NRV required on package boiler steam header?

[ProjectEng]

We have a package boiler that feeds saturated steam into a common header that goes to process. There are two manual block valves right off the steam drum, but no non-return valves. There is a coal-fired boiler that also feeds into this header via a turbine. There is a control valve (with appropriate desuperheating valves that allows high pressure steam from the coal-fired unit to bypass the turbine to keep the header pressure steady.

Question: According to code, are we required to have an NRV between the steam drum of the package boiler and the 2 manual block valves?