To Project Manage the complete evaluation of a Foster Wheeler Steam Boiler. The evaluation was to confirm the plants ability to safely operate at an increased pressure of 750 PSI from the current 250 PSI. The plant was considering adding a Co-generation unit.
The project required both GTT OnSET and third-party personnel to completed, which included the following:
- Opening and Closing of the Boiler
- To facilitate Inspection and cleaning of all pressure components of the boiler including the below:
- Removal and reinstall of internal baffle and boiler components
- Removal of reinstall of insulation on boiler, headers and steam piping
- Acid Cleaning of Boiler
- Pressure washing of boiler
- Complete a full assessment of all pressure components including drums, nozzles, steam lines, generating bank tubes and headers.
Various non-destructive testing techniques were used to evaluate the boiler such as a visual inspection, borescope, Internal Rotary Inspection System (IRIS), In-situ metallography, magnetic particle, ultrasonic thickness measurements to help confirm the integrity of the boiler.
During the visual and borescope inspections we found the generating bank tubes to have a heavy build up internal scale. The scale was so hard to remove that the boiler required to be acid cleanings and high pressure washed twice. A borescope inspection was completed to confirm scale removal from the boiler. Boiler operating efficiency would increase with the removal of the scale.
Scales remaining in tubes after first acid cleaning
Internal View of tubes, after 2nd acid cleaning and pressure washing. Scale remove except for some isolated build-up at bottom bend
After the acid cleaning the generating bank tubes, the tubes were inspected using the Internal Rotary Inspection System (IRIS) IRIS is an ultrasonic inspection technique used to measure wall thicknesses in tubes. The probe is made up of a centering device, an ultrasound transducer and a rotating mirror (turbine). It is performed by immersion in the tubes. An ultrasound pulse is generated by the transducer and guided towards the wall tube through a mirror that is inclined at 45º. The ultrasound reflection (echo)captured are from the inner and outer walls of the tube. The remaining thickness is calculated using the velocity of the inspected material and the difference between the inner and outer echoes. The generating bank tubes were found at or above original wall thickness.
In-situ metallography was performed at four locations within the boiler, including (a) an externally accessed generating bank tube, (b) an internally accessed generating bank tube, (c) the superheater supply tube and (d) the internal steam drum wall above the generating tubes.
These sites were prepared by superficial grinding, polishing to a 1μm polish and then etching using 3%
nital (diluted nitric acid). The prepared regions were replicated using acetate tape and further examined off-site. Optical examination was performed at magnifications up to 1000x.
At the four locations evaluated, no life-limiting degradation was observed. No creep damage/voids or any other life-limiting damage were observed at any of the sites evaluated.
The remaining component drums, tubes, headers and piping were all found free of and defects. Design calculation were completed and the boiler was found capable of operating at 750 PSI.