Hi meanstone,
That’s a very good question. I work for an industrial gas company with over about 10,000 cryogenic storage tanks on customer sites around the world. Similarly, all the major industrial gas companies have thousands if not tens of thousands of tanks in inventory.
There is no industry standard for determining boil off (generally referred to as NER). There’s a definition of NER here that may prove useful for discussion:
You may also find patents such as this one for equipment intended to measure NER:
But the bottom line is there is no industry standard on how to measure this.
If you’re working for a tank manufacturing company, it would behoove you to discuss this up front with anyone purchasing a vessel, especially an industrial gas company. I can’t speak for other major industrial gas companies, but our company has a proprietary procedure and test equipment for performing this test. Since the industrial gas companies will specify and want a guarantee on the NER, you will need to make sure you agree to what that means and how to test it, so I’d suggest having this discussion up front with your customer.
There is of course, a methodology behind it that goes back to first principals, specifically the laws of thermodynamics, so one can argue that the definition of NER has a specific, thermodynamic meaning which can be adjusted for various ambient and tank conditions. In fact, we do this, knowing it won’t be sea level and 70 F that the test will be performed at, so we need to adjust to local conditions. The whole thing can get a bit messy if no agreement has been made up front, so I'd strongly advise you to make sure you/your company knows what process will be used if the tank is to be tested.
