Condition assessment of damaged elbow in subsea pipelines

Abstract

The evaluation of the performance of aged structures is essential in the oil and gas industry, where inaccurate predictions of structural performance may lead to significant hazardous consequences. Elbows are critical structures subject to continuous corrosion that can lead to a burst or collapse. It is important to be able to predict both burst strength in continually corroding structures and the behaviour of the structures after critical corrosion takes place. Structural failures due to a significant reduction in wall thickness make it very complicated for pipeline operators to maintain pipeline serviceability. This paper discusses the plastic limit pressure of elbows without defects and with several local thinned areas. Finite element analysis (FEA) and the Goodall formula were used to evaluate the new formula. The results of the FEA show that the limit load of elbows under internal pressure differs with position and depth of damage. An empirical formula for the limit load of elbows with local thinned areas is proposed. Eight sizes of elbow were considered in this study, with Rm/t of 5, 6, 7.5, 9, 12, 15, 20 and 25. This range covers most of the piping used in high-pressure environments, such as nuclear and subsea situations. The method of numerical analysis was validated by experiment and with FEA results from the literature. The results of the study can be applied to both the operation and assessment of pipelines. A formula to predict the maximum burst strength of damaged elbows is presented, which will enable more accurate estimates of the time until pipelines need to be replaced or repaired .

Residual ultimate strength of damaged seamless metallic pipelines with metal loss

“…In pipelines, metal loss defects due to mechanical interference may compromise structural safety and lead to large loss of assets [2]. Unlike the widely investigation of corrosion on metallic pipes [3][4][5], the investigation of such metal loss is relative rare due to low probability of mechanical interference. It has been estimated that the failure of oil and gas transmission pipelines that was resulted from structural damage ranges from 55% in the US to around 70% in Europe [6].…”

Assessment of corroded API 5L X52 pipe elbow using a modified failure assessment diagram

“…Extensive studies have been conducted related to the reliability and structural integrity prediction, prevention of corrosion damages, and repair of corroded steel pipelines and pipe elbows [20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37]. Different experimental approaches and tests, numerical analyses, and analytical methods were used.…”

Numerical investigation of residual ultimate strength of dented metallic pipes subjected to pure bending

“…Additionally, standards such as BSI (2005) and DNV (2013) have proposed relevant information for dented pipes to guide the design. Other relevant research on dents and other types of damage can also be seen from Macdonald and Cosham (2005), Gresnigt et al (2007), Mohd et al (2014), Ghaednia et al (2015), Mohd et al (2015), Lee et al (2017), etc.…”