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
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