Padding (or backfilling) machines are designed to protect and cushion pipeline infrastructure by replacing soil of the right composition back into the pipeline ditch. Padding with the correct materials, in addition to applying an appropriate pipe coating, ensures maximum resistance to damage.

Keeping pipe coating, pipe size and soil conditions in mind, contractors can specify the most efficient padding machine for the job, from a pull-behind padder to a completely self-propelled, self-loading machine.

The padding process

When installing a pipeline, top soil is generally set aside for future use, while the subsoil is dug by a trencher or excavator. Subsoil is usually placed onsite in a separate location so that the padding machine conveyor will not interfere with the top soil. A padder is then employed to surround the coated pipe with aggregate material.

The size of the aggregate material is decided upon dependent on the subsoil content. The size of aggregate used to pad the pipe is adjusted by different screen sizes mounted onto the padding bucket or padding machines.

Chipping of the pipe coating can occur if the pipe rests against the ditch wall or the rough bottom of the ditch. Some companies opt to use sandbags to keep the pipeline off the rough bottom of the ditch, but a padding machine can still easily encase above and below the pipeline with small aggregate material. Other companies choose to pad aggregate on the bottom of the ditch before the pipeline is laid, giving it a soft bed. In this situation, another padding machine can follow, covering the sides and top to meet the oil and gas company’s specifications.

Different types of padding equipment

CRC Evans can recommend the correct padding equipment to meet the contractor’s requirements.

A padding bucket affixed to an excavator can be used to pad hard-to-reach areas such as tie-ins.

A pull-behind padding machine can be parked in a stationary position for tie-ins, using an excavator to load and a remote-controlled conveyor unit to distribute aggregate material. Or, it can simply be pulled along the ditch for padding.

For longer and quicker padding jobs, self-propelled, remote-controlled padding units will easily gather material, separate the aggregate, and distribute it using the conveyor system.

The CRC Evans Super Padder is a high-volume padding machine built to handle pipeline diameters of 36 inches and greater. Designed by Laurini, it allows a single operator standing away from the padder to have full control through remote electronics. Having the operator off the machine also has significant safety benefits.

Padding challenges

The challenges of padding are not necessarily dictated by the terrain but by the type of aggregate material. The size of the screen area on the machine and the force of the shaker/screen assembly can make a difference. Another commonly encountered problem of padding machines is that wet clay will clog a screen. Furthermore, the subsoil can be aerated and have a tendency to deteriorate the walls of the ditch. In such a case, the walls would need to be more tapered and the spill pile placed farther from the ditch in order to avoid safety concerns.

When correct backfill procedures are employed by experienced operators using well-designed padding machines, the long-term integrity of the pipeline is greatly enhanced. Problems such as future leaks, expensive re-digs for repair and voids in the subsoil that lower the surface and create erosion over the pipeline can all be prevented with expert pipeline padding.