The Fire Pump Co.

Q: What is the best material to use for column pipe in warm (70°F and above) seawater?

A: It is universally accepted that a chemical composition of nickel, aluminum, bronze equal to ASTM 148B Ca 958 has superior corrosion resistance in seawater. When combined with its natural resistance to the accumulation of biomass, (no hypochlorite injection required) it is an easy choice.

Q: Why limit N.A.Brz to warm seawater?

A: That was not the intent. N.A.Brz is at least equal to or superior to Ferrilium, Duplex SS, 316 SS, type 2 Ni-resist or any of the cold water (North Sea) popular materials when compared mechanically or for corrosion resistance. Up untill now, (before the availability of Badenoch Bronze) these materials were less expensive than N.A.Brz. For example: the Navies ot the world use N.A.Brz exclusively.

Q: If that is true, why isn't N.A. Brz more universally used?

A: That's easy! COST. A lot of the platform projects we work on do not expect to be in service beyond five years. It is difficult therefore to convince the owners, let alone the engineering company responsible for limiting the capital expenditure of the platform, to budget the use of N.A.Brz. However based on the amount of column pipe service we are aware of, through our various service technician contractors, N.A.Brz might be more cost effective than is realized. The additional cost for the Fire Pump Co's Badenoch Bronze will pay for itself twice over the first time the pump is pulled.

Q: What is Badenoch Bronze?

A: Simply put, it is a fabricated N.A.Brz. Column pipe that is considerably more economical to produce than cast Ca 958. This column pipe when used with Ca 958 bearing retainers, rubber bearing inserts, 316 SS shaft, couplings, and bolting is very competitive to baked on phenolic epoxy coated carbon steel or fiberglass. If 500 Monel lineshaft with 400 Monel couplings and bolting are planned to be used with the carbon steel or fiberglass, then the overall cost addition to the whole package is even less significant.

Badenoch bronze is also more economical than 316 SS column pipe. That is especially true when the cost and corrosive effect of Hypochlorite injection (to reduce Biomass accumulation) is factored into the equation. See the Badenoch Bronze detailed properties Bulletin.

Q: Why does FPCo object to the use of column pipe centralizers?

A: The design intent of a vertical turbine pump is that the impellers hang (like a plumb bob on a string) on the lineshaft. It should, when at rest and at full speed, never touch the fluted rubber bearings. The purpose the lineshaft bearings serve is to stabilize the shaft during startup. As an example; if you spin the plumb bob on the string you will note the string will knot-up. The same thing happens to the lineshaft when starting torque is applied, the shaft distorts. The bearings are there to minimize the distortion. The shaft straightens out when it reaches operating speed (Un-winds) and thrust load is applied.

With that in mind, no side load should be exerted on the column pipe that might cause the bearings to bind or attempt to bend the lineshaft. If the lineshaft is so affected the pump will vibrate, or wear out the bearings causing the lineshaft to fail, or break the quill (hollow) shaft in the driver or cause the bearings in the driver to fail.

When you consider that the FPCo service technicians have never seen a straight casing for a purnp to be installed on an oil production platform, it is easy to understand why we do not recommend centralizers.

Q: Why do you object to the use of fiberglass column pipe?

A: Fiberglass column pipe has virtually no lateral dynamic strength. That is why the manufactures require centralizers every 6M (20'). The centralizers then force the pump to bend to the contour of the casing (there is no such thing as a straight caisson) causing the pump to vibrate because the lineshaft is not allowed to hang straight. There are a number of installations around the world where this scenario has been played out. In some cases the solution was to stiffen the pump discharge head or counter balance the frequencies to mask the problem.

Q: How do cold ambient air temperatures impact the pneumatic control and operating systems?

A: The NFPA-20 code prescribes that the machine be maintained in an atmosphere of at least 40°F. Atmospheric temperatures below this level require a heated enclosure, or other means, to prevent malfunctions due to the cold. The engine is equipped with a jacket water heater, the salt-water pumpage is unlikely to freeze, the fuel tank must be heat traced, and air does not freeze if it is dry. Assuming there is not a heated enclosure, cold temperature impacts the pneumatic control and operating systems in the following manner:

1) Saturated utility air will freeze up all the components in the engine starting system. Instrument air @ -40°C dew point (minimum required air supply for the controller) should be used exclusively. Minus 60°C will virtually eliminate any problem.

2) Saturated air (which cannot be used in the controller under any circurnstances) requires that all of the equipment in contact with the starting air system be heat traced. This includes the vessel, the piping to the start system, the regulator, start valve and starter. Heat tracing is expensive and active in order to provide the desired result and therefore is not recommended. "Instrument air only" by comparison is inexpensive and passive.

3) NFPA-20 requires the start system vessel to have sufficient capacity to crank the engine for 180 seconds @ 40°F (4.45°C) without make-up. As the temperature drops below 40°F the effective vessel capacity is being reduced exponentially. Continuous cranking will reduce the reclaimable cranking energy by considerably more.

The FPCo system is designed to operate in temperatures below 40°F and still provide the cranking capacity required by the code plus an additional safety margin. Empirical tests have demonstrated that the design criterions used have a safety factor of approximately 1.33 @ 40°F.

Q: How do cold ambient air temperatures impact an alternate medium like methane gas when used for control and operating?

A: First the Methane gas alternate starting media must be dry (7-lb/mcf) pipeline quality. Essentially the only difference is the .843 specific gravity of the gas would effect (reduce) all the capacities and all the major vents would have to be connected to a flare stack. Heat tracing is dependent on the severity of the cold and the dryness of the gas.