* Datteln 4 could start later than Q4 2018
* Project has so far cost 1.2 bln euros
* Plant’s initial opening was planned for 2011 (Recasts with more details on Datteln 4, shares)
By Christoph Steitz and Tom Käckenhoff
DUESSELDORF, March 8 (Reuters) - German energy group Uniper on Thursday warned of further delays to the start-up of its hard-coal power plant Datteln 4, citing damage to a boiler supplied by a joint venture of Mitsubishi Heavy Industries and Hitachi.
One of the last new coal-fired sites to be built in Germany, Datteln 4 has been a major headache for Uniper, suffering several delays and swallowing 1.2 billion euros ($1.5 billion) in investment so far.
Uniper said the 1 gigawatt plant in western Germany would not start commercial operations before the fourth quarter of 2018 and that further delays could not be ruled out, having only just pushed back the start date in December.
The project goes back to 2009 and was originally scheduled to open in 2011.
The most recent delays are mainly due to the plant’s boiler, which was damaged during component tests and took longer than expected to investigate, Uniper said.
“And that’s not a small job, since the boiler has 350,000 welding seams. Of the welding seams that were particularly affected, no fewer than 35,000 need to be inspected individually,” Uniper Chief Executive Klaus Schaefer said.
He said the investigation was conducted in consultation with the boiler’s supplier, a unit of Mitsubishi Hitachi Power Systems, which is a 65-35 joint venture between Japan’s Mitsubishi Heavy Industries and Hitachi.
Uniper, which was spun off from German energy group E.ON in 2016, said that it would have to spend a further low triple-digit million euro sum to get the plant ready.
Shares in Uniper were 0.6 percent lower at 1209 GMT and were among the biggest decliners in the STOXX Europe 600 Utilities Index, which was up 1 percent.
Uniper last year filed a lawsuit against rival RWE for cancelling a contract to buy power from Datteln 4 after continued delays and a significant decline in wholesale power prices over the past decade.
Uniper, in which Finland’s Fortum agreed to take a 47 percent stake last month, said there was a risk that all investments made into Datteln 4 will have to be written off if a new development plan was declared invalid.
The group’s also published full-year results that showed an 18 percent decline in operating profit to 1.11 billion euros, slightly lower than the 1.16 billion average forecast in a Reuters poll, citing a weaker gas optimisation business. ($1 = 0.8076 euros) (Additional reporting by Vera Eckert; Editing by David Goodman, Douglas Busvine and Jane Merriman)