What code is the boiler built to? ASME I?
If that is the case, you don't have names like "Safety Operation Pressure". You have Maximum Allowable Working Pressure (or some call it Design Pressure). You can operate as close as you want to this value depending your risk tolerance for spurious pressure relief valves actuation.
10% margin is generally accepted as "safe" from the point of view of avoiding spurious relief events. But this is also dictated by:
- How confident you are about the valves calibration.
- How frequently you calibrate/maintain them.
- How stable your operation is. If the boiler is working at a very steady regime, you may get closer to the MAWP. If the seam demand is fluctuates in short term spans, 10% may not be sufficient.
.- The consequences of an spurious event.