Heat Treatment Services - Hydroelectric

Challenge

Stork Cooperheat constructed three large bifurcations as part of the last phase of the Cortes - La Muela Hydroelectric Power Plant. Each bifurcation required post weld heat treatment (PWHT) in order to provide the required mechanical properties. It was necessary to perform the PWHT in-situ- 1km underground; this was especially challenging because of the need for forced cooling of each of fabrication.

Solution

Stork Cooperheat proposed a long established technique using a four-bank channel element unit supported on temporary steel framework. Additional Stork Cooperheat ceramic pad heaters were used on the sickle plate (internal and external) for additional support heating and to compensate for external heat losses. The solution for this resulted in a total of 97 control zones, with overall heater system. Stork Cooperheat attached a total of 111 thermocouples to the bifurcation, using the capacitance discharge technique.

The connection of the required thermocouples and control zones cabling was a significant logistical exercise, with 3500m of heater supply cabling and thermocouple cabling being installed. All thermocouples were recorded efficiently using three Eurotherm paperless recorders. In order to facilitate live monitoring of temperatures and differentials, all three recorders were connected to a laptop that was configured to provide a live overview of all temperatures, heating rates and differentials which greatly improved the monitoring process for both Stork Cooperheat and the client.

Benefits

Stork Cooperheat heat treatments achieved the desired initial heating rates of 25C/hr. As soak temperature was approached, Stork Cooperheat personnel reduced heating rates gradually, in order to ensure maximum control and required tolerance during soak. All three of the heat treatments were completed successfully; an achievement that was due to the level of planning, engineering expertise and the years of experience that Stork Cooperheat engineers and technicians were able to draw upon.

Location	Cortes - La Muela, France
When	2013
Challenges	Location – in-situ, in a tunnel, approx. 1km from the tunnel entrance; creating significant space constraints for the equipment Forced cooling requirements of minimum 25C/hr, including the sickle plate. Forced ventilation to remove hot exhaust cooling air from the working area. Soak temperature tolerance requirement of +/-5C
Largest Bifurcation nominal dimensions:	Diameter: 5450mm Length: 18000mm Max shell thickness: 88mm Sickle plate thickness: 180mm