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[rikakose]

Questions about the steam coils for a storage tank:

 

1. An old chemical storage tank, equipped with steam heating coil. There is only level indication. In principle,  the liquid level in the tank should be higher than the coils. In order not to interrupting the production, operators often ignore the low level alarm and let the coil exposure to gas phase. 

One typical design is that link the level meter and steam flow. But because it is old tank, it costs too much to add new control system. 

Are there any other solutions? Are there some accidents caused by steam coil cracks, that I can show the examples to the operators.

 

2. recently, an very experienced old process engineer pointed out a design requirement which I never paid attention to- the temperature difference between the steam and liquid. The steam temperature can not be too much higher than the boiling point of liquid, because there will be a lot of the bubbles generating on the surface or the coils which shorten the life time of coils. According to my experience in cryogenic equipment max. dT is 200C the normal stainless steel elastic limit. I didn't find any other articles discussing the dT issue. Why the bubbles damage the coils? Same reason to the dry surface?