Issue 52

J. Kasivitamnuay et alii, Frattura ed Integrità Strutturale, 52 (2020) 163-180; DOI: 10.3221/IGF-ESIS.52.14 164 The API 579 standard [15] is a well-known assessment standard, especially in the petrochemical industry since it covers the major damage mechanisms found in this area of application. Since the first edition was first released in 2000, the code has been continually revised, with the most recent third edition of the code published in 2016. For the crack-like flaw assessment module, the code provides necessary assessment information similar to other well-accepted codes, such as BS 7910, R6, and FITNET procedures. The stress intensity factor (SIF) solutions in the API 579 standard support the broadest range of cylindrical components and allow the calculation of SIF due to an arbitrary stress distribution profile [16]. The latest edition of standard revised a number of elements, for example, the reference temperature for a level 1 assessment, the recommended residual stress profiles, and the method to determine the plasticity correction factor. The FFS software developed based on the API 579 standard is rarely found in the literature [9, 11, 12]. Furthermore, the available software can assess up to level 2 and do not support the latest edition of this standard. In the development of the FFS software, the extensibility of the software is a necessary concern. Object-oriented (OO) programming is one of the proper approaches that can support the software structure design to satisfy such requirements [17]. A few applications of the OO concept in FFS software for a cracked component were found in the literature [3, 4, 8]. Furthermore, to the authors’ knowledge, the OO concept has not yet been applied in the development of a FFS software based on the API 579 standard. The present paper aims to apply the OO concept to develop the FFS software for a cracked cylinder, based on the latest edition of the API 579 standard. The major concern is to develop a class hierarchy diagram to support the extensibility of the software. The paper is composed of a review of the API 579 standard, the software design process, and an application of the software with example problems. A PI 579 STANDARD he API 579 standard provides three levels of integrity assessment. The higher level of assessment requires more detailed information and analysis, although more precise assessment results can be obtained. Fig. 1 provides an overview of the integrity assessment recommended by the standard. The assessment always starts from level 1 if this level’s applicability criteria are satisfied. The higher level of the assessment should be performed if the lower level assessment predicts a component failure. However, if it is decided not to conduct the higher assessment level, the component must be repaired or replaced as suggested by the standard. An assessment of component acceptability must also consider the potential for future component degradation under continued service conditions, based on the potential for crack growth due to fatigue or corrosion. If there is a potential of crack growth, it is necessary to evaluate its remaining life. The background of the integrity assessment for each level and the remaining life evaluation can be summarized as follows. A level 1 assessment adopts a screening curve approach to determine a permissible crack length in a component. The standard prepares several screening curves according to component geometries (i.e., plate, cylinder, sphere), a crack depth relative to the thickness of the component, and the crack location (i.e., base metal, heat-affected zone, weld). Fig. 2 schematically represents this curve for a particular case. The horizontal axis is T – T ref + 56 (in o C), where T is the component service temperature, and T ref is a reference temperature of the material. The T ref can be set as a nil-ductility- transition temperature, RT NDT , or estimated from the specified minimum yield strength (SMYS) and the exemption curve of a material. From knowing the T , T ref , crack depth, crack location, and component wall thickness, the allowable crack length can be determined from this curve. If the allowable crack length is shorter than that from the inspection, the component is predicted to be unsafe. Level 2 and 3 assessments adopt a failure assessment diagram (FAD) approach. Fig. 3 schematically represents the diagram. The horizontal axis of the FAD is a load ratio based on primary stress, L r , p , while the vertical axis is a toughness ratio, K r . The current status of a cracked component is represented by an assessment point ( L r,p , K r ). The component is predicted to be safe (or acceptable) only if the assessment point lies on or below the failure assessment curve (FAC). Parameter L r,p is defined as:   = , , ref p r p Y L (1) where  ref,p is the reference stress based on the primary stress, and  Y is the yield strength. Equations used to determine the reference stress of a specific cracked component are written in terms of linearized stress components, i.e. the membrane and bending components. T