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Leslie Bottoms |

Are there differences between clamp-on ultrasonic meters used for onshore purposes and those used for offshore projects?

While the basic technology used is the same for onshore and offshore projects, there are some differences between clamp-on ultrasonic meters in these applications.  I’ll take a look at them in a two part blog this week.

Offshore environmental conditions require a higher level of protection from the elements.  The main concern with instrumentation when used offshore is the constant exposure to salt air and sea spray.  This combination can easily corrode housings and cables which are exposed to the elements all day, everyday.  A typical onshore application may involve temperature swings from 20 to 110 degrees F, but in most cases, the instruments used in these locations are generally protected from the sun and rain by sheds or some form of additional shelter.  However, when located offshore, protection is limited to the instrument enclosure, due to size and weight limitations.  In addition, temperatures are often exceeded at both ends of the scale.

Why use clamp-on ultrasonic for offshore measurement applications? 

Due to extremely high process pressures, it is often not possible to utilize conventional inline metering technologies such as turbine, P.D., or Mass meters.  The typical offshore pressure requirements can exceed 5000 PSI and frequently can be up to 10,000 PSI.  Rig operators and engineers prefer Wide Beam ultrasonic technology which has been shown to perform well in these applications without the need to penetrate the process piping.

No pressure, man
For both on and offshore applications the performance requirements are similar.  The operator’s most important objective is to maintain high accuracy flow measurement in situations where temperature and pressure are variable. For Clamp-on meters, pressure is not an issue with regard to installation, operation, and maintenance since the device mounts on the outside of the pipe without the need to interrupt flow or break into the pipe. However, the material specification will vary considerably for the harsher environmental conditions typical on an offshore platform.  In addition, the operational requirements (process conditions) may also be more demanding.  So, let’s start with onshore considerations

Onshore considerations
For traditional onshore use, the requirements are generally limited to environmental concerns and safety issues. 

Here’s how they break down:
1. Environmental concerns
     a. The need for a weatherproof enclosure
     b. Submergibility of sensors and/or cables
     c. Power supply requirements
2. Safety issues
     a. Hazardous area requirements such as; explosion proof, flame resistant, safe area, etc.
     b. Instrument and accessory power protection requirements, such as the use of barriers or intrinsically safe equipment

How do you handle these issues?  Do you use Clamp-on technology in your onshore applications?

Stay tuned!  On Thursday, I’ll examine the more rigorous applications of Offshore operations...

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