ASME TDP-1–2006 pdf download.Recommended Practices for the Prevention of Water Damage to Steam Turbines Used for Electric Power Generation Fossil-Fueled Plants.
1 SCOPE This Standard includes recommended practices con- cerned primarily with the prevention of water damage to steam turbines used for fossil-fuel-fired electric power generation. The practices address damage due to water, wet steam, and steam backflow into a steam turbine. The practices are applicable to conventional steam cycle, combined cycle, and cogeneration plants. The practices cover design, operation, inspection, testing, and mainte- nance of those aspects of the following power plant systems and equipment concerned with preventing the induction of water into steam turbines: (a) motive steam systems (b) steam attemperation systems (c) turbine extraction/admission systems (d) feedwater heaters (e) turbine drain system (f) turbine steam seal system (g) start-up systems (h) condenser steam and water dumps (i) steam generator sources Any connection to the turbine is a potential source of water either by induction from external equipment or by accumulation of condensed steam. The sources treated herein specifically are those found to be most frequently involved in causing damage to turbines. Although water induction into the high and intermediate pressure tur- bines has historically been recognized as the most dam- aging, experience has shown that water induction in low pressure turbines can cause significant damage and should also be taken seriously. 2 CRITERIA 2.1 Basis 2.1.1 The recommended normalpractice to prevent turbine water induction is to (a) identify systems that have a potential to allow water to enter the turbine
2.1.2 However, since malfunctions do occur, one or more of the following steps are recommended to prevent turbine damage due to water induction: (a) detect the presence of water either in the turbine or, preferably, external to the turbine before the water has caused damage (b) isolate the water by manual or, preferably, auto- matic means after it has been detected (c) dispose of the water by either manual or, prefera- bly, automatic means after it has been detected 2.1.3 No single failure of equipment, device, or signal, or loss of electrical power, should result in water or cold steam entering the turbine. 2.1.4 Steam lines connecting to the steam turbine directly or indirectly should be designed to ensure that any saturated steam or condensate that may have col- lected while the line or portion of the line was out of service is drained and warmed adequately prior to being returned to service. 2.1.5 Any automatic control system used to control steam line drain valves identified in these guidelines should be designed so that the system has a means of initiating automatic valve actuation and a separate means of verifying the appropriateness of the automatic action. For example, if a drain valve is closed automati- cally based on a timer, something other than the timer, such as a level switch that would alarm if water were still present in the steam line, should be used to verify that the timer initiation was appropriate. If an inappro- priate action is taken, an alarm should be provided.
2.2 Definitions 2.2.1 General cold steam: as a general rule, defined as steam inducted into the steam turbine with the steam temperature more than 100°F lower than the temperature expected for the operating condition of the turbine, or loss of measurable superheat. Temperature mismatches of more than 100°F may be permissible on a case-by-case basis, if this has already been considered in the design of the turbine. combined cycle: used in this Standard, a hybrid of the gas turbine (Brayton) and steam(Rankine) cycles. Waste heat contained in the gas turbine exhaust is fed through a heat recovery steam generator that produces steam that is expanded through a condensing steam turbine to pro- duce power. conventional steam (Rankine) cycle: steam is produced by heating water in a steam generator and then expanded through a steam turbine to produce power. 2.2.2 Systems admission steam (induction steam): steam admitted to a steam turbine through an extraction/induction opening. During certain operating modes, the same turbine open- ing can supply extraction steam, depending on the pres- sure in the steam line compared to the prevailing steam turbine stage pressure. This dual mode of admission and extraction is termed “dual admission/extraction.” auxiliary steam: a steam system used outside of the main cycle systems for plant uses such as equipment power drives, air heating, building heating, start-up heating, etc. condensate: the main cycle piping system that transports water from the condenser to the deaerator, feedwater system, or steam generator. Heating and purification of the water may be a part of this system.