During the startup of the triple-pressure HRSGs, plant staff noticed steam coming from the stack and a discrepancy between feedwater and steam flows. On shutting down the unit a T23 superheater tube was found with a complete circumferential failure. The failed tube was removed and the bore was plugged with some difficulty due to poor access and the uncommon material.
Very large differences in tube wall thinning rates by flow-accelerated corrosion (FAC), or in some cases fluid erosion, are observed in the low-pressure (LP) evaporator tubes of certain HRSG designs. The tubes located near the duct wall and occasionally near the gaps between module bundles have more rapid thinning. Tubes in a given row nominally should have very similar process conditions, both on the gas-side and on the waterside. Different wall thinning rates mean that process conditions differ across the tube row.
As combined cycle gas turbine plants are called upon to play a larger and more flexible role in the generation mix, it’s important to schedule a comprehensive assessment of major components at key intervals to ensure reliable operation.
Waterside Deposits in evaporator tubes have been an issue in steam generators as long as boilers have been used. Substantial experience in deposit formation and management has been gained in conventional goal and oil/gas boilers over time. The role of boiling modes in the steam generator tubes is very critical to areas of deposit formation.
Since 2007, the ASME B31.1 Power Piping Code has included mandatory requirements on the Operation and Maintenance (O&M) of Covered Piping Systems (CPS), previously called High-Energy Piping. The main concern is that the safety of these systems is very dependent on good O&M, which justifies its inclusion in the Construction Code. There is room for flexibility depending on individual circumstances but the responsibility is squarely laid on the Operating Company.
Normal boiler and Heat Recovery Steam Generator Operation have required a complete purge of the boiler by fresh air before startup firing to remove potentially explosive fuels and other substances from the boiler/HRSG. For power plants in daily two-shift cycling (or more frequent starts) this not only adds time to the startup sequence but can impose significant thermal stresses on hot components exposed to cooler purge air.
On the French Riviera, June 10-14, 2019
Partners: TG Advisers, USA; Prof. B Leckner, Chalmers University of Technology
A unique opportunity to update your knowledge on your power plant’s Capital Equipment. Hear from industry-leading experts on Gas Turbines, HRSGs, Fluidised Bed Boilers and Steam Turbines. Sharpen your skills with the latest information on inspecting, analysing and maintaining your critical power generation assets.
Tetra Engineering has partnered with turbine experts TG Advisers Inc., and Fluidised Bed Boiler expert Prof. B. Leckner (Chalmers University of Technology, Sweden) to deliver a comprehensive course set, targeted at O&M engineers with critical technical responsibilities. The programme will run as follows:
Higher demands on outlet steam conditions has led to increased use of modified low alloy materials (9-12% Cr), such as Grade 91. The superior high temperature material properties of these types of steels (strength, fatigue resistance, creep resistance, improved steam oxidation resistance) gives the designer advantages with respect to boiler reliability and thermal performance. The advantages of using this type of materials are many; however, the long-term integrity has been a concern to the industry ever since the first installations.
Tetra Engineering and KED are pleased to announce the release of the Power Plant Simulator & Designer Package (PPSD) Version 19.1. PPSD is a state of the art design and analysis/troubleshooting package for nearly any type of thermal power plant. It includes the capability for both steady state and dynamic simulation and analysis and is developed by KED in Germany.