SAN FRANCISCO — In a formal audit just months before the deadly San Bruno blast, PG&E failed to tell state regulators about manufacturing defects affecting more than 80 miles of gas pipelines, according to evidence presented Friday in the utility’s federal criminal trial.

Calvin Lui, a supervising engineer in pipeline risk management who began working at PG&E in 2008, was the sole witness Friday. Lui was shown internal documents indicating that the utility was aware of wide-ranging threats to its pipeline system before participating in a state Public Utilities Commission audit of the aging network.

The PG&E documents showed the utility knew in early 2010 that 84 miles of pipeline, comprising 443 pipe segments, had manufacturing defects. The PUC pipeline audit took place in May 2010. In September of that year, a gas line beneath San Bruno ruptured, killing eight people and leveling dozens of homes.

Federal prosecutor Hallie Hoffman asked Lui several times if PG&E officials present for the audit ever notified or alerted auditors about the defects.

“No,” Lui replied each time.

In earlier testimony, William Manegold, a PG&E risk assessment supervisor, testified utility executives advised engineers on what kind of information they should provide PUC auditors.

“We were told not to answer questions that we weren’t asked by the PUC,” Manegold told the court.

In the years leading up to the explosion, Lui testified, engineers for PG&E operated as if they were unclear about whether federal regulations would allow them to spike pressures on older lines such as Line 132, the pipeline that burst beneath San Bruno.

“The pipeline codes tended to conflict and to confuse us,” Lui said.

Lui said that confusion existed even though PG&E engineers had widely circulated among themselves clear-cut rules from the Pipeline and Hazardous Materials Safety Administration. Those rules require operators to conduct pressure tests or inspections on any pipes in which the maximum pressure has been exceeded.

However, evidence presented by prosecutors showed that PG&E sought to skirt those rules. When inspections of certain older pipes were required, the utility promoted external corrosion observations as a cheaper alternative to more costly procedures such as high-pressure water tests or sending robots into the lines to inspect the pipes, according to internal company memos and prosecution witnesses.

Prosecutors told the judge after the jury had departed for the day that they expect to call no more than three more witnesses and anticipate they will conclude their case by Wednesday.

Among the upcoming prosecution witnesses are Sandra Flores, an FBI special agent; and Ravindra “Ravi” Chhatre, a National Transportation Safety Board investigator-in-charge who led the agency’s probe of the San Bruno explosion.

San Francisco-based PG&E faces 13 criminal counts, including 12 alleged violations of violating pipeline safety rules and one that it obstructed the NTSB investigation. PG&E has pleaded not guilty to all the charges and could be fined $562 million.

Contact George Avalos at 408-859-5167. Follow him at Twitter.com/georgeavalos.