meteng is correct, the codes are design codes and not operating codes, but there are some areas where some areas of concern exist in the operationsof combined cycle plants.
2 areas that come to mind would be covered by B31.1 in the design , but apparently something seems to get lost in the translation.
B31.1 par 102.2.4 allows short term operation above ASME allowable stresses , but usually the time limits defined by ASME are not programmed into the DCS and there is then no time limit imposed on operators for such overpressure. Typically the worst case is overheat of the cold reheat pipe during startup windage heating of the HP turbine- normally this pipe is carbon steel and siche B31.1 does not provide allowable stresses for carbon steel above 750-800f, any overheat above 800 F is technically not permitted. A bigger concern is leakage past the HP bypass which may heat the carbon steel pipe above 800F for prolonged periods- this can lead to graphitization of this pipe.
Another area that sometimes does not seem to meet B31.1 rules is overpressure protection of natural gas lines. If 100% full casualty flow overpresure protection is not provided by relief valves, then B31.1 allows alternate overpressure protection provided several redundant mechanisms are in place , including:
a) 2 independent PRV's in series, both set to limit downstream pressure to bleow design pressure. Independent technially implies independent power supply and control systems- this is sometimes not met
b)downstream pressure switch, hardwired to an inlet stop valve. This inlet stop valve must have an actuator sized to close within 1 second.
c) other items- see the code
