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Research Papers: Materials and Fabrication

Residual Stress State of X65 Pipeline Girth Welds Before and After Local and Furnace Post Weld Heat Treatment

[+] Author and Article Information
Yao Ren

Department of Mechanical,
Aerospace and Civil Engineering,
Brunel University/NSIRC,
London UB8 3PH, UK
e-mail: yao.ren@brunel.ac.uk

Anna Paradowska

ANSTO,
Sydney NSW 2232, Australia
e-mail: anp@ansto.gov.au

Bin Wang

Department of Mechanical,
Aerospace and Civil Engineering,
Brunel University,
London UB8 3PH, UK
e-mail: bin.wang@brunel.ac.uk

Elvin Eren

TWI Ltd.,
Cambridge CB21 6AL, UK
e-mail: elvin.eren@twi.co.uk

Yin Jin Janin

TWI Ltd.,
Cambridge CB21 6AL, UK
e-mail: yin.jin.janin@twi.co.uk

1Corresponding author.

Contributed by the Pressure Vessel and Piping Division of ASME for publication in the JOURNAL OF PRESSURE VESSEL TECHNOLOGY. Manuscript received August 17, 2016; final manuscript received January 27, 2017; published online March 10, 2017. Assoc. Editor: Xian-Kui Zhu.

J. Pressure Vessel Technol 139(4), 041401 (Mar 10, 2017) (8 pages) Paper No: PVT-16-1140; doi: 10.1115/1.4035884 History: Received August 17, 2016; Revised January 27, 2017

This research investigated the effects of global (in other words, furnace-based) and local post weld heat treatment (PWHT) on residual stress (RS) relaxation in API 5L X65 pipe girth welds. All pipe spools were fabricated using identical pipeline production procedures for manufacturing multipass narrow gap welds. Nondestructive neutron diffraction (ND) strain scanning was carried out on girth welded pipe spools and strain-free comb samples for the determination of the lattice spacing. All residual stress measurements were carried out at the KOWARI strain scanning instrument at the Australian Nuclear Science and Technology Organization (ANSTO). Residual stresses were measured on two pipe spools in as-welded condition and two pipe spools after local and furnace PWHT. Measurements were conducted through the thickness in the weld material and adjacent parent metal starting from the weld toes. Besides, three line-scans along pipe length were made 3 mm below outer surface, at pipe wall midthickness, and 3 mm above the inner surface. PWHT was carried out for stress relief; one pipe was conventionally heat treated entirely in an enclosed furnace, and the other was locally heated by a flexible ceramic heating pad. Residual stresses measured after PWHT were at exactly the same locations as those in as-welded condition. Residual stress states of the pipe spools in as-welded condition and after PWHT were compared, and the results were presented in full stress maps. Additionally, through-thickness residual stress profiles and the results of one line scan (3 mm below outer surface) were compared with the respective residual stress profiles advised in British Standard BS 7910 “Guide to methods for assessing the acceptability of flaws in metallic structures” and the UK nuclear industry's R6 procedure. The residual stress profiles in as-welded condition were similar. With the given parameters, local PWHT has effectively reduced residual stresses in the pipe spool to such a level that it prompted the thought that local PWHT can be considered a substitute for global PWHT.

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Figures

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Fig. 1

(a) Geometrical details of the weld groove and (b) schematic representation of the welding procedure

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Fig. 2

Principles of neutron diffraction

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Fig. 3

Overview of the comb reference specimen

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Fig. 4

Schematic overview of the welding procedure (left) and macrograph of the weld cross section and measurement points in the vicinity of the weld center (right)

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Fig. 5

Measurement of the axial residual strains in the pipe spool on KOWARI instrument at ANSTO

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Fig. 6

Sketch of the parameters for local circumferential PWHT

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Fig. 7

Calculated levels 1 and 2 through-thickness residual stress distribution based on BS 7910 and R6 [15,23]: (a) Longitudinal (hoop direction in pipe) stress distribution and (b) transverse (axial direction in pipe) stress distribution

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Fig. 8

Surface longitudinal residual stress distribution and calculated radius of the yield zone at butt weld in the pipe

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Fig. 9

Residual stress maps in as-welded condition in hoop (a) and axial (b) directions for PAW1 and PAW2

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Fig. 10

Residual stress maps in after PWHT in hoop (a) and axial (b) directions for PHT1 and PHT2

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Fig. 11

Comparison of the through-thickness residual stresses at weld center and weld toe before and after local and furnace PWHT with R6 and BS 7910

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Fig. 12

Comparison of the near outer-surface residual stress before and after local and furnace PWHT with R6 and BS 7910-PWHT: (a) Normalized hoop residual stresses and (b) normalized axial residual stresses

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