Warm up procedure in high temperature service



A pump in high temperature service requires gradual preheating before starting.
Failure to warm up the unit properly prior to its starting may result in distortion,
deformation, or even cracking of the casing, or other parts, due to thermal shock.

A pump in high temperature service also requires hot-alignment to adjust for  
thermal growth. Operating a unit before it reaches, or is close to, its operating
temperature may cause rotor or bearing misalignment, excessive thrust load, or
high nozzle load.

The following definitions are used for the purpose of this discussion:

  • Operating temperature - the actual temperature of the pumped liquid.

  • Hot alignment  - an alignment made when the casing temperature is
    within [ * ] degrees Fahrenheit of the operating temperature in a high
    temperature service.

  • High temperature service - a service whereby the operating temperature is
    more than [ * ] degrees Fahrenheit above ambient temperature.       























There are many risk factors involved in high temperature service that make it
necessary to preheat and hot-align a pump carefully:

  • Components with dissimilar materials may have different expansion rates
    due to differences in their coefficients of thermal expansion.

  • Different pump sections may have different thicknesses, supports, or  
    stiffeners, and may expand differently than other sections.

  • The temperature distribution in the pump is uneven. The surface areas in
    direct contact with the pumped liquid (wet areas) is expectedly hotter than
    outer surface areas, or non-wet areas.  

  • Certain pump sections such as the seal chamber (or stuffing box) and
    bearing bracket (or housing) may be provided with cooling systems thus
    making their temperature cooler than in other sections of the pump.

Pump preheating can be done by circulating warm liquid through the casing and
should include the suction and discharge piping in close proximity to the pump.
The amount of warm liquid should be adjusted to obtain a typical warm up rate of  
[ * ]  to [ * ] degrees Fahrenheit per minute. It is OK to use a faster warm up rate for
small or single stage pump and a slower warm up rate for big, multistage, double
barrel, or pump with dissimilar case, barrel, or shaft material. The warm up flow
may vary from [ * ] to [ * ] gallons per minute (GPM) depending on the discharge
nozzle size. For a more effective warming up, it is preferable that the liquid enters
the casing at the bottom and exits from the top, if possible.

Warming up should continue at least until the casing surface temperature is less
than [ * ] degrees Fahrenheit below the operating temperature. Before starting the
pump the rotating element should be checked for looseness by turning the rotor
manually. Check the pump alignment. Adjust the alignment, as needed, to ensure
that it is within the values recommended by the pump vendor.

Extreme caution should be exercised when planning to use a "spare"  or "excess
inventory" pump in high temperature application if the pump were not originally
designed for such use. There are certain design features that must be included in
pumps for high temperature service that are not available in a typical standard
pumps. Some of these design features may include:

  • Centerline-mounting to permit equal, or near equal, upside and downside
    expansion of the casing.

  • High temperature dowelling to permit the axial movement of the casing
    relative to its baseplate.

  • Mechanical seal selected for high temperature service.

  • Cooled, or jacketed, seal chamber or stuffing box

  • Cooled bearing housing or bearing bracket.

  • Downgrade of the maximum allowable working pressure (MAWP) due to
    the lower allowable stress of some casing materials at high temperature.
    Some examples: cast iron and 300 series stainless steels.

It is strongly recommended to consult with the original vendor if a "spare" or
"excess inventory" pump is suitable, or can be modified, for high temperature
service.


R: 0111WAUP
C: operation
F: temp_warm_up


[ * ] Some information are excluded in this Beta version article.
Read more.
CENTRIFUGAL-PUMP.ORG
Related topics

Temperature rise at normal operation
Temperature rise at shut-off operation
Warm-up procedure in high temperature service
Thermal shock
Conversion factors
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