NDLI: Investigation on the Failures Experienced in Deaerators and Solution Recommendation

Content Provider	The American Society of Mechanical Engineers (ASME) Digital Collection
Author	Lim, Aun Ming Yuen, Simon
Copyright Year	2010
Abstract	The internals in the deaerators of a refinery plant were reported to have experienced a series of failures since their installation in 1985. These failures included development of cracks in the floor plates, damage of supports and breakage of fillet welds. Two possible root causes were initially identified; thermal stresses due to transient conditions and flow induced vibration. The former cause was classified as unlikely since the deaerators were always operating on steady-state conditions. No cyclic operating conditions were imposed on these deaerators. Vibrations however posed as the most likely root cause for the series of failures. The refinery plant inspectors reported that vibrations on the deaerators, although have not been measured, could be physically felt. These vibrations appear to be continuous and increase linearly with load. A finite element analysis was performed to determine the natural frequency of the deaerators. Mode shapes predicted from this calculation show that vibrations could have caused the failures of the internals. Furthermore, the lowest natural frequency of the deaerators appeared to fall within the actual vibration frequency on site (∼20 Hz). Although not confirmed, it is highly suspected that the vibration was excited by the flow (low pressure steam). Several repair options were explored to overcome this problem. These options were concentrated in increasing the stiffness of the steam inlet pipe and the deaerator floor. Finite element assessments demonstrated that the current flexible deaerator floor was the reason for the low natural frequency. An option of introducing reinforcement strips to the bottom side of the floor was identified as the best option to increase the natural frequency of the deaerator and this is expected to overcome the vibration problem. Only one vessel was assessed but the results apply to the other vessels since they are similar in design.
Sponsorship	Pressure Vessels and Piping Division
Starting Page	637
Ending Page	642
Page Count	6
File Format	PDF
ISBN	9780791849224
DOI	10.1115/PVP2010-25492
e-ISBN	9780791838785
Volume Number	ASME 2010 Pressure Vessels and Piping Conference: Volume 3
Conference Proceedings	ASME 2010 Pressure Vessels and Piping Division/K-PVP Conference
Language	English
Publisher Date	2010-07-18
Publisher Place	Bellevue, Washington, USA
Access Restriction	Subscribed
Subject Keyword	Strips Vibration Vessels Fracture (materials) Maintenance Flow (dynamics) Pressure Steady state Stress Transients (dynamics) Design Mode shapes Welded joints Flow-induced vibrations Oscillating frequencies Steam Plates (structures) Stiffness Finite element analysis Damage Pipes Failure Thermal stresses
Content Type	Text
Resource Type	Article

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