ABSTRACT

The problems of instrument an offshore rig are complicated by stringent electrical codes, hostile environment, and operational crew acceptance. Measurements and calculations done with fluidic systems using compressed air as the energy source can be a safe, reliable, and economical solution to many of these problems.

Fluidic systems, while slower than electronics, have acceptable response times for many applications in marine drilling instrumentation. Major advantages stem from their inherent none explosive nature, their resistance to humidity and dampness found in marine operations, their natural dampened systems, and their acceptance by rig personnel. Several fluidic instrument systems used in the drilling operation are reviewed, comparing costs, reliability, and safety with their electronic counterparts.

INTRODUCTION

Instrument problems that are associated with drilling operations, and particularly to offshore operations, are:

  1. explosion-proofing,

  2. reliability and easy maintenance,

  3. survival in a hostile environment,

  4. dampened or arithmetical averaging for vessel motion or sensor response,

  5. simplicity in rig-up, and

  6. rig personnel acceptance.

Apparent that electronics, while providing sophisticated and fashionable solutions, and easily obtainable designs and hardware, have some serious limitations. This is not to imply that the electronics cannot be made suitable for the drilling rig, but rather that there are some good reasons why they should be limited to applications where fluid systems do not provide acceptable response.

The offshore-drilling criteria of explosion proofing and reliability lead to the work that was initially done by NASA on fluidic systems. In the early 1960's the National Aeronautics and Space Administration was faced with some of these same problems while wording with the control and instrumentation of liquid-fueled rockets The science of fluidics was developed by contractors for NASA to resolve these problems.

The basic constraints on the fluidic system was that it be absolutely explosion-proof and extremely reliable. Combining some of these techniques with time-tested "moving-part logic" proved useful in the solutions to many rig instrumentation problems.

Fluidic logic systems use no electricity. Low velocity fluids (or air), and moving parts designed to avoid sparks or heat producing friction, provide an explosion-proof package.

The basic reliability of fluidics and moving-part logic comes from the facts have relatively few delicate part equipments:'" can be easily designed to make use of-rugged components (Fig. 1). Maintenance of properly designed equipment is simple, requiring no specialized tools and consists mostly of cleanup and replacement of diaphragms seals.

The offshore environment is generally considered hostile to equipment because of temperature extremes due to rig relocation, motion of the vessel or impact due either to storms or rig movement, and probably worst of all, corrosion-causing salt spray or salt water (Fig. 2).

These problems are easily resolved in fluidic systems. The fluidic system is unaffected by temperature changes within a wide operational range. Due to the fact that they have no delicate parts, motion and impact pose no serious problems.

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