LITRE METER FLOWMETERS at 2013 Subsea Tieback Forum

Litre Meter will be attending again this year after an initial foray in 2006 when it was in Galveston. Subsea metering is a key area for the Litre Meter team. The VFF rotary piston flow meter has been considerably improved since then with added flexibility in a number of key areas. Experience has been added with thousands more units in service in chemical injection and hydraulic monitoring both topsides and subsea.

The following key areas reflect the six degrees of customisation that have been the tenets of Litre Meters engineering skills.

  • Low flow
  • Subsea
  • Custom connection
  • Custom size
  • High pressure
  • Communications

Low flow. Back in 2006 the VFF LF15 had just been released with typical minimums of 0.2 l/hr on 10cSt. Being a positive displacement flowmeter the higher the viscosity the lower the flow achievable. Various developments have led to the introduction of the smaller LF05. The LF05 has achieved a staggering minimum of 0.04 l/hr at 2 cSt, now installed in the GoM. The LF03 is showing further promise and will be released towards the end of 2013.

Custom connection type. Soon after Galveston we carried out a major subsea project for a Houston based contractor. The spec was 760bar, 4 to 180 l/hr on a subsea hydraulic fluid with 345bar external. Each aspect of the flowmeter was modified to suit the client’s exacting requirements with only the rotor and sensor being left as standard. The fluid connection was a complex manifold design.
Packaging has varied from the simple to the radical. It has encompassed custom manifolds for tight integration, Autoclave connections to the supply of key elements for the customer to package in their own manifold.

Custom connection size. The flexibility of the VFF design when it comes to sizing is best illustrated by an application for chemical injection in Russia. The flow rates were very low, just 25 litres per hour maximum. The modular chamber was installed on 2″ ANSI2500 RTJ flanges providing a complete solution without resorting to any reducers or adaptors. This unit has been re-ordered several times with the latest measuring down to 0.1 litres per hour through a 1″ line.

High Pressure. At the same time we drove our development forward to isolate the measuring element from the pressure vessel purpose of the VFF. This allowed optimised materials for the rotor and chamber – to give better flow range, for example, and simultaneously enabled the use of more exotic materials for the pressure vessel. Many more units have been constructed in duplex and super duplex which would have proved almost impossible to use for measurement surfaces (due to the tolerances of manufacture). The ultimate version of this was a meter for 2,500 bar where the pressure vessel was predominantly 17-4PH stainless.

When Litre Meter separated the meter into two functions of measurement and pressure containment the use of coatings could be exploited. After careful selection and testing most of the VFF range are usually supplied with PVD coating. This remarkable addition enables both higher and lower flow rates. For example, and it is the best example, the HF66 size is rated to 66 l/min maximum. Typically, without coating, the stainless steel rotor could measure down to 5 l/min on water. With a coating the coefficient of friction is reduced and the minimum reduces to 12 l/hr and the added hardness enables over-range up to 130 l/min – subject to factory approval.

Subsea. The number of projects successfully deployed has dramatically increased as well. The VFF is now the meter of choice for one major engineering house at low flows. They have been able to perform in-situ testing, long-term reliability and particle tests. The LF15 has proved to be the heart of their system for chemical injection control in hundreds of installations. One-off projects, at the other end of the scale, have always been challenging but been successful.

Communications. Since 2006 everything from the simplest pulse output to fully customised bus systems and now CANopen has been utilised. They are fully tested for subsea duty with a variety of connector types including O’Brien, Seacon, custom pass-throughs and Tronic.

Come and ask us, give us some parameters and we’ll quickly be able to define a solution. Flow rates from 0.01 l/hour to 16,000 l/hr. Pressures to 2,500bar internal and 500 bar external. Materials range from stainless steel and duplex to titanium and outputs from pulse to CANopen.


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