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[SD0775]

Hello,

One of our condensate storage tanks is undergoing a major repair work (annular plate repair) and is approaching completion. This tank is built to API 650 7th edition. Tank diameter is 84 meter. Stored condensate product has SG of 0.72 and RVP of 12 psi. We are preparing for re-commissioning of the tank and a question raised with regards to the need of nitrogen purging/blanketing for the tank before start filling it with condensate. The argument is to displace air/oxygen underneath the roof deck to avoid forming of flammable atmosphere during the first filling. The site have similar experience many years ago when they were recommissioning the other tank after a minor repair work and they did not use nitrogen for purging. They started the re-commissioning the tank with filling fresh water until the inlet nozzle is fully submerged. I understand that the purpose is to prevent condensate splash and water with better electrical conductivity will also help with releasing accummulated static charges from inflowing condensate. I view this method as conservative and may not be practical since large quantity of water will need to be drawn off at later time.

I have few experience in the past when I commissioned styrene tank with internal floating roof and I did not use nitrogen purging nor water during the first filling. What I remember is we controlled the liquid inflow at around 0.6 meter/sec to avoid static charge accummulation since this liquid also have very low electrical conductivity. This velocity is inline with re-commissioning section of API 575, 653 and 2003.

I would like to hear from anyone who has the experience of using nitrogen as part of commissioning process of an EFR tank for storing flammable liquid with similar size in diameter.

My view of using nitrogen is:
1. It may not be effective to create inert atmosphere underneath roof deck with large diameter tank when the tank is empty since nitrogen may not be well dispersed. There are four vents on roof deck that will keep nitrogen escaping.
2. EFR vents are not designed for nitrogen blanket and poor control of nitrogen flow could potentially harmful to mechanical integrity of the tank/roof/seal.
3. It potentially introduces personel safety hazard (oxygen defficiency) especially when entry onto roof deck will be required for inspection during the course of commissioning.

Regards,
SD

[SDJ]

Just wanted to give an update on this subject that the tank was re-commissioned safely following above mentioned API standards without use of nitrogen. External lab test for condensate was done and concluded that the condensate has very high electrical conductivity.

 

Regards,

SD

Edited by SDJ, 07 October 2013 - 11:44 AM.