6 | Baker Hughes
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Material Break Point
As previously mentioned, temperature reduction does
not occur immediately at the outlet of the SteamForm.
Spray water injected into the steam must first heat-up to
the saturation point, and then evaporate into steam for
cooling. This phase change is shown in Figure 4. The
SteamForm valve can be used as a material breakpoint
provided the lower grade material is designed to accept
the full upstream temperature.
Heat-up Time, t
1
Evaporation Time, t
2
Temperature = T
water
Temperature = T
saturation
The material break point, in the case where temperature
reduction is a required design factor, is application
specific and is not possible to advice as a rule of thumb
process. The complexity of this calculation stems from
the fact that the evaporation rate is a function of the
following three variables.
• The enthalpy differential between the water and the
saturation point determines the amount of time required,
t1, for heating the water to its saturation point.
• The droplet diameter, which is a function of nozzle
design and injection velocity, influences the amount
of time required, t2, to evaporate the water once it
becomes saturated.
• The length for proper evaporation is determined by
multiplying the steam velocity by the sum of t1 and t2.
Multiple variables are presented in the calculation
and are applied through indirect relationships. For
applications where a temperature reduction must take
place prior to the material downgrade, a Baker Hughes
representative should be contacted to provide the best
location for the material transition.
Figure 4: Evaporation process of a water droplet
Warning:
Steam exiting the SteamForm valve exhibits high temperature. Complete cooling of the steam
temperature does not occur until the spray water evaporates and mixes with the steam. Therefore, the final
outlet set point is not achieved until reaching the factory specified temperature sensor location.
Piping Material Transition
Recommendations
SteamForm valves are often manufactured with high alloy
cast material body such as C12A Grade 91, specially for
steam temperatures exceeding 1000°F. The End Users
typically maximize lower grade material piping at the plant
for cost savings. Lower grade materials cannot withstand
the higher temperatures steam conditions. Therefore,
before transitioning piping material from higher grade to
lower grade at downstream of the SteamForm valves,
specific distance guidelines must be followed. Please
contact factory for evaluation and minimum distance
recommendations.
