On July 28, 1992, a pressurized urea reactor exploded after normal working hours at Arcadian Corporation’s (“Arcadian’s”) fertilizer plant in Lake Charles, Louisiana, destroying the facility, injuring six Arcadian employees as well as four employees of other companies in the area and over 90 private citizens.
Mahesh Madhani, a metallurgic failure investigator has been involved in 1000 failure investigations, including investigations involving the analysis of corrosion in austenitic (corrosive resistant) steel.  Madhani testified, without contradiction, that the explosion resulted from the failure of the clip weld-joint and liner above the C-7 circumferential weld. The welds between the sections of the outer shell were numbered C-1, C-3, C-5, C-7 and C-9, from bottom to top.
It was concluded that this serious accident could have been avoided by:
a) shutting down the reactor upon the previous detection of leaks in the vessel’s lining;
b) implementing an adequate program to ensure that the reactor’s leak detection system was properly monitored; and
c) assuring that critical welds were performed according to industry standards and design specifications.

Other Lessons to be learned on can draw from this detailed report are:
i) Any repair / modification should be well described and relevant construction drawings should be updated accordingly
ii) When a weep hole or a leak detection tube shows a leak the plant should be shut down and the leak should be located and repaired. When a leak detection tube first indicates a leak and then stops to show a leak it does not mean there is no leak anymore. On the contrary likely the leak detection system is clogged by crystallization of carbamate and/or urea and more severe corrosion of the carbon steel can take place leading to catastrophic situations
iii) Any HP equipment item with a loose liner should be connected to a proper continuous leak detection system detecting the gaseous leaks, so in an early stage
iv) Any HP equipment item should be internally inspected at regular intervals; Clips of tray support need special attention

Further please be aware that the use of steam in a leak detection system can lead to unacceptable risks; namely stress corrosion cracking of the carbon steel pressure wall from the inside or in the liner, thus in an area which is impossible to inspect.
Finally involve qualified people and companies to do the repair. 

2009 08 Brouwer UreaKnowHow.com Arcadian Urea HP Reactor Explosion.pdf