Replacing pumped foam proportioning with inductors at a marine terminal
Field notesPetrochemical marine terminalCase study
A fuel berth’s pumped foam proportioning system had corroded piping, frequent pump failures and unreliable proportioning rates. Archer tested the fire pumps on site and used hydraulic calculations to specify foam inductors in its place.
The feasibility study for this retrofit began with a test of the existing fire pumps, because their performance had never been documented well enough to design from.
The site is a marine terminal berth in Singapore used for loading and unloading fuel cargo vessels. Its foam firefighting system discharged film-forming fluoroprotein foam (FFFP), a protein-based concentrate with fluorinated surfactants added so that it forms a film on the fuel surface. The foam was delivered by remote-controlled monitors supplied through a pumped proportioning arrangement, in which a dedicated pump injects foam concentrate into the water stream at a set ratio. The stainless steel piping had corroded, the pumps failed frequently, and the proportioning rates could not be relied on.
Each of those faults added to the maintenance bill, and an unreliable proportioning rate leaves the operator uncertain of the foam that would reach the berth in a fire. The owner asked for a simpler proportioning arrangement with fewer mechanical parts. Foam inductors met that brief on paper, but they only perform within narrow hydraulic limits, and those limits could not be checked against pumps whose output was unknown.
Why inductors needed confirmed pump data
A foam inductor is a venturi device: water passing through a constriction creates a low-pressure zone that draws concentrate into the stream. It has no moving parts, which is why it suited the brief. It is also sensitive to the inlet pressure and flow it receives, and it imposes a large pressure drop on the line downstream.
At this berth the monitors are mounted at height, so the pressure left after the inductor had to be enough to lift the foam solution to them and still operate the monitors. With the fire pump performance poorly documented, there was no reliable basis for sizing the inductors or for confirming that the monitors would be adequately supplied.
Establishing the hydraulic basis
- Pump testing. The existing fire pumps were performance tested on site to establish what they actually deliver.
- Hydraulic calculations. The measured pump data was used to calculate the pressures at the key riser points where inductors could be placed.
- Specification. Inductor specifications were written so that the manufacturer’s calibration matched the confirmed hydraulic data.
For engineersWhat the calculations had to account for
Two features of the design drove the calculations. The first is the behaviour of the foam concentrate itself, which is non-Newtonian: its viscosity is not constant but varies with the rate at which it flows, so the concentrate pickup through an inductor cannot be treated as a simple water calculation.
The second is the large pressure drop across the inductor. The calculations had to show that, after this loss, there was sufficient pressure to supply the elevated foam monitors. The inductor locations were chosen on the same basis.
The retrofit arrangement
The new arrangement removed the foam pumps and much of the corrosion-prone pipework that had been the source of the faults. Foam inductors, located at points selected from the hydraulic calculations, now proportion the concentrate, with fewer mechanical components between the water supply and the monitors.
Foam inductors placed on confirmed hydraulic data gave accurate proportioning with fewer mechanical components.
Archer (S) Pte Ltd
Reliability and maintenance after the change
Removing the pumps and shortening the pipe runs cut the number of components that can fail or need servicing. The change brought immediate savings in operating cost, together with long-term reductions in maintenance expenses.
Testing the pumps first gave the design a measured hydraulic basis. The arrangement implemented on that basis proportions the foam with inductors in place of the pumped system that had been failing.
