PSI - Issue 42

Snezana Kirin et al. / Procedia Structural Integrity 42 (2022) 351–355

352

2

Author name / Structural Integrity Procedia 00 (2019) 000–000

Outer protective pipe

Inner protective pipe

Spolj n a zaštitna cev (udubljenja i rupe ) Outer pr tective pipe (pits and cr vices)

Inner protective pipe (outer corrosion)

Outer protective pipe (inner corrosion)

Inner protective pipe (inner orrosion)

Unutrašnja zaštitna cev unutrašnja ko

Spolj na zaštitna cev U nutrašnja

Outer protective pipe Outer corrosion

Spolj n a zaštitna cev S poljna korozija

Tubing Inner corrosion

P roizvodna cev (

Unutrašnja korozija

Jednostruka Single protective pipe (pits and crevices) Udubljenja i rupe

Single protective pipe Outer corrosion

J ednostruka zaštitna cev S poljna korozija

Single protective pipe Inner corrosio n

J ednostruka zaštitna cev U nutrašnja korozija

Fig. 1 Corrosion occurrence in oil rig pipes, [6] Partial pressure of carbon dioxide and pH-value of water are considered to be the most important criteria for the initiation of corrosion due to the presence of carbon dioxide [1,5]. Carbon dioxide dissolves in the presence of water thus creating the carbon acid which decreases the pH-value of water and supports the initiation of corrosion. The most common types of corrosion which occur due to the influence of carbon dioxide are pitting and crevice corrosion. Examples of fractures due to the existence of the initial crack, influenced by corrosion and fatigue, are presented in Fig. 2

Fracture due to fatigue corrosion

Fracture due to fatigue and stress corrosion

Fracture due to stress corrosion

Fig. 2. Different types of fractures due to corrosion in oil rig pipes

Numerous papers have been published on pipe integrity problems and failures due to cracks and other defects, including corrosion, [11-16]. Nevertheless, all of them lack a comprehensive approach, which would include experimental, numerical and analytical approaches to the problem of corroded pipes and the remaining pipe strength. Toward this aim, several papers were published in the last decade by the authors of the present study, [17-20], including previous experimental investigation on the pipe taken from exploitation in an oil drilling rig after 70,000 hours (8 years) of service [21-23]. In the present paper, the new method, based on risk assessment, using simple engineering procedure for both static and amplitude loading, [24], is applied to API J55 steel pipes, to evaluate corrosion effect. 2. Structural integrity assessment Main technical characteristics of the oil rig pipes used in this research: • working pressure: maximum=10.01 [MPa], minimum=7.89 [MPa]. • number of strokes of pump rod: n=9.6 [min -1 ] Prototype has been made and tested, as explained in [21, 23] and shown in Fig. 3