A Mashpee woman was convicted on Monday in federal court of having embezzled some $145,000 over eight years from the Steamship Authority.

Armine E. Sabatini, 46, pleaded guilty before Chief U.S. District Judge Mark L. Wolf to two counts of embezzlement and two counts of wire fraud.

She is scheduled for sentencing on Nov. 17, and faces up to 20 years in prison and up to $250,000 in fines on each of the wire fraud counts and up to 10 years and $250,000 on each of the embezzlement counts.

The court was told that between about October 2001 through to about September 2009, Ms. Sabatini, an SSA bookkeeper, conducted about 380 fraudulent refund transactions.

She did it by creating fictitious customer names of SSA customers, then assigning refund credits to them. Those refunds were paid into credit or debit card accounts she controlled.

The long-running fraud was investigated by the Federal Bureau of Investigation with assistance from the Falmouth police, after first coming to light on Sept. 23 last year when Mary Claffey, director of information technology at the boat line, noticed two almost identical refunds.

The first was a valid one to a customer’s Mastercard at 3:13 p.m. Six minutes later, Ms. Sabatini had processed another refund for the same amount, to the same customer name but on a different credit card.

Subsequent investigation by SSA staff showed a total of almost $10,000 had been credited to the same Visa card since June, by way of 10 refunds. When SSA staff contacted the bank which had issued the card, Steamship Authority general manager Wayne Lamson said, it would not give the name of the cardholder, but confirmed Ms. Sabatini’s name when it was suggested.

“The more we looked into it and other transactions, we saw a pattern and began to put things together,” he said, when first announcing the discovery of the embezzlement.

There was a pattern in which a refund would be credited to a genuine customer’s credit card. Then, some time later the customer’s name would appear again, but with a different credit card number.

When SSA management confronted Ms. Sabatini with their evidence, Mr. Lamson said, her reply was: “Just write down the amount I owe you and I’ll write you a check.”

The boat line terminated her employment a couple of days later and began going back through years of records of refunds.

“We were totally shocked by all this,” Mr. Lamson said. “She’s a 20-year employee, started with us in 1988. She was a bookkeeper for at least the last eight or nine years.”

Although the names of some real customers were used, none of them lost any money.

The SSA has since changed its refund procedure under which the staff member initiating a refund cannot also approve it.