3 replies to this topic

[shekhar dhuri]

Hi,

 

I am Process Engineer.

 

We have off-Spec Condensate Storage Tank which might contain > 1000 ppm H2S. Design Condition of the tank are :   Design Pressure  = 25 mbarg / (-)5 mbarg and Design  Temperature = 80 degC. In Process Data Sheet of the Tank, I specified tank as 'Lethal Serivce' application. Since very small amount of the H2S gas or liquid mixed is dangerous to life when inhaled.

 

However this is challeged by Mechanical Engineer. The argument is API -650 Code does not guides / mentions tanks as 'Lethal Serice'. Lethal Serive is specified only for Pressure Vessels.

 

Being Process Engineer, I am not sure about Tank Design Codes etc.

 

Please suggest.

 

Regards,

Shekhar Dhuri

 

[ankur2061]

Shekhar,

 

Strictly going by API STD 650, it certainly does not define "Lethal Service". So if your mechanical engineer is quoting API STD 650, he is right.

 

But 1000 ppm dissolved H2S is indeed very high. So, what is the way out. Some suggestions:

 

1. Install fixed H2S detectors around potential leak-points (flanges, sample points, pump seals etc.) with alarm facility in the Central Control Room (CCR).

 

2. Administrative procedures should be prepared stating that no operator shall approach the tank without a hand-held H2S detector and a "Self-Contained Breathing Apparatus" (SCBA) and the operator shall be trained in the usage of the H2S detector and SCBA in case of an emergency.

 

3. Tank vent should invariably be connected to a sour gas flare system designed for flaring sour gas. A dispersion study is advised to ascertain ground-level concentration of H2S for various leak scenarios including a design worst case (in all probability it would be the leak from the pump seal of the off-spec condensate storage tank).

 

The above measures should help in risk reduction for operations of the off-spec condensate storage tank with high H2S content.

 

Regards,

Ankur.

[fallah]

Shekhar,

 

It is not unusual to consider the lethal service application for off spec condensate tanks in relevant process data sheets and because in these cases internal lining being applied it shouldn't be challenged by mechanical engineer.Indeed, such tanks are to be equipped with nitrogen blanketing system while the relevant vent will be connected to LP flare...

Edited by fallah, 23 October 2013 - 02:37 AM.

[jrtailor09]

Dear shekhar,

 

Please refer thread posted by me. I hope you will get some idea.

 

http://www.cheresour...ice/#entry73189

 

Regards,

Jatin