API 6A and 17D, specifications provide the design basis for surface and subsea production equipment bolting in the oil and gas industry. These documents provide both design stress allowables and material requirements for bolting. API defined bolt preload requirements are 0.5 times the material minimum yield strength and 0.67 times the minimum yield strength for API 6A and 17D, respectively. The maximum allowable stress in the bolt due to pressure, thermal and external loading is defined to be 0.83 times the minimum yield strength based on the nominal stress in the bolt at the minimum root diameter.
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