Specified maximum yield strength

When establishing test pressures for a test section, the maximum test pressure shall be determined by the operator to prevent damage to the pipeline and its components. Consideration must be given to the effect of test section elevation differences on the test pressure. Whenever test pressure will cause a hoop stress in excess of 100% of the specified minimum yield strength (SMYS), refer to Nonmandatory Appendix C for guidance on yield monitoring. The minimum test pressure shall be as required by (a) through (c) below. 

The maximum permitted value for the combined biaxial stress is kST, where S is the specified minimum yield strength per para. PL-3.7.1(a), T is the temperature derating factor per Table PL-3.7.1(g), and k is defined in (b) and (c) below. 

Sm is the maximum allowable operating stress, calculated as specified minimum yield strength x Hf, where Hf is the material performance factor from Mandatory Appendix IX, Table IX-5A or IX-5B. Material performance factors account for the adverse effects of hydrogen gas on the mechanical properties of carbon steels used in the construction of pipelines. 

Lifting lugs attached to the equipment shall be designed using a maximum allowable stress of one-third of the specified minimum yield strength of the material. 

Fy = minimum specified yield strength, ksi a = maximum combined stress, psi Ob = bending stress, psi CTn, r= membrane stress, psi I = moment of inertia, in." ... 

Ultimate strength n. The maximum nominal stress a material can withstand when subjected to an applied tensile, compressive, or shear load. If the mode of loading is not specified, it is assumed to be tensile. In materials that exhibit a definite yield strength, ultimate strength will usually mean the nominal stress at break, which can be less than the maximum. Shah V (1998) Handbook of plastics testing technology. John Wiley and Sons, New York. 

Computed stresses are based on test thickness at test temperature. Since water pressure is a short-term condition, the allowable stresses for structural parts such as supports are frequently increased by a factor of 1.2. The upper limit of stress in the vessel shell during a hydrotest of pressure parts is not specified by the Code. However, it is a good engineering practice to limit the maximum membrane stress in any part of the vessel during a hydrotest to 80 percent of the yield strength. Thermal expansion stresses and local mechanical stresses will be absent and need not be considered. 

Microtensile Specimen n A small specimen as specified in ASTM D1708 for determining tensile properties of plastics. It has maximum thickness 3.2 mm and minimum length 38.1 mm. Tensile properties determined with this specimen include yield strength, tensile strength, tensile strength at break and elongation at break. 

In the case of the example calculations presentexl above a steel with a tonrife yield pomt of 70,000 psi was specified. This would be clai fied as a high-strei th tensile iS eel and would be expected t lE by shear as indicated by Macrae (192) (al sue Table 14.2). Mann (237) concludes that steels with hij tensile strength vriMd be expected to fail by shear. Table 14.4 lists the maximum shear stress and the maximum tensile stri at which ovemtrain was observed to occur fdr vessels of various K ratios fabricated of high-tensile-streid fa steel. 

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