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A Subsea Housing Design Checklist
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Considerations > Stress Analysis
> Materials Selection and Corrosion
Design > Seal Design
Loading Considerations
 Has the
housing been designed for the highest practical external pressure?
For instance, if an ROV application, will the housing be rated for
the full tether cable length?
Have fastener loads
due to internal pressure build-up from temperature variations or off-gassing
of internal components been considered? If rechargeable batteries
are being installed you should consider installing a reliable pressure
relief valve.
Have deployment and
recovery loads been analyzed and considered? Will the housing support
the weight of other components during these operations and if so are
the fasteners and lift points sized for this additional load?
Have the loads imparted
by the mounting structure been considered? Will the mounting structure
accommodate the deformation of the housing under pressure?
Have shock and vibration
loads been considered? Is it necessary to isolate internal equipment
from handling shock or the shipboard/ROV vibration spectrum?
How would a catastrophic
failure of this housing impact adjacent equipment? Could a failure
of this magnitude result in a cascading failure of critical systems?
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Stress Analysis
Has a general factor
of safety for this application been established and consistently applied?
Does it reflect the following considerations:
- Cost of failure at the program level
- Level and accuracy of analysis performed
- Material toughness in a sea water environment (sensitivity to
stress risers)
If the housing material
is plastic: has a conservative working strength been established for
this material which includes consideration of time and temperature
effects?
Have stresses at structural
discontinuities and seal areas been looked at in detail? (FEA?)
Has the increase in
both stress and deflection due to all end plate penetrations been
considered in detail? (FEA?)
Will local deformation
(rotation) in seal areas adversely affect the seal pressure rating?
Have all failure modes
been considered and analyzed (shell failure, bucking, tangential moment,
radial moment, flange shear, seat bearing)?
Have all stress critical
calculations been three dimensional and then compared against an established
three dimensional failure criteria?
Will deformation of
the tube and end caps under pressure result in loads on internal components
or structure?
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Materials Selection and Corrosion
Design
Can the subsea housing
material effectively meet the depth requirement and stay within the
system weight budget?
Does the selected
material have a life expectancy in sea water which exceeds your system
operational plans?
Is the base material,
in its planned temper or heat treated state, subject to stress corrosion
cracking?
Is the base material
galvanically compatible with adjacent materials?
Do any all galvanically
dissimilar metals in electrical contact have a favorable area ratio?
If not can they be electrically isolated?
Does the design avoid
or minimize crevices and other potential corrosion initiation sites?
Are through bolts
used in lieu of blind tapped holes wherever possible?
Are stainless steel
inserts used for all threaded holes in aluminum?
Is there a well defined
electrode attachment feature for all anodized aluminum parts?
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Seal Design
Are redundant seals
used wherever possible to maximize reliability?
When redundant seals
are employed, are they different types (one piston, one face, one
crush,….etc) to minimize susceptibility to common failure modes?
Is the seal material
compatible with the all fluids across the entire operational temperature
range?
Has the seal durometer
been selected to provide a reliable seal at maximum pressure while
minimizing installation forces?
Do all piston seals
have generous lead-in chamfers to protect them for pinching during
assembly?
Have all sharp corners
which the seal may come contact with during installation been removed?
Are critical seal
surfaces protected from damage during handling and assembly?
Are there inspection
plans and assembly procedures in place to insure critical surfaces
are not damaged and that seals are lubricated and installed correctly?
Remember 8 out of 13 leaks past o-ring seals result from improper
installation!
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Next, About Subsea Housing Materials
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