API STD 6X-2019 pdf download.Design Calculations for Pressure-containing Equipment.
1 Scope This standard describes a design analysis methodology and requirements that apply to design verification of certain pressure-containing products and equipment in the oil and natural gas industry. The methods included in this document apply to designs where normative reference to this standard is made in an API product specification and to those components for which the methods of this standard are required or permitted. Fatigue analysis is outside the scope of this document. Bolting allowable stresses are given in API product specifications and are outside the scope of this document. 2 Normative References The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies, except that new editions may be used on issue and shall become mandatory upon the effective date specified by the publisher or 1 2 months from the date of the revision (where no effective date is specified). API Specification 6A, Specification for Wellhead and Tree Equipment 3 Terms, Definitions, and Symbols 3.1 Terms and Definitions For the purpose of this document the following terms and definitions apply. 3.1.1 elastic analysis Method of structural analysis based on the assumption that the material has a linear elastic stress-strain relationship and therefore does not account for yielding or plastic behavior. 3.1.2 extreme conditions Conditions due to specified events such as seismic loading, wind loading, and wave loading in which loading is additive to the normal loading at operating conditions. See 188.8.131.52. 3.1.3 gross distortion Distortion to the extent that the product no longer functions as intended.
3.1.6 limit analysis Special case of plastic analysis that uses elastic–perfectly plastic material properties and small-displacement analysis to calculate the collapse load using a lower-bound approach. 3.1.7 operating conditions Any combination of internal and external pressures, temperatures, and applied loading to which the product is to be exposed in service, excluding hydrostatic shell testing. 3.1.8 plastic analysis Method of structural analysis by which the structural behavior under given loads is computed by considering the actual material true stress–true strain curve or an elastic–perfectly plastic material and may assume small or large deformation theory as required. 3.1.9 pressure-containing Component whose failure to function as intended results in a release of retained fluid to the atmosphere. 3.1.10 ratcheting Progressive plastic deformation caused by cyclical thermal and/or mechanical stresses. 3.1.11 small-displacement analysis Finite-element analysis wherein the stiffness of the elements is calculated based on their initial undeformed geometry. 3.1.12 stress intensity Equivalent intensity of combined stresses at a point based on the maximum shear theory of failure. The stress intensity is twice the maximum shear stress or the algebraic difference between the maximum and minimum principal stresses at a point. 3.1.13 von Mises equivalent stress Effective stress in a unit volume at which yielding is predicted according to the maximum distortion–energy theory. 3.1.14 yield strength Stress level at which material plastically deforms and does not return to its original dimensions when the load is released based on the 0.2 % offset method in accordance with ASTM A370 or ISO 6892-1 .
4.6 Serviceability Criteria Serviceability criteria that ensure the performance and functionality of the product, as defined by the manufacturer, shall be satisfied at critical locations when subjected to the operating and hydrostatic test conditions. NOTE Examples of serviceability criteria are limits on deflections or rotations that may cause leakage or operational concerns. 5 Elastic Analysis 5.1 Stress Limits 5.1.1 General For elastic analysis, stress components shall be calculated, combined, and then compared to limits for each category of stress based on multiples of the design stress intensity, S m , for the material in use and for the category of stress. For API 6A equipment, standard and non-standard materials shall be as defined in API 6A and the corresponding design stress intensity per 5.1 .2 or 5.1 .3 shall be used. For other equipment, the design stress intensity per 5.1 .2 shall be used, unless otherwise required by the product specification or manufacturer’s specification.