Pressure carrying capacities of thin walled pipes suffering from random colonies of pitting corrosion. (September 2018)

• Record Type: Journal Article
• Authors: Soliman, Ahmed A.; Megahed, Mohammad M.; Saleh, Ch.A.R.; Shazly, Mostafa
• Is Part Of: International journal of pressure vessels and piping. Volume 166(2018)
• Page Start: 48
• Page End: 60
• Publication Date: 2018-09
• Subjects: Pitting corrosion -- Burst pressure -- Fitness-for-service (FFS) -- Limit pressure -- Failure pressure -- Nonlinear finite element -- Shell elements -- Thin-walled pipes; FE/FEA Finite element/Finite element analysis -- FFS Fitness-for-Service -- LTA Local thin area -- MAWP Maximum Allowable Working Pressure -- RSF Remaining strength factor -- RSFa Allowable remaining strength factor -- TES Twice elastic slope method; Pressure vessels -- Periodicals; Pipe -- Periodicals; Récipients sous pression -- Périodiques; Tuyaux -- Périodiques; Pipe; Pressure vessels; Periodicals; 681.76041
• DOI: 10.1016/j.ijpvp.2018.08.003
• Languages: English
• ISSNs: 0308-0161

Abstract

Abstract: This paper investigates the influence of widely-spread randomly-distributed pits on the pressure carrying capacity of pipes using nonlinear finite element models for pitting colonies of Grades 1, 2 and 3 of Part-6 of API 579-1/ASME FFS-1 (FFS). Burst pressure predictions for pipes suffering from pitting with increasing severity are obtained and compared with those determined from lower levels of assessment provided in FFS. Upon re-evaluation of standard tabulated values for remaining strength factor (RSF) by means of limit load analysis using FEA for colonies with uniform pit depths, results of Level-1 assessment became more aligned with overall merit of FFS conservatism. For Level-2 assessment, the current investigation showed the need to modulate the conservatism of local thinned areas (LTA) approach. Despite the validity of adopting the LTA check within Level-2 assessment of pitting colonies, the final outcome of the combined RSF is highly conservative compared to RSF estimated by FEA. Highlights: Thin-walled pipes containing random pitting corrosion colonies are assessed using levels 1, 2 and 3 of FFS procedures. Level-3 assessment is conducted using nonlinear FEA where corrosion pits are modeled by shell elements with reduced thickness. Good correlation between PL obtained by the TES method and PF obtained by the ligament stress criterion. RSF values adopted in FFS code for pits with uniform depth should be corrected in order to ensure more realistic level-1 assessment. Consideration of local thin areas (LTAs) in Level-2 assessment provides realistic but highly conservative estimates of RSF.