Corrosion had eaten away nearly half of the metal wall of a pipeline that ruptured and spilled up to 101,000 gallons of crude oil along the Santa Barbara coast last month, federal regulators said Wednesday.

The preliminary findings released by the federal Pipeline and Hazardous Materials Safety Administration provide the first details about the integrity of the ruptured pipeline but do not point to a cause for the failure.

Regulators said an inspection by third-party metallurgists revealed metal loss of greater than 45% of the pipe wall’s thickness in the area of the break.

That level of corrosion alone does not explain why the pipe failed, said Richard B. Kuprewicz, a pipeline incident investigator with 40 years’ experience who is not involved in this investigation. He said external corrosion is common and can be managed by adhering to a rigorous inspection and monitoring program.

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