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Collapse Resistance of Pipes or Casings

Collapse Resistance of Pipes or Casings

– Water Well Casing –

A comparison of typical strengths of casing materials is shown in the table below.

Casing that is subjected to a high enough pressure externally
(or differential pressure) will collapse.
For any given diameter-to-wall thickness ratio,
there is a critical collapse pressure at which the pipe wall will fail.

Differential pressures can arise during formation pressures,
cementing, development, and pumping.
The expected differential pressure in plastic casing will determine the wall thickness.

For PVC-U, the maximum differential pressures that should be allowed
range from 12 kPa per metre head (for an evenly compacted non-clayeyfilled bore annulus)
to 23 kPa per metre head (for bores in swelling clays).

Plastic casing should not be set to a depth in unconsolidated formations
where the maximum potential pressure differential could exceed
the collapse rating of the casing.
The collapse strength of casing will be affected by slotting the casing.

Comparison of strengths of bore casing materials

Screen Shot 2016-08-06 at 2.28.11 pm

NOTE:

(i) FRO higher temperature with special resins.
(ii) The impact strength of steel and stainless steel is so high relative to PVC-U
and to the demands of water well work, that it is generally not a design consideration.

PVC-U temperature derating

Screen Shot 2016-08-06 at 2.28.11 pm

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