——— Sample Riser Calculations ———
The R2.X Sections of the Manual offer typical output data sheets for various
types of installations. The program is a single axis analysis and does not
account for significant forces being imposed on the at riser horizontal connection
interfaces. Where doglegs occur in the riser, independent calculations for
the segment below the dogleg and the segment above the dogleg are needed.
Header information on the data sheet includes the expansion coefficient,
the presumed installed or ambient temperature, the max or min pipe operating
temperature and the elevation of the anchor (if present). Also identified
is whether or not there is a static head at the top of this riser and whether
or not water is being supported. These are useful when working with a riser
made up of several smaller segments with expansion connections in between.
The last bit of header information is whether or not the fluid supported is
liquid or gas. If this is a steam pipe, the weight of the steam is ignored
in the calculation.
Shown on the left is typical data indicating the presence of isolators on
the various floors. Floor heights are listed in the "Floor Ht" column with
Elevation relative to the base in the next column. Pipe size in inches is
also listed.
The "Initial Support Load" column is the resultant force generated by the
empty pipe weight at each support location. In effect, if a support were to
generate this much force at this location, the stresses in the pipe would
be minimized.
The column identified as "Hyd Thrust" indicates loads that are introduced
to the riser system at each elevation by hydraulic forces. These could be
either water weight or pressure generated. A positive sign on these forces
indicates that the force is trying to lift the riser while a negative sign
indicates that it is trying to push the riser downward.
The next to columns indicate the combined spring rate of isolators at each
support location and the initial deflection. In the case of restrained spring
isolators, they could be bench set and installed. In the case of non-restrained
isolators, they would need to be adjusted to this in the field.
The "Initial support point force" is the actual support force at each isolator
location in the installed condition (unfilled riser).
At this point the program introduces the temperature variable, allowing the
pipe to expand or contract and then either works off the anchor (if anchored)
or balances the system support loads against weight and hydraulic forces to
determine spring deflections in the operating condition.
This data is presented in the column headed "Oper Sprg Defl or Dis". The
operating deflection of the springs is listed under this heading for floors
with support isolators. At the top and bottom of the riser, the vertical displacement
is indicated. "+" Dimensions indicate downward motion of final spring deflections.
"-" Dimensions indicate upward motion.
The Operating Support Load is listed in the "Oper Supt Pt Load" column. This
would be the actual support force at each support point.
Lastly are four summary columns. The first two indicate the Initial and Operating
force in the pipe (with "+" being tensile and "-" compression). The last two
compute the stress in the pipe resulting from the operating and installation
forces.
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