PED 97/23/EC pressure vessel classification

[oosnicram]

Hello

I've found problem with classification of the pressure vessel containg oil (flammable -fluid group I, flaspoint below TS) with TS=200˚C, PS= 10 bar (g), V= 500 l.

PED Article 3, p.1.1
If a fluid has a vapour pressure at the maximum allowable temperature of the equipment of greater than 0.5 bar above normal atmospheric pressure (1 013 mbar), it is treated as a gas, otherwise it is treated as
a liquid.

Bassicaly in my case pressure vapour > 0,5 bar (g) above atm. pressure so fluid should be treated as a gaz and the hazard category should be "IV", but i found guideline 2/8 in Guidelines related to the Pressure Equipment Directive :

"Question: How should a vessel which is intended to contain water below 100 °C
be classified when there is a marginal gas cover?
Answer: This type of vessel is classified according to Table 4, provided the gas is
being continuously removed.
Examples of such vessels are domestic warm water vessels, where
entering air is accumulated on the top, and is normally being removed by
operation."

For water - Pressure vapour at 82°C > 0,5 bar (g)

In my vessel there is a marginal gas cover - it's "almost" completly filled with oil !

May i treat this fluid only as a liquid ? (moreover i can oblige USER in operating manual, to completly fill the veseel)
Hazard category would be "I" and i would save money for Notified Body.

Thank's in advance
oosnicram

 

[Drexl]

If the vapor pressure at TS is > 0,5 bar it should be classified as a gas. It doesn't matter if your vessel is completely filled or not in your case. What matters is that when your tank explodes at TS the contents will flash with hot explosive fumes as a result.

Vapor pressure for water at 82°C is not > 0,5 bar(g), in that case water would boil at a temperature less than 82°C. For a water container with <100°C only the top gas cover will expand as a gas in case of an explosion.

 

[oosnicram]

"Vapor pressure for water at 82°C is not > 0,5 bar(g), in that case water would boil at a temperature less than 82°C."
Do You mean, when vessel is closed ? What of it ? When container is completely filled with water and when we increase temperature above 100°C(e.g. heater), pressure will also increase, but vapor do not appear.

I know that explosion vessel containing vapor i much more dangerous than vessel with liquid , but practically i do not have vapor, when vessel if completely filled !

Moreover boilng point of water = 100°C, b.p. of my oil is > TS ~250°C. All i want to say is that my case is very similar (but higher temperature) to that from guideline 2/8 PED.

Vapor pressure of water :

http://en.wikipedia.org/wiki/Vapour_pressure_of_water

Please look at table - at 80° C p=47,3 kPa = 0,473 bar.

 

[mbt22]

Vapour pressure, absolute pressure at which a liquid boils at a given temperature. 0.473 bar, that is about -0.54 bar(g). They are worried about the liquid flashing or BLEVE if the vessel fails.

As a minor aside, Wikipedia as a source of technical information?

Matt

 

[oosnicram]

For oil i'm waiting for Safety Data Sheet from manufacturer. For water it's just an example.

But yes, You're probably right. Thank's.
Here is another source

http://www.engineeringtoolbox.com/saturated-steam-properties-d_101.html

So, acc. PED Article 3, p.1.1 adequate temperature for 0,5 bar above atmospheric pressure should be 110°C (150kPa=1,5 bar (a)) ? In other words, when i've got a vessel for water and TS > 110°C (0,5bar above atm.) i should consider fluid as a gas ? < 110 as a liquid ?

What is the true meaning of guideline 2/8 ? Now I'm really confused :/

 

[JACKSTAN]

Hello Ooscnicram,
In your case guideline 2/8 is not applicable and the oil vessel falls into cat. IV of PED.
Regarding the water, yes you are right, for TS > 110C water shall be clasified as a gas.

Best regards,

 

[oosnicram]

I got it !

Guideline 2/8 is applicable when a vessel or chamber contains more than one fluid, base the classification on the fluid state that requires the higher category.
Guideline related to: PED Article 9 paragraph 3.

To sum up :
First step - checking fluid group - result : 1 (dangerous) or 2 (others)
Second step - checking if pressure vapor > 0,5 bar (g) above atmosferic pressure at TS - result : liquid or gas
Third step - if pressure vapor < 0,5 bar make sure we do not have additional fluid e.g. air (most cases?) - result : liquid & gas - if so we use higher category - as for gas

Thank's a lot.

 

[europipe]

http://www.lr.org/nl/energy/upstream/documenten/software.aspx

Here's a nice calculator