stresses in the tee crotch are significantly reduced by the adjoining straight portions. This effect is difficult to quantify theoretically and has thus been investigated by means of finite element analysis (FEA)-based assessments. An empirical relationship was then established providing a conservative correlation between the theoretical stresses and the program calculated local stress intensities.

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References

Paulin Research Group, 2012, “FETee (FE/Pipe 6.5),” Paulin Research Group, Houston, TX.
Annaratone, D. , 2007, Pressure Vessel Design, Springer-Verlag, Berlin. [CrossRef]
ANSYS, 2015, “ANSYS 16.0,” ANSYS, Canonsburg, PA.
Stonehouse, M. , Becht , C., IV., Becht , C., V , and Paulin, T. , 2014, “Burst Tests of B16.9 Welded Tees,” ASME Paper No. PVP2014-28265.
BSI, 2007, “Butt-Welding Pipe Fittings—Part 2: Non-Alloy and Ferritic Alloy Steels With Specific Inspection Requirements,” The British Standards Institution, London, Standard No. BS EN 10253-2. https://shop.bsigroup.com/ProductDetail?pid=000000000030011252
Xuan, F.-Z. , Wang, C. , and., and Li, P.-N. , 2005, “Experimental Investigation of the Limit Load of the ANSI B16.9 Tees With and Without Cracks Under Internal Pressure,” East China University of Science and Technology, Shanghai, China.
WRC, 1988, “A Review of Area Replacement Rules for Pipe Connections in Pressure Vessels and Piping,” Welding Research Council, New York, WRC Bulletin No. 335.

Figures

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Fig. 3

View of fetee model

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Fig. 4

Stress intensity-membrane. fetee results (model 20).

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Fig. 5

Stress intensity-membrane plus bending, inside surface. fetee results (model 20).

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Fig. 6

Stress intensity-ANSYS model DN 600 × 450 tee, 19 mm thk, 65 mm crotch radius. Maximum stress intensity 127 MPa.

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Fig. 2

Cross section on xy plane, with cutting plane shown through the center of curvature. For simplicity, x is shown aligned with the header longitudinal axis in this view.

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Fig. 1

View of tee looking into branch

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Fig. 7

Linearized stress intensity-ANSYS model DN 600 × 450 tee, 19 mm thick, 65 mm crotch radius. Membrane stress intensity 103 MPa.

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