It Doesn’t Get Anymore Severe Than This Service...

Problems in severe service control valves for the oil and gas industry can hinder overall performance due to the tremendous amount of distractions it causes plants and offshore platforms. Having the correct technology is a must when faced with the increased maintenance and operating costs associated with misapplied valves. Statoil experienced this recently when continual problems at their Statfjord ‘B’ were not resolved until they were replaced with custom-designed valves to suite each platform’s specific application needs.

Cavitation and Sand Erosion Problems at Statfjord ‘B’

Few valve applications in oil and gas production are more destructive and require more continuous maintenance than separator level-control valves. Statoil had this experience with separator level-control valves installed at its Statfjord ‘B’ platform in the North Sea.

At Statfjord ‘B’, the output produced by all 13 of its wells flowing through a single separator tank caused severe erosion of the level control valve trim. To control the flow, Statoil previously used two full-capacity valves in parallel, but an improvement wasn’t noticed until Statoil replaced them with a CCI separator level-control choke valve. Cavitation and rapid sand erosion can be eliminated through the DRAG® velocity-control design when combined with advanced materials technology. Figure 1 shows an installed replacement valve that contains the multistage trim.

After six months (twice the previous record and four times the typical normal life span) the valve was reassembled and returned to service for another eight months. On the basis of this, Statoil is replacing separator level-control choke valves on their other platforms in the North Sea with DRAG® velocity control valves.

How Heidrun Plans To Eliminate Emulsification

Another instance where a valve’s ability to provide velocity control is critical is when there is an occurrence of emulsification, whereby the fluid (an oil/water mixture) enters the separator at sizes that are below the separator’s optimum level. Hence, the separator is unable to distinguish the two components present in the mixture. Statoil had an engineering consultant perform a study, where it was determined that the fluid velocity throughout the valve should be kept as low as possible to minimize this problem.

Due to CCI’s reputation as being the only company in the industry to provide a multistage trim in Tungsten Carbide material, and Statoil’s confidence in CCI’s products, Statoil selected CCI’s Severe Service Choke™ for the production choke valves. The fluid velocities exiting the trim of the CCI Severe Service Choke™ are typically 1/3 to 1/4 that of conventional single stage chokes. It is believed that the agitation in the oil/water particles, brought about by the reduction in fluid velocity by the multistage trim, will result in the formation of bigger particles that would be above the separator’s optimum separator level. The valves will be installed in January 2002.

Published in SOLUTIONS Winter 2001