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Freespan Correction

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Subcon provide a standard range of fabric formwork supports for rectifying freespans. Our slab range suits spans with height up to 0.5m (20″). Our pyramid bags support up to 2.7m (108″). Standard pipe diameters range up to 1200mm (47″). Above this height and diameter, we can custom build formworks to suit your specific application. Subcon has provided clients with custom formworks for span heights up to 5 meter.

These formworks are manufactured inhouse and are kept in stock at each of our international offices.

For high current applications we have developed heavy density grouts with density over 3.5T/m3. These provide ultimate stability in high current applications up to 7m/s. Read about our more about our heavy density solution for Wheatstone and learn how we were able to pump this grout 250m from a vessel.

For freespan corrections on escarpments and submarine cliffs, read about our Turksteam pipeline grouted supports on a 30 degree slope.

FAQ’s

Critical pipeline freespans can form when:
a) a pipeline spans between two hard ridges on the sea floor;
b) a pipeline scours underneath forming a span;
c) scouring occurs at the touch down points either sides of crossings and buckle initiators

Freespans are important to rectify due to fatigue induced from vortex induced vibrations and to prevent buckling due to cyclic loading.

The best way to rectify a freespan is to support it with a grout inflated formwork. The formwork provides a mid span support, changing the natural frequency of the span’s response to vortex induced vibrations.
Fabric formworks can also build weight bearing supports for pipeline spans that may be overloaded during operational cycles. Spot rock dumping and frond matresses can also be used to rectify spans in some applications.

Freespan interventions are not a depth limited operation, however the time taken to deploy supports increases with water depth. Subcon has installed freespan supports in up to 1000m water depth.

Our proprietary mix designs control for shrinkage, micro cracking and compressive strength. For high current applications where on-bottom stability is a concern, we have developed heavy density grouts with density over 3.5T/m3.

Span rectifications at buckle initiation touch down points are complicated because the pipeline is moving laterally. The best way to rectify these run-away span initiation sites is by installing an X-Matt prior to installation. The touch down supports can be engineered in at an acceptable distance either side of the buckle initiation sleeper.

For situations where the pipeline is already in operation, Subcon can provide solutions using spot rock dumping and fronded mattresses to arrest run away scour at the touch down point .

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Featured Products

Subcon Standard Formwork Subcon Custom Formwork Offshore Bottom Opening Bags

Equipment

SGM1000 SGM2000 20ft Grout Testing Laboratory Offshore Cement Silos Subsea Grouting Turntable

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