the many tests and documenting procedures 

 their Undersea Vehicle Safety Standards 

 Committee feels are necessary to assure a 

 safe submersible. 



An indication of the myriad tests followed 

 in submersible construction can be attained 

 from the fabrication steps and tests for AL- 

 VIlS's pressure hull in Table 5.7. At the con- 

 clusion of the tests shown in this table, the 

 pressure hull was considered a part of the 

 vehicle system and tested as such. 



In the course of the pressure test (step 12 

 of Table 5.7) on ALVIN's hull, strain gages 

 were employed, but another technique is 

 used by Perry Submarine Builders which 

 follows a volumetric change in the hull. Both 

 techniques will be briefly discussed. 



Strain Gage Measurements 



As outlined previously, many known dis- 

 continuities are built into the submersible 

 hull, e.g., hatches, viewports, electrical pene- 



trations, welds, etc. Such discontinuities are 

 calculable. To a great degree, verifying the 

 analytical stresses calculated at these dis- 

 continuities is measured by strain gages. 

 Strain gages consist basically of finely- 

 wound wire (the most modern and sensitive 

 employ printed circuit techniques) attached 

 to the hull where changes in their electrical 

 resistance are measured as pressure strains 

 the hull. The resistance change in the gage is 

 subsequently translated to a change in wire 

 length measured in microinches. The final 

 results are then compared with the calcu- 

 lated results to assure that the latter were 

 not exceeded. Placement of the gages is ex- 

 tremely critical to assure that the tests are 

 valid, and all likely stress areas are meas- 

 ured. 



In general, the pressure hull is pressurized 

 externally by some medium (seawater, fresh 

 water) to a proof test pressure (a value calcu- 

 lated in the early stages of design and is 



TABLE 5.7 FABRICATION AND TEST STEPS FOR ALVIN'S PRESSURE HULL [FROM REF. (30)] 



Step 



Inspection and Test 



1. Ingot melt 



2. Roll into slab and flame cut 



3. Spin into hemisphere 



4. Machine internally and mating surface 



5. Weld to form sphere 



6. Machine externally 



7. Cut insert openings 



8. Weld inserts into hull 



9. Clean welds, add hatch, viewports, etc. 



10. Paint to prevent corrosion 



11. Prepare for pressure test 



12. Pressure test 



13. Rework and repaint 



14. Mount into exostructure 



Visual, chemical 



Visual, ultrasonic 



Visual, ultrasonic, temperature 



Dimensional 



XRay, ultrasonic 



Visual, dimensional 



Dimensional 



Visual, XRay, ultrasonic Cocq 



Dimensional 



Visual 



Visual, dimensional 



Visual monitoring of instrumentation 



Visual 



Visual, dimensional fit 



272 



