Research Papers: Materials and Fabrication

Gas Pipeline Failure Caused by In-Service Welding

[+] Author and Article Information
A. Farzadi

Department of Mining and
Metallurgical Engineering,
Amirkabir University of Technology,
Hafez Street,
PO Box 15875-4413,
Tehran 1591634311, Iran
e-mail: farzadi@aut.ac.ir

1Corresponding author.

Contributed by the Pressure Vessel and Piping Division of ASME for publication in the JOURNAL OF PRESSURE VESSEL TECHNOLOGY. Manuscript received October 28, 2014; final manuscript received August 18, 2015; published online October 6, 2015. Assoc. Editor: Xian-Kui Zhu.

J. Pressure Vessel Technol 138(1), 011405 (Oct 06, 2015) (9 pages) Paper No: PVT-14-1173; doi: 10.1115/1.4031443 History: Received October 28, 2014; Revised August 18, 2015

In the research presented in this paper, a failure analysis had been carried out to identify causes of an incident, which had taken place after an operation to repair a leak in an interstate natural gas pipeline. In this operation, a partial encirclement reinforcement (patch) was welded to the carrier pipe according to an available hot taping procedure, while gas was flowing in the pipeline. The failure analysis commenced with preliminary steps of information gathering of background data regarding the repair operation and then several samples were extracted for macroscopic and microscopic metallurgical examinations. In addition to fractographic analyses of fracture surfaces, pipe material was examined because the pipeline had been in service for prolonged period and there was not any official material information available. The analyses disclose that hydrogen-assisted cracking, wrong design of branch connection, paint coating, and pipeline operating conditions were major factors contributing to the failure. The work undertaken also included development and recommendation of a repair procedure to avoid similar failures in the future.

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Fig. 1

Crevice at welded junction of pig signaler and carrier pipe

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Fig. 2

Facilities used in repair operation

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Fig. 3

Changes in inlet gas pressure to the compressor station with time

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Fig. 4

Piece of pipe launched into the air, pig signaler, and regions A and B

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Fig. 5

Microstructure of the pipe steel showing ferrite and pearlite banding

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Fig. 6

Scanning electron micrographs of fracture surfaces obtained by impact testing at 0 °C

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Fig. 7

Macroscopic photograph of fracture surface in the regions (a) A and (b) B of the piece of pipe launched into the air

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Fig. 8

SEM fractographs of the piece of pipe launched into the air in the regions (a) A and (b) B

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Fig. 9

Optical micrographs in the (a) grain-coarsened, (b) grain-refined, and (c) partial grain-refined or intercritical regions of the HAZ

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Fig. 10

(a) Transverse cross section of the fillet weld showing weld beads, HAZ, crack, and hardness traverse and (b) hardness profile in the weld zone

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Fig. 11

Optical micrograph of (a) gas porosity in the weld metal and (b) minute cracks in the HAZ

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Fig. 12

Suggested welding sequence [20]




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