5 replies to this topic

[peaston]

Hi there, I was wondering if anyone could help me please with work I am doing for a summer placement.

 

I am currently categorising pressure equipment for the Shell Prelude FLNG.

 

My task is to assign a hazard level to all columns, vessels and exchangers in accordance with the AS4343 standard, which is attached.

 

My main problem at current is determining the correct contents and location/service factors and also determining the fluid type.

 

For example, the current vessel I am looking at is an open non-hazardous drain vessel, with a pV value of 35,654 Mpa.Litres and has an operating temperature of 29degC.  The contents of the vessel are water and hydrocarbons, but it does not specify how much HC's there are in any of the design sheets supplied by the vendors. So is this fluid type Non-harmful liquid, or due to hydrocarbon content is it harmful liquid (possiblity of 2 phases, which could mean harmful gas as well?!)?  In each case, a different hazard level is produced.

 

Similarly, a AGR feed separator, containing water, CO2, H2S and HCs is anohter one causingme problems... The density of the substance is 1007 kgm-3, suggesting that it is similar to that of water. with pressures of 7.6 MPa and volumes of 55,200 L ( 419,593.1 MPa.L) at operating temp of 41degC.

 

If anyone could give me some guidance on how to better use this standard it could be greatly appreciated.  It would eb great to see how other engineers make use of this standard, to better my use of it.

 

many thanks

 

Andrew

Attached Files

•  AS_4343-2005_Pressure_equipment_-_Hazard_levels.pdf   885.7KB   89 downloads

[Dazzler]

Hi peaston,

I've done this a few years back so a bit rusty but here are a few thoughts.

• Setup a spreadsheet to record each vessel, and each variable and any remarks or uncertainties.  This will help when you present it to your supervisor, who should check or approve it.
• You could ask for a copy of the "heat and material balance" and matching "process flow diagrams".  Then you can understand what is normally within the equipment item.
• Decide if the composition and properties as your basis are to be for worst case, or for normal case.  Perhaps ask your supervisor first, as it effects your work greatly.
• Decide on worst case phase - liquid or vapour - then just focus on that for each equipment item. 

Dazzler

Edited by Dazzler, 24 June 2013 - 05:36 AM.

[peaston]

Thanks for the reply.

 

I have been using it so far assuming that maximum vapour is worst case scenario, resulting in a using a factor of 10 to the original pV value, which usually results in a higher hazard level.

 

The other issue I forgot to mention was how to use this for heat exchangers.  I have tabulated in my spreadsheet, the pV values for the tube side and heat side  (for shell and tube exchangers), but one source I read to do it for the overall unit, with shell voume - tube volume to be the total volume used for the calculation - can anyone clarify if this seems correct, or should I have a hazard level for both tube and shell side?

[Dazzler]

I don't know the standard, but I would workout and record the two sides separately, but if you do combine them then use the worst case side for PV and toxicity and apply to whole exchanger.

Keep in mind how the results will be used.  Results may effect how intensively the welds and joints on the equipment item are designed and built and then tested (for quality control).  Perhaps ask one of the senior mechanical engineers on the project about the purpose. This may give you some incite into which method is more appropriate.

Dazzler

[peaston]

If there is say, 1/3 of the mixed feed existing as hydrocarbons gas, and the remaining 2/3 water, would you assume it to be characterised by the hydrocarbons, 'Very harmful' as opposed to water as 'non-harmful'?

[Ivank]

_{I know this is well after the original post, but there is a note on determining the harmfulness of mixed contents. The last two lines under Note 1 on page 18 states:}

_{For mixed contents, the harmfulness of the mixture may be determined from the criteria specified in NOHSC:1008. e.g. a mixture of 5% cyanide in water would not be classified as lethal.}