The inlet pr. (SOR) is approx 26 kg/cm2 at convection inlet. At EOR, it becomes approx 30-32 kg/cm2. The inlet pump is designed for 50 kg/cm2 pressure, assuming worst case condition of 3 mm coke deposits in radiatoion tubes – which is never reached. The limiting temp. (as per the original calc which I have seen) has been established by assuming worst combination of pressure & temp. on 7 th tube from outlet (total 34 tubes in a pass) and assuming 22 kg/cm2 pr. in that tube (which is very very high – should have been approx 8-9 kg/cm2, considering outlet pr. -4-4.5 kg/cm2). After that assumption, back -calculation was done to reach the figure of design limit -612 C.
Now, as that design pr. will never be reached, higher op. temp. shoud have been allowed. However, the concerned aquthority is asking for some code/std. or Recomm. Practice reference for changing the op. temp. limits.
‘Hope you can help.