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 In a letter made public Tuesday, an investigator at the forensic engineering firm Exponent said the pipe appeared to have ruptured along a "crack-like flaw" that ran for several feet along a welded seam.
"But for this significant pre-existing crack-like flaw, it is my opinion at this point in time that the pipe would not have ruptured at this specific location on July 18," said Exponent's principal engineer, Robert D. Caligiuri.
He added that the flaw appeared to be old enough and large enough that Con Ed should have detected it sooner. His letter didn't say whether he believes the flaw was a manufacturing defect, or a problem that developed over the pipe's many decades underground.
Caligiuri's findings were immediately assailed as "misguided" by Consolidated Edison, which owns and maintains the steam delivery network.
Con Ed spokeswoman Elizabeth Clark said there was no crack or flaw in the pipe prior to the blast. She said the "flaw" identified by Caligiuri was an ordinary weld, "common in all forms of steel infrastructure."
"The weld in this instance in no way contributed to the rupture," she said in a written statement. "The weld described in the letter was forced open when the rupture occurred; it was not the cause of the rupture."
Con Edison has hired its own forensic engineering firm, Lucius Pitkin Inc., to help find the cause of the explosion. It has yet to issue a final report, but has previously told the utility it doesn't believe the pipe had degraded prior to the blast.
The explosion occurred in a busy intersection near Grand Central Terminal following a heavy rain. It tore a crater in the street, smashed windows, hurled debris at pedestrians and engulfed a tow truck carrying two people, both of whom were horribly burned. A woman also died of a heart attack.
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 Caligiuri questioned whether any other old steam pipes in use beneath city streets have similar defects.
Con Edison has insisted that its steam delivery system, which throbs below much of midtown Manhattan, is safe.
More investigation is needed, Caligiuri said, "to more fully assess the broader integrity of the steam system, and in particular to determine if other portions of the pipe network are susceptible to a similar failure."
Exponent was hired by the legal team representing the tow truck driver, Gregory McCullough, and his passenger, Judith Bailey. McCullough is still hospitalized.
"Why didn't Con Ed discover this problem, and why didn't they fix it?" said an attorney for the pair, Kenneth Thompson.
In his brief report on the blast, Caligiuri said much about the explosion remains unknown.
The primary cause of the rupture, he said, appeared to be a sudden buildup in pressure within the pipe, which then burst through the flawed section. What caused that pressure surge, however, is still unclear, he said.
[Associated Press; by David B.
Caruso]
Copyright 2007 The Associated Press. All rights reserved. This
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