Exhaust Gas Diffuser 1 Refurbishment

The problem

The GT 26 Exhaust Gas Diffuser is a segmented diffuser consisting of ten independent moving plates.  These form an liner in the exhaust path to the HRSG.  Between the liner plates and the outer casing there is layered insulation matting.  During the operation of the GT26 the EGD 1 liner plates will require repair.  But if not carried out by competent and experienced engineers the repair will lead to further damage.

If the plates are not allowed to move correctly as the EGD1 thermally expands and contracts.  This in turn leads to further and more extensive damage and subsequent erosion, movement and loss of the insulation matting.

The loss of the insulation will cause the outer casing of EGD1 to heat up significantly. This has an impact on the operation of the gas turbine as EGD1 is located inside of the GT Thermal Block.  The heating causes both instrument damage in the thermal block from localised radiating thermal heat.  Eventually  raised thermal block temperatures (with higher ambient temperatures) will lead to the need to de-load the GT. Reducing  the GT exhaust temperature.

Our client was in the position of having to de-load his unit during summer months due to this issue.

The solution

The client approached Salko with his problem and the challenge to provide a proposal for a turnkey solution to his issue. Involving the reverse fabrication of the liner plates from stainless steel flat plate; procurement of the new Arnold layered and reinforced insulation. The complete onsite removal, repairs and installation of insulation and new liner plates.

All of this had to be completed with the window of GT outage, at short notice and at a financial value that would meet the procurement team’s financial criteria.

The outcome

Salko had the team, knowledge and tooling to complete the removal, repairs and installation.  We also had a good partnership with the Arnold insulation team.  Our main challenge was to establish a new partnership with a steel fabricator who could work in complex fabrication of large sections of 8mm and 10mm stainless steel involving rolling, cutting and forming.  Someone who could work quickly as the turnaround time was limited.

We found our fabricator in Sheffield (of course) and we have subsequently established an excellent partnership for this field. With the ability to offer a full turnkey service.

The initial removal of the existing liner plates was carefully executed. Limiting the  damage to the plate as this was then shipped to Sheffield to start the reverse fabrication process. The material specification had already been ascertained and the flat plate stainless steel was procured and waiting.  We embedded a member of the Salko team experienced in Exhaust repairs with the steel fabricator while the main team completed the removal of the remaining plates.

While the fabrication and removal/repairs was being progressed onsite. The insulation team prepared for the removal of the old insulation. The team then installed the new layered and reinforced insulation from Arnold. The insulation contractor was another established partner who is known to Arnold and approved to work with their insulation.

New insulation pins were installed, repairs and replacement of the “T “ supports were completed. Once this was finished the new insulation layering could be installed, starting at the six o’clock position.  The fabrication of the plates was ordered in the reassembly sequence required to ensure that the installation flowed flawlessly.

All the new plates were installed inside of the planned window for the works and the unit handed back to the client.  A full quality pack (including the welding documentation) and a final report were handed over.

On restarting of the unit the client reported a significant drop in the thermal block temperature. This showed a reduction from 73oC to 56oC at baseload (and this at a 12oC lower ambient temperature).   However the excellent news for both our client and the Salko team was that after a summer’s operation there was no requirement to de-load the GT.  This saving was calculated as covering the cost of the refurbishment by Salko.

After the success of the first unit Salko was invited back to complete another EGD1 Refurbishment with the same client.

Get in touch

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