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Emissions

Emissions

Emissions

(OP)
In one of the project, for the 96% sulphuric acid service and caustic service, the client specification is asking to comply with the Fugitive emissions class A for the valves. As for as i understand, is the above chemicals that are in liquid state are to be considered under Fugitive emissions category?

May i know is there any specific reason for this?

RE: Emissions

Hi,

It is not in direct relation with the medium and or the state of the medium. Its more about the Bureau of safety environment reference to ensure that hazardous material “kept within” the valves (with very small leakage tolerance near neglectable) until valves reaches its end of lifetime.
It is arguable, but I think this is the basis for ISO 15484-1 to define mechanical cycle for isolation (On/off) valve which is 205 and for control valve is 20,000 cycles. Most valves guru will support the idea that exceeding this cycle number in actual Plant will requires valves either to be renewed or to be refurbished. Or at minimum to be inspected
Most sulphuric acid, Hydrofluoric acid, ethylene oxide, and many nasty services Plant are built within the agreement between local/national safety bureau and end user. And in summary that end user will comply to install valves that meet fugitive emission specification.

And institution such as TuV, Shell with its type approval test, and others usually assess valves' prototype fugitive emission test with such mechanical cycle in combination thermal cycle (from ambient up to 400 degC). And during all this cycles, the fugitive emission must be smaller than 1 x 10-6 atm. cm3/s (per cm stem diameter). Trust me, if valves do not have consistent and firm tolerance over gap between packing vs stem vs gland housing as well as good quality of packing, valves will not pass this test.
Passing this test, usually justifies the following production batch’s fugitive test may be performed at room temperature and minimum cycle (5 to 20). Under the assumption that dimension, roughness and packing quality is managed as its previous prototype valve. For period, up to xxx years.

How about Liquid phase medium e.g. heat transfer oil, sulphuric acid and HF (inside pipe is liquid, but usually form hazardous cloud upon release), etc.?? Since end user believe that production valves are also built with such quality (and will survive up to 400 degC), then end users’ internal procedure often adapted to justify the desired quality.

The ISO 15484 test is performed with Helium as testing medium and measured by mass-spectrometer. It would be very hard near impossible to measure hydrogen, sulphuric acid, and others gland leakage rate with “helium” mass-spectrometer. Plus, it would be un-economical.
That small number of “laboratory” leakage rate will start to increase significantly once valve met with high temperature and real service medium, in contact with rain lead to corrosion, etc. Then ppm gun (less accurate in comparison with mass-spectrometer) or FLIR camera further on used by Plant inspector.

So, it is a threshold for gland leakage once valve came out from the factory. And assurance for quality over valves external sealing component.
Maybe others have different constructive experiences or view

Kind regards,
MR

https://nosuchvalve.com
All valves will last for years, except the ones that were poorly manufactured; are still wrongly operated and or were wrongly selected

http://www.eng-tips.com/faqs.cfm?&rat1=2&f...

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