Page 382 - Compression Machinery for Oil and Gas
P. 382

Drivers Chapter  7 363


















             FIG. 7.50 Trip valve.



                                                Continuous         Startup
                Conductivity -
                Micromhs/cm at 25°C
                         Drum                       0.3              1.0
                         Once through               0.2              0.5
                         (ppb, max.)                 20              50
                SiO
                   2
                         (ppb, max.)                 20              50
                Fe
                                                                     10
                Cu       (ppb, max.)                  3
                         (ppb, max.)
                Na + K
                         up to 800 psig              20              20
                         801–1450 psig               10              10
                         1451–2400 psig               5               5
                         over 2400 psig               3               3
                CL       (ppb, max.)                 10           10–30
             FIG. 7.51 Steam purity guideline example.
             interest that are typically monitored, recorded, and trended in order to track reli-
             ability and predict issues with operation, and plan for future outages. A term
             called mean time between failure (MTBF) is a metric that is analyzed for each
             piece of rotating equipment to maximize run times and minimize the cost of
             outages.
                The main points of start-up center around the warm-up of the casing and
             rotor. Condensate must be drained from the casing during warmup such that
             drains are free of liquid. This is an indicator that casing is warm enough to pro-
             ceed to next step in start-up. On HP and temperature units, casing differential
             thermocouples are supplied so operations have an indicator that casing is heat
             soaked (Fig. 7.52). For example, a typical acceptable differential temperature
             between deep and shallow thermocouples is on the order of 82°C. Higher values
             indicate outside of casing temperature is too far from inner casing wall temper-
             ature and more heat soaking is needed before proceeding to next start-up step.
   377   378   379   380   381   382   383   384   385   386   387