Exploring the Myth of Flow Metering on Duplex Piping
20 March 2007
Once upon a time an engineer had a requirement to measure the flow of liquid through a pipeline where the flow velocities could be as high as 12m/s and the pressure as much as 100bar g. One of his first thoughts was that this would be an ideal situation to use a clamp-on flowmeter - after all this would remove any pressure issues, avoid needing to make any costly pipe modifications and most importantly not require a shut-down. The problem was that owing to the demanding application and harsh environmental conditions, someone had specified Super-Duplex piping - and obviously ultrasonic flowmeters do not work on Duplex pipes.
So much for fairy tales.
While a rumour has been circulating in the offshore and petrochemical industries that clamp-on flowmeters are not suitable for use on specialised alloys such as Duplex or Super Duplex, the engineers at Katronic Technologies have been installing reliable instruments around the UK on Duplex pipes and have remained blissfully unaware of this misconception. It seems that the problems encountered affect some types of clamp-on flowmeters more than others.
Products such as Duplex, Super-Duplex and high chromium stainless steel have proved popular in the offshore and petrochemical industries for use in pipes, flanges and fittings, owing to their strength and excellent pitting and corrosion resistance. Unfortunately, the properties that make these materials ideal for offshore use also make them expensive, difficult to weld and harder to work with than standard fittings. Consequently, any instrument that could be mounted externally on the pipes would have obvious advantages.
Customers such as BG Group and ConocoPhillips have had Katronic flowmeters installed on their Duplex pipelines for a number of years. Gordon Robinson, Juno Commissioning Manager for BG group, described himself as "extremely satisfied" with the performance of the flowmeters and added "the Katronic system obtained the required accuracy with existing pipe work that seemed unachievable by others". Proof, if proof were needed, that whilst some people might think that clamp-on flowmeters are not suitable for Duplex piping, there is at least one company that knows differently.
