I am working on a high pressure (280 bar - 4000 psig), high temperature (250 C - 480 F) system and I need a safety device that can vent through a 6" diameter connection. I would love some feedback on viable and practical solutions for this application. I am considering a valve, but I am not sure how practical they are at those pressures, temperatures and size. Any thoughts on that would be great. Thank you for your time.
At this point your requirement description is too general to judge what type of valve you require, ie a SRV (Safety Relief Valve) or a system operated blowdown valve. If it is an SRV then we need to know what type of service ie gas, liquid or steam and whether or not the valve needs to be an ASME certified SRV ie Section VIII gas or liquid service, Section I power steam or boiler service or some other code requirement.
For an SRV a design relieving capacity in CFM, SCFM or GPM is required as a part of the valve sizing determination. In this respect, it would also be good to know why you are spcifying a 6" connection size and whether this is an inlet or outlet size. The first step in determining the correct SRV for a service condition is to select a valve orifice size that meets the discharge capacity required. This selection then determines the required minimum size of the valve's inlet and outlet piping. Generally, the level of pressure and temperature required are inversely proportional to the size of SRV that can be provided; but, if the required venting capacity is low enough then a smaller size valve can be installed by using a concentric pipe reducer between the larger inlet pipe and the required smaller valve connection point. In some high pressure/temperature applications it is actually necessary to utilize multiple parallel SRV's mounted on a manifold to match the capacity requirements with the maximum available SRV size available at those conditions.
On the other hand, if you are looking for some type system operated blowdown valve then potentially a power operated metal seated ball valve, for which a wider range of valve sizes may be available, may meet your needs; but, even in this case the first step has to be to determine the gas, steam or liquid minimum dicharge flow rate, which, will establish the best size for the valve to be used.