Protection of the pipe during and after pipeline construction is of paramount importance for safety and pipeline integrity. Areas of rock and stone are often encountered during construction of new pipelines. Even with modern pipeline coatings, additional protection for the pipe is necessary where rock or stone exposure is significant.
Historically, additional pipe protection used in these types of situations is achieved through adding either a significant layer of sand or select backfill above and below the pipeline (sand padding) and/or by attaching a high-impact resistant, poly-type rock shield around the pipeline during the pipeline installation process.
To accommodate sand padding, some form of intermittent support of the pipeline is generally required to elevate the pipeline off the trench bottom. Similar intermittent support is also recommended practice when using poly-type rock shields to keep the pipeline from fully resting on trench rocks.
Current methods of in-trench support involve sand piles, sand bags, spray foam and individually formed foam pillows — each with drawbacks:
i) Sand Piles are difficult to install and often oval or dent the pipe when improperly placed.
ii) Sand bags require hand placement for proper support. In open trenches, this can be time consuming and unsafe. Improper placement can cause the pipe to oval or dent.
iii) Spray-in foam is considered to be an obstruction of cathodic protection currents. Newly constructed pipelines full of hydrostatic test water and one metre cover can cause foam to compress excessively.
iv) Foam pillows are light and easily placed — but can float out of position and compress or crack under heavy loads. As with all foam, cathodic shielding is always a concern.
A new, engineered method of in-trench pipeline support is now available — the Structured Pipeline Pillow (SPP).
SPP’s are injection molded and made from high strength, environmentally inert polypropylene or polyethylene resins. Designed to support any size pipeline, SPP’s are most effective with larger diameter, heavier pipelines. One SPP is engineered to carry a single 40′ joint of heavy wall pipeline filled with hydrostatic test water.
Compared with current methods, SPP’s:
i) Stack tightly for transport.
ii) Are light enough for installation from outside the trench and resist floatation when ground water is present.
iii) Help ensure the pipeline is centered in the trench during the pipeline installation.
iv) Maintain long-term pipe clearance above rocky trench bottoms.
v) Ovality and denting concerns are reduced.
vi) Allow cathodic protection an easy path to the pipeline.
vii) Will never biodegrade.
In their extended stacking mode, SPP’s tested well as an effective alternative to wooden skids for many situations such as pipe stockpiling; stringing along the rights-of-way (ROW); and even for some low level skidding during the welding process.
Shielded Metal Arc and Thermite Welding Effect to Residual Stress, Hardness and Crack of R54-Rail Weld Joint