The recovery from the 5 February 2015 steam turbine fire at the Martigues 5 and 6 combined cycle plants in the South of France, and restoration of the site to full health – 18 months later – was the subject of a very interesting presentation by Antoine Pfister and Andrés Sanchez Roa at the UK IMechE’s Steam Turbine and Generator User Group 2017 conference, Birmingham, UK, 22-23 March.

Martigues 5 and 6, each 465 MWe, entered commercial operation in 2012 and 2013, following a repowering project. They each consist of a GE 9FB gas turbine plus an HRSG providing steam to a Rateau- Schneider steam turbine. The two Rateau-Schneider steam turbines were originally used in oil fired units on the site, rated at 250 MW each. For the combined cycle configuration they were slightly modified and output reduced to 165 MW.

The fire, which lasted about one hour, started at around 5.45 am, when unit 6 was in start-up, with the steam turbine generator at a power level of about 70 MW, and unit 5 in slow roll. Information recovered from the unit 6 DCS showed the following sequence of events: HP control valves behave erratically; hydraulic and lube oil pressure variations; rapid decrease in turbine oil pressure, first hydraulic then lube oil (the decrease continuing even when the emergency pumps start running); fire detection system alarm on the HP turbine; steam turbine trip on low lube oil pressure; loss of information from the DCS.

Investigation indicated that the fire had started when mineral oil from the hydraulic control system (which is of the same composition as the lubricating oil and comes from the same main tank) leaked and came into contact with the HP casing of unit 6, which, at more than 300°C, is one of the hottest parts of the machine.

From the unit 6 HP/IP turbine the fire then propagated around the steam turbine and then under it. Unit 6 suffered damage to cables, electrical shelters & junction boxes, instrumentation, piping, supports, condenser, main steam valves, steam turbine, condenser, steam turbine auxiliaries, lube & lift oil piping/skid, generator, excitation system, steam turbine crane, steam turbine enclosure, civil work. Damage to unit 5 was less severe, mainly to cables, instrumentation, insulation and support, while utilities common to both units were also damaged, including electrical rooms, control room, main crane and chemical skids.

Thankfully the main oil tank remained intact due to the fire protection system.

The extensive programme of inspection, repair and renovation (which included complete replacement of the instrumenation & control system and electrical equipment) was described in the IMechE paper.

For the unit 6 steam turbine itself it was found that the insulation gave a good deal of protection from high temperatures and also from thermal shock due to water spray during fire fighting. The bulk of the damage was found to be to steam turbine balance of plant and auxiliaries.

Among the enhanced fire risk mitigation measures implemented were flange modifications installed on the oil pipework close to hot surfaces to contain leaks, as well as improved fire protection provision on steam turbine bearings, in actuator areas and over all oil pipework routes.

It was also found that HVAC systems needed improvement to prevent smoke and ash from entering the control room and electrical rooms.

Fire mitigation lessons have been promulgated to other EDF sites.

Martigues unit 5 was returned to service in quarter 3 of 2015 and unit 6 in summer 2016, and over the 12 months to the end of 2016, the site produced over 3 TWh, the highest production level since 1980.