Lowering a welded pipe string into a trench with side booms combines a heavy, flexible load with machines working close to an excavation edge. Three numbers drive the plan: how much the string weighs, how far out each machine has to reach, and what its chart allows at that reach.
Pipe weight
For steel pipe, weight per metre is w = π × (D − t) × t × ρ, with D the outside diameter, t the wall thickness and ρ the density of steel (about 7,850 kg/m³). Add coating and concrete weight where present. The load on each machine depends on how many machines share the string and on their spacing.
Work radius from the trench
Pipelayer charts measure the hook radius from the outside edge of the track nearest the load, which is the tipping line. A common planning approach takes the radius as half the trench top width plus a set-back from the trench edge, where the set-back is a multiple of trench depth: about 1.5 × depth in firm, stable ground and 2.0 × depth where the trench walls are unstable. Keep the machine back far enough that its track load does not collapse the trench wall.
Tipping capacity and duty limit
Pipelayer manufacturers publish lift capacity at tipping (ISO 8813). The working load must be held to a fraction of that figure; the side boom planner applies 85 % of the tipping capacity as its duty limit, the ASME B30.14 convention. Never apply a second reduction to a chart that has already been derated, and never extrapolate beyond the end of a chart.
On site
- Confirm ground conditions along the right of way, not just at one point.
- Keep the counterweight extended as the chart assumes.
- Coordinate all machines from one signaller; lower in steps.
The side boom lift planner covers about 210 pipe sizes and 67 machine and boom combinations, and checks load, radius, spacing and the duty limit for each machine on the string.
General guidance only. It does not replace the manufacturer's data, the applicable standards or the judgement of a competent person.