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API REPORT 19 Document Information:
Title
Strain Gage Test Results for Proposed 1-13/16 and 7-1/16 30,000 psi Rated API Flanges
American Petroleum Institute
Publication Date:
Mar 1, 1981
Scope:
INTRODUCTION
This report contains the results of tests that were performed on prototype 1 13/16 In. and 7 1/16 In. flanges as a part of the efforts of the 30,000 M Flange Task Group, Association of Wellhead Equipment Manufacturers, to establish dimensions and manufacturing criteria for a line of 30,000 psi rated flanges for submission to API. These tests represented cooperative efforts by the several manufacturers who have representatives on this committee.
Harry J. Sweet and Associates, Inc. was contracted to install strain gages at selected locations on the connectors, record strain values during the tests, reduce the data, and report the results. These results were also to be compared with predicted stress values that are presented in a report titled "Finite Element Stress Calculations For a Proposed Line of 30,000 PSI Rated Flanges" by Sweet & Associates, dated December, 1977.
The strain gage data that were taken during the two tests were reduced by means of a Fortran program that calculates stresses corresponding to the measured strain values, tabulates the results, and presents both the measured Strains and corresponding stresses graphically. The graphs are most useful in identifying trends. Actual strain and stress values can, of course, be taken more accurately from the tables.
One important point must be kept in mind by the reader. All stress values are calculated based on linear relationships between stress and strain. The calculated stress values are, therefore, in error for those cases where the material yield strength has been exceeded.
There are those who argue (correctly) that the measured strain values are all that is required for any desired comparisons with analytical results and that allowable strain values would be as meaningful as allowable stress values. Why, then, should we bother to calculate stresses that are simply wrong when the yield strength has been exceeded?
The answer is that the average engineer is accustomed to thinking in terms of stress rather than strain. Thirty thousand psi stress is simply more meaningful to most of us than is one thousand microstrain.
The dimensions of the 1 13/16 In. flanges are shown in Figures 1 and 2. These pieces differed in that one had a standard hub taper while the other had a straight hub. The overall dimensions of both the 7 1/16 In. flanges are shown in figure 3. Only one of the flanges had the radial holes through the flange for hold down purposes.
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