The city will redesign and replace portions of 15 metal “canopy arms” that were erected at three rail stations after flaws were discovered in similar arms that were fabricated for the rail line, according to the Honolulu Authority for Rapid Transportation.

Andrew Robbins, executive director for HART, said the new push to redesign and install all of the station canopy arms by December is an effort to stick to the scheduled interim opening of the stretch of rail line from East Kapolei to Aloha Stadium by the end of next year.

Rail officials had expressed concern that problems with the canopy arms might delay that interim opening, but Robbins said HART directed the engineering company AECOM about two weeks ago to immediately redesign the arms to avoid any further delays.

“We do not want to wait a few months to finish an analysis, only then to learn that we need a Plan B,” Robbins told members of the rail authority board of directors Monday.

Robbins said in an interview he expects there will be disagreement between AECOM and the contractors who are responsible for fabricating the canopy arms over who is to blame for the cracking problem and any construction delays associated with it. However, the city will not pay any extra cost to resolve the problem, he said.

“I’m not ready to assign blame, but I know it’s not us,” Robbins said. “We’re not ready to sort out blame yet. We still have more analysis to do.”

The arms are designed to support overhead fabric canopies that would extend toward the center of the station platforms to provide travelers with shelter from rain and sun as they wait for trains.

The arms are built in two segments, and the original design called for the upper arm to be constructed out of grade 50 steel that is then galvanized to help protect it from the elements. The lower segments of the arms were constructed out of grade 100 steel, but in some cases the lower arms cracked after they were welded and galvanized.

Contractor Nan Inc., which is building rail stations in East Kapolei and Hoopili, found cracks in one canopy arm in April, but that arm was never erected.

HART also reported that contractor Hawaiian Dredging Construction Co., which is building the three rail stations in Waipahu and Leeward Community College, found four cracked lower canopy arm segments at a Kansas plant that was manufacturing them.

“What we have determined through our expert consultant metallurgist is that the grade 100 steel on the lower arm is more susceptible to cracking, particularly when you put it in a galvanizing bath, which is needed for corrosion protection,” Robbins told the HART board Monday.

An investigation into the cause of the problem is continuing, but “it just does not make sense for us to delay refabrication and installation any longer. We’ll spend more money on (delays) than we will replacing these lower arms,” Robbins told the rail board Monday. He said the upper arms also will be checked to ensure they are sound.

The redesigned lower canopy arms will use grade 50 steel, which will require that they be somewhat larger than was called for in the original design, Robbins said.

The redesign work for the arms being built by Hawaiian Dredging is already complete, and AECOM reported they need about three more weeks to complete the redesign for the arms being built by Nan Inc., Robbins said.

The lower canopy arms will also be redesigned for the three stations between Pearl Highlands and Aloha Stadium, but none of those have been fabricated yet, Robbins said.