By: Tom Reid, Vice President of Power Generation, ENTRUST Solutions Group
The accidental introduction of water in any part of a steam turbine can cause serious damage, requiring extended outages to make costly repairs. A proliferation of such incidents in the electric power generation industry prompted the American Society of Mechanical Engineers (ASME) Standards Committee to develop a uniform set of design criteria to alleviate the problem.
With updates of ASME Turbine Water Induction Protection (TWIP) standards and the continued focus on fossil plant reliability, TWIP system upgrades have gained increased focus as capital improvement projects.
ENTRUST has identified many clients that have experienced major water induction turbine outages resulting in millions of dollars of damage.
In the extreme case, full blade replacements and rotor straightening technologies have been employed to return the unit to service. Forced outage durations can extend to six months or greater.
The photo in Figure 1 was taken after an LP heater level control failure on a 1960s vintage General Electric LP rotor design. Extensive LP blade damage resulted in full last stage blade replacements.
In more severe water induction incidents, turbine rotors have been permanently bowed. Repairs in these cases could be as extreme as full rotor replacement or a combination of weld repair or heat treatment of the bow.
There are many sources of water induction in steam turbines. The following is a list of the most common sources addressed in the ASME TDP-1 standard:
Generating units that were designed and built before the development of the design criteria are consequently at risk.
A checklist is used to properly assess the status of steam cycle piping systems with regard to the current design criteria. Plant and engineering personnel familiar with the plant configuration can complete input for the program. The analysis then compares plant equipment to the ASME standards and identifies where additional protection schemes are required.
The resulting vibratory response of the blade to this harmonic excitation will dictate whether one or more of the blade’s natural frequencies must be tuned away from the harmonics of running speed. For blade modes that cannot be tuned, keeping the resulting vibratory stresses below the endurance limit of the respective materials is necessary.
It is crucial to recognize the loss of blade material from erosion or other causes, which can significantly alter a blade or group’s vibratory response away from design and perhaps reduce or eliminate margins from multiples of running speed. It is rarely a reasonable course of action to do nothing and leave severe erosion untouched.
Figure 2 shows a silver solder and stellite repair in progress, which was completed by a major U.S. utility. The repair restored the original blade geometry.
Get in touch with ENTRUST’s team of experienced engineers today to learn more about how to best safeguard your turbines from water ingress.
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Tom has spent the entirety of his 15-year career in the power generation industry.
In his current role as Vice President of Power Generation for ENTRUST, Tom oversees a team of approximately 100 engineers, whose expertise covers power plant equipment, modeling, and testing.
Prior to ENTRUST, Tom held turbine design and repair roles at General Electric. Tom is a graduate of GE’s Edison Engineering Development Program and holds 7 U.S. patents. He holds an BSME degree from Virginia Tech, an MSME degree from Georgia Tech, and is a registered professional engineer in the state of Delaware.
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