074-7.2.1 Whenever pressure hull frames are cut, procedures outlined in paragraphs 074-7.2.2 through 074-7.2.10 or other approved procedures shall be used to establish partial hull circularity.
074-7.2.2 As stated in NSTM Chapter 091, Submarine Hull Inspection , existing circularity of each frame being cut shall be established before cutting hull structure. Determining circularity is done so that results of a check made after the repair can be compared with original geometry.
074-7.2.3 When a partial circularity check is made, the check shall be made as close to frames to be cut as is practicable, but not more than 6 inches away. The transverse arc length of the circularity measurement shall be twice the transverse arc length of the proposed cut, but shall not exceed 30 degrees beyond the edge of the pro-posed cut. An example of standard partial circularity check for patch plate replacement is shown in Figure 074-7-1.
Figure 074-7-1 Standard Partial Circularity Check
074-7.2.4 Where tank tops intersect pressure hull, the circularity measurement shall not extend beyond the point at which the tank top intersects the hull. An example of a partial circularity check where the tank top inter-sects the hull is illustrated inFigure 074-7-2.
Table 074-7-1. MEASUREMENTS REQUIRED FOR REMOVAL AND REPLACEMENT OF SUBMARINE HULL PLATING AND FRAMING
The following measurements will be taken
Frame Spacing MIL-STD-1688 X X1 X X X
Frame Depth MIL-STD-1688 X X X X X
Web Thickness Ship’s Drawing X X X X
Flange Thickness Ship’s Drawing X X X X
Shell Thickness Ship’s Drawing X X X X X3
Flange Width MIL-STD-1688 X X X X
Web Tilt MIL-STD-1688 X X X X X X
Flange Tilt MIL-STD-1688 X X X X
Flange Unbalance2 MIL-STD-1688 X X X X
Frame Flange
Figure 074-7-2 Partial Circularity Check Where Tank Top Intersects Hull
*Measurements are required where marked by an X.
**Reference MIL-STD-1688 for definitions and allowable frame dimensions and frame alignment tolerances.
1Only for frame spacing in bays which contain the forward and aft butts of the plate or patch.
3This measurement is required only when existing plating is replace.
2This measurement is required only for fabricated frames.
074-7.2.5 The first step in determining circularity of a frame to be cut is to establish the elevation of points A and B ofFigure 074-7-1andFigure 074-7-2relative to similar points at adjacent undisturbed frames forward and aft of proposed cut. Elevation can be established by the use of optics or by erection of a range wire similar to the example shown inFigure 074-7-3. The elevations (h dimensions) should be recorded for future reference.
074-7.2.6 Next, the existing radial geometry between points A and B of Figure 074-7-1 andFigure 074-7-2 should be established. This can be done by using a template similar to the one shown in Figure 074-7-4. The template can be made of steel, aluminum, or plywood. The template should have a scribed radius which is a known amount greater than design radius of hull to be measured. The template should contain radial scribed lines at 5 degree intervals.
074-7.2.7 Position the template over area to be measured. The template shall stand normal to the submarine main axis and the points of contact between template and hull shall be those points whose elevations were pre-viously measured and recorded. After the template has been positioned properly, a series of measurements shall
Figure 074-7-3 Use of Range Wire To Establish Elevation
Figure 074-7-4 Example of Template Used To Establish Radial Geometry
be taken at the 5 degree intervals indicated on the template. Measurements shall be taken from the hull surface to the scribed line on the template. All these readings shall be recorded for future reference.
074-7.2.8 After the patch has been cut out and rewelded into place, and all adjacent major welding has been completed and allowed to cool to ambient temperature, the procedure shall continue:
1. The range wire, referred to in paragraph074-7.2.5, shall again be erected and the h distances shown inFigure 074-7-3 shall again be measured and recorded.
2. The template shall be positioned over area previously measured and a new set of radial measurements shall be taken at 5 degree intervals and recorded.
074-7.2.9 An acceptable method of recording all measurements is illustrated inFigure 074-7-5. Measurements to be recorded are:
a. Actual measurements of end point elevations and contour taken before cutting should be recorded on line A.
b. Points of contact between template and hull shall be considered to be zero points. Therefore, all readings greater than the distance from the zero point to the scribed line on the template will reveal a dip in the hull and should be considered negative readings. All readings less than the distance from the zero point to the scribed line reveal a bump in the hull and should be considered positive readings. Contour measurements rela-tive to zero end points before cutting should be recorded on line B.
c. Actual measurements of end point elevations and contour taken after rewelding should be recorded on line C.
d. Contour measurements relative to zero end points after rewelding should be recorded on line D.
e. Inspection of existing tabulated information will reveal whether or not there has been any movement of end point elevations. If h dimensions obtained after rewelding deviate from original h dimensions, corrections equal to the deviation shall be added to if h increases, or subtracted from if h decreases, the contour measure-ments recorded on line D. These new corrected contour measuremeasure-ments shall be recorded on line E.
074-7.2.10 When information has been recorded (see Figure 074-7-5), three comparisons shall be made to determine whether or not a full circularity check is required.
a. If any of the contour measurements shown on either line B or D has a magnitude greater than one-half the thickness of the pressure hull plating or 1/2 inch, whichever is less, this shall be a cause for requiring a full circularity check.
b . If the difference between the b dimensions taken before cutting and after welding is greater than 1/8 inch, this shall be cause for requiring a full circularity check.
c. If the difference between contour measurements on line B and those on either line D or E is greater than 1/8 inch, this shall be cause for requiring a full circularity check.
Figure 074-7-5 Method of Recording All End Point Elevation and Contour Measurements Before Cutting and After Rewelding Hull