Abstract
On 6 July 2004, two parallel-running gas pipelines (18-inch and 24-inch diameters), in the main
transmission network of SNGPL (a gas company in Pakistan) were ruptured. The ruptures
occurred in the early hours of the morning about 8 miles downstream of the compressor station
AC-4. The ruptures were indicated by the increased gas flow at the outlet of AC-4 [1], first at
about 0648 hours and then again about 20 minutes later. The gas escaping from the ruptured lines
had caught fire, and the flames had also ‘affected’ a third parallel-running pipeline of 30-inch
diameter, lying next to the 24-inch line.
The metallurgical examination of the two ruptured lines showed that the 24-inch line was ruptured
with the help of an explosive device that had been placed on the underside of the pipe. An
examination of the 18-inch line showed that this pipe had failed as a result of the heating of the
pipe-wall, presumably, by the flame emanating from the 24-inch line. These two observations
clearly suggested that the 24-inch line was the first to rupture (by explosives), and the fire
following this rupture had heated the 18-inch pipe to a temperature where its yield strength was
unable to support the inside gas pressure. The 20 minutes time interval between the two ruptures
was obviously the time taken by the 18-inch pipe to be heated upto the level where it started to
yield.
The 30-inch line lying next to the 24-inch line was affected to the extent that its coating had been
burnt-off over a length of about 40-50 feet. However, the pipe did not exhibit any signs of deshaping or deformation what-so-ever. A replica metallographic examination indicated that the
microstructure of the pipe was not measurably affected by the heat. It was thus decided not to
replace the ‘affected’ part of the 30-inch pipe, but only to re-coat this affected portion.
F. Hasan, F.Ahmed. (2007) Metallurgical Analysis of High Pressure Gas Pipelines Rupture, Pakistan Journal of Engineering and Applied Sciences, Volume 1, Issue 1.
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