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Target Flange: a special configuration of blind flange used downstream, facing upstream, to cushion and reduce the erosive affect of high velocity abrasive fluid. This flange has a counter bore filled with lead as illustrated below.
TYPICAL TARGET FLANGE
COUNTER BORE FILLED WITH LEAD
Operators often specify target flanges on outlets opposite the inlets from chokes on manifold buffer chambers, see below.
Experience has indicated to many operators that a sharp "cushioned" 90° turn will last longer in service than a more gradual "sweep" turn that will rapidly erode on its' inside diameter along the outside of the turn radius. Typically a 90° turn in a high pressure, high velocity, line occurs by installation of a tee ( or cross ) with the run connection down stream closed with a target flange, and the discharge turning 90° and exiting the side outlet(s).
The illustration below demonstrates a target flange connected to the downstream run of a studded tee.
The lead filling the cavity ( counter bore ) of a target flange has a characteristic resistance to the cutting force of high velocity abrasive fluid that may pass through a manifold system during a well control event.
Caution: A problem can occur if the lead filling in the cavity of a target flange escapes the cavity and moves into the flow bore blocking the flow. WOODCO USA has a proprietary method for preventing this occurrence, and to date ( 04/05/13 ) we have received no report of such an occurrence with a WOODCO USA made target flange incorporating this lead retention method.
Some operators argue that an empty fluid cushion cavity in a target flange works just as well as it does filled with lead. Currently we have no documented evidence to support this argument, but we have never observed erosion on used flanges that simply have a cavity without lead filling.
TARGET FLANGE WITH
FLUID CUSHION CAVITY
TIPS ON CHECKING TARGET FLANGES AND WELL CONTROL SYSTEMS AFTER A WELL CONTROL EVENT
After any well control event that requires regulating pressure by flowing high velocity fluid through chokes into a buffer chamber ( sometimes referred to as a header ) inspect the system for erosion damage.
Remove the/all target flange(s) and examine the flange face(s) for erosion 1 and/or a loose or extended lead insert. Repair or replace any damaged target flange(s). Examine the interior bore of the unit of equipment accessed by the removal of the target flange(s), use a light and mirror to look for detrimental excessive erosion that may have "thinned" pressure containing walls to the point of making them too weak to function safely should further erosion occur during the next possible well control event 1.
Visual inspection cannot provide adequate inspection of erosion inside of longer spools or the buffer chamber. For these pieces of equipment measure the wall thickness by using an ultrasonic device designed and calibrated for this purpose. Remember that further erosion may occur during the next possible well control event, further "thinning" the wall, so the wall thickness remaining at any location measured should exceed the original manufacturer's minimum design requirements for pressure containment.
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