Session: OAC-02-01 Qualification and Testing

Paper Number: 155742

155742 - Fatigue Performance of Cut and Rolled Pipe Thread Connections Installed in LDPE Plant 

Abstract: 

Pipe thread connection provides both mechanical joint and leakproof hydraulic seal. Pipe thread connections installed for newly commissioned Low Density Polyethylene (LDPE) plant were found to be a mixture of cut or machined thread and rolled thread pipe connections, although rolled threads has seemed to be known as industrial practice in LDPE plant. These pipe thread connections are designed for limited fatigue lifetime as they are exposed to cyclic stresses during service. It is understood that cut thread has inferior fatigue performance than pipe thread fabricated by rolled process. Therefore, plant operators foresee challenges in quality assurance of pipe thread connection fatigue performance and risk management with respect to potential premature fatigue failure.  The objective of this study was to investigate the effect of fabrications process including thread type on fatigue performance of pipe thread connection by carrying literature survey.  In addition, laboratory mechanical testing (static tensile, dynamic fatigue, metallographic and fractographic examinations) was undertaken to directly evaluate fatigue properties of specifically fabricated cut and rolled thread specimens.

No significant difference in tensile properties between cut and rolled thread samples was observed, on the other hand, greater fatigue performance was achieved by rolled threads.  Fatigue life at the testing condition of typical operating condition, exceeded 100,000 cycles for both cut and rolled threads, which demonstrated relative low risk of fatigue failure even mixture of two different type of thread connection.

Presenting Author: Ohgeon Kwon Quest Integrity

Presenting Author Biography: Dr Ohgeon Kwon specialises in performance of materials and remnant life assessment in the refinery, petrochemical, and power generation industries. He is also extensively involved in structural integrity assessment and Fitness for Service (FFS) assessment for various components. The assessment involves condition assessment, stress analysis, calculations of maximum tolerable flaw sizes and remnant life assessment under base load and/or cyclic load in accordance with the standard assessment procedures such as API579/ASME FFS-1, BS7910 and R5/R6 codes.

Authors:

Ohgeon Kwon Quest Integrity
Hosea Watson Quest Integrity
Caleb O’byrne Quest Integrity
Sang-Mo Lee SK Energy