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DESIGN INNOVATION PAPERS

Emergency Assessment and Repairs of a Process Tower Subjected to Corrosion Under Insulation

[+] Author and Article Information
Clay D. Rodery

 BP plc, 12000 Aerospace Ave, Suite 325, Houston, TX 77034clay.rodery@bp.com

J. Pressure Vessel Technol 129(3), 541-549 (Nov 06, 2006) (9 pages) doi:10.1115/1.2748838 History: Received January 24, 2006; Revised November 06, 2006

A large process tower in a petroleum refinery was discovered to have severe corrosion under insulation (CUI) in two areas. The areas were confined to the vicinity of external rings, but spanned 360deg of the tower. The remaining thickness of the shell in these areas ranged from 3mm to 9mm (0.13in. to 0.35in.) (original thickness was 23mm(1516in.)). The tower was assessed for immediate risk of collapse and emergency stabilizing bracing was installed while options for a permanent repair could be defined and selected. An external automated weld overlay technique was selected as a permanent repair method that restored the corroded areas to original thickness. This paper describes the engineering process taken to assess the immediate risk of collapse of the tower, including the emergency repairs taken to stabilize the tower. The review and selection of longer term repair options and the analysis involved in coordinating the removal of the emergency repairs with the installation of the permanent repairs in such a manner that the tower was returned to service well ahead of schedule are also covered.

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Copyright © 2007 by American Society of Mechanical Engineers
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Figures

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Figure 1

General arrangement of tower

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Figure 2

Location of areas of CUI

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Figure 3

Area of CUI above ring. (Note excessive scale formation.)

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Figure 4

Measured thickness of upper corroded section (original thickness =(23mm)(15∕16in.))

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Figure 5

Installation detail of stabilizing plates on lower corroded section, showing sequence of installation

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Figure 6

Installation detail of stabilizing plates on upper corroded section, showing sequence of installation

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Figure 7

Full encirclement lap band repair

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Figure 8

Automated weld metal buildup. Note restored shell thickness above the automatic welding rig.

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Figure 9

Installation detail of weld overlay repairs, showing removal sequence of temporary bracing on lower corroded area

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Figure 10

Installation detail of weld overlay repairs, showing removal sequence of temporary bracing on upper corroded area

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Figure 11

Installation detail of weld overlay repairs, showing removal sequence of temporary bracing on lower corroded area

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