TCR Arabia in conjunction with its international UK based partner M/s PP SIMTECH undertake FFS Assessment work based on BS 7910 standards (which covers more areas than API 579). Essentially, the fracture mechanics procedure in API 579 is mainly copied / reworded from the procedure in BS 7910 (and previously PD 6493). The BS 7910 fracture mechanics methodology and its application has been successfully proven worldwide by many companies including those in US for at least 35 yrs (from nuclear pressure vessels to high consequence items in the exploration, refining & petrochemical industry, irrespective of the Item code of construction), many times over compared to API 579. The assessment we propose to do is Level 2 to BS 7910.
Fitness for service assessment is performed to make sure that process plant equipment, such as pressure vessels, piping, and tanks, will operate safely and reliably for some desired future period. API Recommended Practice 579 provides a general procedure for assessing fitness for service. The assessment procedure evaluates the remaining strength of the equipment in its current condition, which may be degraded from its original conditions. Common degradation mechanisms include corrosion, localized corrosion, pitting and crevice corrosion, hydrogen attack, embrittlement, fatigue, high-temperature creep, and mechanical distortion. Methods for evaluating the strength and remaining service life of equipment containing these types of degradation are presented and reviewed. Examples are presented to illustrate the application of these methods to process plant equipment.
Process plant equipment is often exposed to corrosive environments and/or elevated temperatures. Under these conditions, the material used in this equipment can degrade or age with time in service. As important equipment such as pressure vessels, piping, and storage tanks become older, the plant operator must decide if they can continue to operate safely and reliably to avoid injuries to personnel and the public, environmental damage, and unexpected shutdowns. Fitness for service assessment procedures provide a means for helping the plant operator make these decisions based on sound, established engineering principles.
Fitness for service assessment is a multi-disciplinary engineering analysis of equipment to determine if it is fit for continued service until the end of a desired period of operation, such as until next turnaround or planned shutdown. Common reasons for assessing the fitness for service of equipment include the discovery of a flaw such as a locally thin area (LTA) or crack, failure to meet current design standards, and plans for operating under more severe conditions than originally expected. The main products of fitness for service assessment are (1) a decision to run, alter, repair, monitor, or replace the equipment and (2) guidance on inspection interval for the equipment. Fitness for service assessment applies analytical methods to evaluate flaws, damage, and material aging.
The analytical methods are based on stress analysis, but they also require information on equipment operations, non-destructive examination (NDE), and material properties. Stress analysis may be performed using standard handbook or design code formulas or by means of finite element analysis (FEA). With modern computer technology, the use of FEA is quite common. Fitness for service assessment requires both knowledge of past operating conditions and a forecast of future operating conditions. Interaction with operations personnel is required to obtain these data. NDE is used to locate, size, and characterize flaws. The material properties should include information of material damage mechanisms and behaviour in the service environment, especially on the effects of corrosion and temperature.