Liberty Property Trust has paused assembly of the upper-most portion of the Comcast Technology Center tower to inspect the metal being used in that part of the structure for potential cracks.

John Gattuso, Liberty's regional director, said in an interview late last week that between 35 and 40 possible "indications" of cracking were found in the steel being used to construct the two-story-high frame that will house the CTC's lighting and mechanical systems atop the building's 60 occupiable stories.

Any cracking is thought to have occurred during the steel's galvanization process and is easily repaired, Gattuso said.

"This is not rare, but it's not totally common," he said. "It's not a catastrophic issue."

The inspection comes about a year before Liberty anticipates completing what will be the tallest building in the United States outside New York or Chicago. Other work will continue during the inspection, so the probe should not affect that schedule.

Planned for the $1.5 billion building, at 18th and Arch Streets, are offices and labs for Comcast Corp.'s growing workforce of technologists, engineers, and software architects, as well as studios for its local NBC and Telemundo affiliates and a Four Seasons hotel. A floor of the building also has been carved into condo units purchased by Comcast chief executive Brian Roberts and his wife, Aileen.

The inspection began a few weeks ago and will continue for another month to include the examination of each of the 5,200 welds binding 621 separate pieces of steel being assembled to support the building's lighting and mechanical equipment, Gattuso said.

The possible instances spotted so far may be merely surface markings, but any actual cracks that are found can be repaired by drilling holes into the base of the fractures to arrest their growth, he said.

The cost of the inspection and any other associated expenses will be borne by the supplier of the metal, SteelFab Inc. of Charlotte, N.C.

A message left with SteelFab was not immediately returned.