Piping expansion loops

Thermal Expansion in Flare Header - Sliding-type expansion joints may be used in flare headers as an alternative to piping expansion loops, if required to achieve a reduction in pressure drop or where expansion bends may result in liquid surging, subject to the following conditions ... 

Figure 7-35. Pipe expansion loop program. Note Subroutines not included in the program listing. Solve step-by-step using the manual method described, using the functions duplicated as comment statements in the mainline program listing. The comment statements reveal all the basic thought and method.

Shull, W.W. Bogel, G.N. A Simplified Computer Program for Pipe Expansion Loop Design. Hydrocarbon Processing, September 1967, p. 183. 

Multielevation piperacks are usually needed to handle all the required services for piping, electrical, utilities, and instmmentation. The two-level rack is one of the most common but three-level ones are also used. The utility lines are usually mn in the upper level and the process lines in the lower levels. The larger-diameter lines are located to the outside of the rack to be closest to the column supports. Access platforms are required at the battery limit to provide operators access to the block valves and blinds. If long mns of hot pipe are required, a portion of the pipe rack needs to be dedicated to an expansion loop. A horizontal space in the piperack is provided for a set of lines to be flat-turned into a set of expansion loops with the large pipes located on the outside. AH of the pipe turns are in the same horizontal plane, which is an exception to normal piping practice. A flat turn takes up and blocks space for other pipes. Flat turns are generally only made from the outside of the rack to minimize this blockage. 

Tolerance Whenever possible, equipment should tolerate poor installation or operation without failure. Expansion loops in pipework are more tolerant of poor installation than bellows are. Fixed pipes, or articulated arms, if rlexibihty is necessary, are fiiendher than noses. For most apphcations, metal is friendlier than glass or plastic. 

Flexibility is incorporated into piping systems to absorb the thermal expansion. A piping system will have a certain amount of flexibility due to the bends and loops required by the layout. If necessary, expansion loops, bellows and other special expansion devices can be used to take up expansion. 

If unbalanced layouts cannot be avoided, appropriate analytical methods must be apphed to assure adequate flexibility. If the designer determines that a piping system does not have adequate inherent flexibility, additional flexibility may be provided by adding bends, loops, offsets, swivel joints, corrugated pipe, expansion joints of the bellows or slip-joint type, or other devices. Suitable anchoring must be provided. 

Thermal expansion and the resultant pipe stresses must be considered in any piping system design. For example, if the temperature changes from 50 to 600°F, the increase in length would be 4.9 in. per 100 ft for steel pipe and 7.3 in. per 100 ft for brass pipe. This amount of thermal expansion could easily cause a pipe or wall to buckle if the pipe were fastened firmly at each end with no allowances for expansion. The necessary flexibility for the piping system can be provided by the use of expansion loops, changes in direction, bellows joints, slip joints, and other devices. 

As shown in Figure 7-41b, it is doubtful that the piping configuration can be extended enough to allow for proper flexibility without exceeding b if we take the expansion loop off the long side. Therefore, the short side is more desirable. 

Figure 7-54. Important points in this typical line position arrangement of yard piping are heavy lines over columns, utility lines near the center, and horizontal expansion loops with hot lines on the outside of the loops.

Standard and special dimensions and designs to be employed, for example for clearance under walkways, arrangement of expansion loops, installation of insulation, and pipe supports. Special process requirements must be considered in this context, for instance if there is a need for avoidance of pockets of stagnating process material, and consequent orientation of branch connections, etc., or piping that is rapidly demountable for cleaning. 

Wlien expansion loops are required between pumps, it Is necessary to panially run the lines over the pump and driver. Every effort must be made to minimi/e maintenance ob.struak>as by running the piping either outside the area direcily twer the pumps, or at a high enough elevation to jicrmit the removal of the pump t>r driver. 

Determine the amount of expansion in each leg of the loop perpendicular to the diiection of pipe expansion ... 

Expansion loop Piping thermally expands as it gets hot. Allowance must be made for the growth in pipe length, otherwise the pipe will break by cracking at its welds. We burned down a fractionator at the Good Hope Refinery because of such an omission. 

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