we have a problem with reading through level gauge on steam drum with 400 C operating temperature and 120 bar pressure. Reason for this is the glass (mica) that is used to read the level because of steam has become blurred, and reading is difficult. Is there any way to fix the problem? I mean a better glass? And standard tell us what for what kind of level we should use in steam drums? if there is any standard, which? And finally is it better to go to magnetic float type level gauge or not?
I don't know what your budget is, but back before I retired (over 9 years ago) our normal practice for boiler drum level measurement was to use differential pressure transmitters (with pressure compensation) for control and indication, with a code required independent measurement for indication and protection. The usual choice for the independent measurement and indication was a Hydrastep transmitter.
There may well be something better available now.
Depending on site location and requisite code requirements, you may have issues with moving to a magnetic instrument on a drum with that high of pressure. For those following ASME Pressure Vessel Code, PG-60.1 delineates what is allowable. Clark-Reliance is one of the better vendors for drum level indication, so having a chat with one of their sales representatives will put you on the right track. Also, there is no way I know to fix a cloudy gauge glass (mica issue).......it needs to be replaced.