Posted by David Sear
Just how dangerous can a mussel or even a small piece of drift-wood be to the offshore industry?
Well, if debris is sucked up in the cooling water on an oil rig, then it could cause serious problems in the heat exchanger and possibly lead to a loss of production.
That is obviously a scenario to be avoided at all costs and explains why filters are typically installed on seawater intake lines.
So far so good, but a disadvantage with manual filters is the need for regular cleaning and maintenance.
An alternative therefore being embraced by many operators is to use more sophisticated filters that can self-clean using back-flushing.
That set me thinking: seawater means high chloride content means that sophisticated materials may well be required.
Looking for some answers I was fortunate to meet up with Mr Harald Barth, who is the Senior Sales Manager Process Filtration with German company FAUDI GmbH.
“Your assumption is correction: seawater filters do have some special requirements as to the materials of construction,” started Mr Barth.
“The filter vessel itself tends to be made of carbon steel which is lined with rubber or glass flake. The wetted internals however are normally made of duplex, super duplex or even a material like Monel.”
Interestingly, the intended platform location also has to be taken into account, notes Mr Barth.
“In the seas around Malaysia, for example, the water temperature is higher than offshore China. This means the seawater is even more aggressive, so a higher alloy grade is required.”
Ultimately, the decision as to which material is to be used is taken by the engineering contractor.
In some occasions, indicates Mr Barth, they can even specify the entire filter be made of duplex.
Know-how items
Depending on project activity, FAUDI normally works on eight to fifteen filters each year.
The company first designs and engineers the filter before sub-contracting the actual vessel itself.
However, all of the ‘know-how’ items, such as the wetted internals, are made in-house.
These include parts such as the cartridges, plates, back flush mechanism, rotation device, etc.
Continued Mr Barth: “to fabricate the internals we buy in plates, sheets, tubes, wire mesh and wedge wire. Typically we need about one to two tons of material for the internals of a typical filter.
He concluded: “the number of CRA stockists in Germany is declining, but we can normally obtain the materials we need from within Europe.”
