Hugh,I found it under 9/5.5 and 9/5.7 which is what I think you meant, and not chapter 10. I believe the answer to your question is dependent upon what you define as the maximum allowable working pressure (MAWP). In the case of a submersible we might intuitively define MAWP as 1ATM, but the wording of rule 9.5.7.1 does not require that. In the case of a K-350 for example, there's nothing to stop a pilot from pressurizing it to 3ATM and operating it as a semi-ambient vessel. Not realistic of course, but given the language of 9.5.7.1 it would meet ABS standards if you wanted to use a 45psi relief valve.
For practical purposes, I believe you want the relief valve set for 15psi which is the maximum normal operating pressure that most 1ATM subs would strive to achieve. Rules 9.5.7.1 and 9.5.7.2 are poorly worded in my opinion and appear to be drawn from language not originally applicable to human-occupied pressure vessels. You could interpret "normal operating condition" as written in 9.5.7.2 to mean "operating condition" (15psi) or "physical condition" (the sub may be fabricated to sustain a maximum pressure of 300psi). I suspect an inspector would interpret it as operating condition, which really is the only thing that makes sense.
Jon Hugh Fulton wrote:
Hi Jon, ABS 10-5.5 and 5.7 Pressure vessels and hx are not to be located within the pressure boundary ---------unless calcs show that inadvertent release of the contained fluid(s) will not increase the pressure inside the chamber by more than one atmosphere. 8/7.5.2 also. The cracking pressure on some relief valves you would be lucky to have it under 2 psi. But if you had 5 psi then on a hatch with a seal on it OD of 24" would have one ton pushing it open. I am trying to do the holding down with two catches but if the hatch is supposed to take one atmosphere then there is 3 tons to contend with. If you arrive back at the surface with 1 atmosphere and given that the 15 psi is in keeping with oxygen partial pressures limitation, then that could be a fair amount of air to pass out through the relief valve. Regards, Hugh
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