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New Build Power Plants

TWI’s involvement in new build power plants has both achieved optimisation of the design and fabrication phases of the building of the plants, as well as the minimisation of any subsequent issues with the built plants. TWI has undertaken at least four high value projects, with a combined total value of £3/4m. With recent figures indicating that there are up to 250 new conventional fuel (coal, gas and oil) power stations being built globally, TWI understands the importance of ensuring that these plants are able to commence operation as smoothly as possible.

TWI’s expertise provides clients with an array of benefits, such as assurance of the integrity of their plant, confidence in the operability of the assets and an increased safety of the power station in operation. Profit from a financial point of view is also ensured through allowing money to be saved on re-doing work or costly outages, which can amount to £100 million per day for some plants. Alongside this, TWI is able to provide design consultancy from a welding perspective, on-site third party inspection, welding engineering support as well as risk based inspection, among other support.

An instance of TWI’s involvement in a new build power plant can be identified in the successful building of a Combined Cycle Gas Turbine power station. The plant was made up of gas turbines, four heat recovery steam generators (HRSGs) with supplementary firing and steam turbines. There were concerns about the workmanship of the plant including issues regarding the fabrication of the four heat recovery steam generators, the high pressure steam pipes and superheater outlet headers. TWI worked with the EPC contractor to develop an inspection and weld remediation for the affected welded structures.

TWI’s assistance in the CCGT project was divided into two phases. The first phase consisted of an initial scoping, in which TWI requested to carry out a visual examination at the site. This phase lasted one week and all accessible pipe and header welds were inspected, the level of workmanship and weld quality was reviewed – using available light and hand held torches, and portable hardness testing. The acceptability of welds to ASME Section 1 requirements was commented on. The results of this review revealed significant defects, including non-compliance of the P91 welds in HRSGs with ASME Section 1 quality requirements, incomplete welding documentation and low hardness P91. Based on these defects, TWI provided some recommendations, such as full visual and NDE inspection of all four HRSG’s, establishing the effects of PWHT on P91weldments, ensuring qualified weld repair procedures, considering removal of defects by machining and investigating low hardness values found on the P91 pipework. TWI was also requested to provide a fully qualified expert welding engineer to provide four weeks of site support to assist in correcting the identified issues.

The second phase took place six weeks later, during which there was a TWI expert on site. This phase consisted of a hardness - as well as PMI, UT and PAUT, RT and Boroscope - inspection, identification of defects, review implications, advice - and review - on repair qualification and HT/PWHT, recommendation of remedial work and supervision of implementation, advised additional testing – such as creep testing – and liaison with operator, designer, manufacturer and Third Party Inspection agency.

TWI’s recommendations regarding corrective work in the CCGT project guaranteed the removal of many of the initial issues with the plant, through expert guidance of the clients, regarding matters such as further destructive testing of suspect welds and replacing and repairing critical components onsite. The proficiency and independence displayed by TWI is not isolated to this project only, and has resonated throughout other new build power plant schemes that we have been involved in. This confirms TWI’s confidence in holding the ability to provide the appropriate, beneficial knowledge in order to warrant optimal results. It has also highlighted that early support from an independent expert body, such as TWI, can significantly save cost through early stage remedial action.

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