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What are the Do's and Don'ts regarding subsea fittings?

asked Sep 28, 2015 in Subsea by pasmith (3,320 points)

1 Answer

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answered Sep 29, 2015 by DavidNivola (475 points)

Do's:

  • Where fittings are necessary (e.g., connection to actuator) the fitting type should be SAE thread with 37-degree bottom taper conforming to SAE standard J514, Ferulok, or special Autoclave AF anti-vibration fitting. 
  • Additionally, the J475, SAE straight thread with O-ring should be acceptable on the actuator spring chamber to seachest port.
  • Ferulok tube and reducers should be welded to the back of hydraulic couplers, etc., rather than pipe threaded connections.
  • You should ensure that any type of threaded fitting will withstand external ambient pressure at depth.
  • Fitting assembly torque should be independently verified and sealed/secured to ensure that the fitting has been properly made up and inspected.
  • Some means should be added to all threaded fittings to prevent loosening.  This can be by wire locking, addition of a clamp over the fitting, or some other method accepted by industry.  If wire locking is chosen, it is preferred to be done with 0.035 in. diameter Inconel 625 wire.  This requires that a 0.040 in. (minimum) hole be drilled through at least one corner of the hexagon-shaped portion of each fitting (if applicable).
  • In addition, due to field history, Autoclave AE anti-vibration fittings should also be additionally locked by one of the methods noted above.
  • Further, not wire locking threaded plug fittings into valves is acceptable because the other end is welded to control tubing (with our current specs), which would prevent the plug turning out of the valve.

Don’ts:

  • National Pipe Thread (NPT) fittings should not be used for permanently installed subsea equipment.  The use of Teflon tape, paste, or any other sealant material is prohibited.
  • No 17-4 ph ferules should be used in this application.
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