ATEX and the Pressure Equipment Directive

[PeterCharles]

It is being suggested by an end user that equipment conforming to ATEX must also conform to the Pressure Equipment Directive since it is being designed to contain a pressure. I thought that this was NOT the case, but currently have mislaid my reference data.

Can anyone provide clarification, with references, as to which is correct.

 

[Raaden]

A component designed to contain a pressure doesn't automatically make it end up in the PED. See page 2 in the linked pdf for PED exceptions.

http://www.inspectagroup.se/downloads/produktblad/158_Pressure_Equipment_Directive.pdf

 

[PeterCharles]

Thanks, but it doesn't actually refer to ATEX which is the nub of the problem for us currently.

 

[Raaden]

Well my experience with ATEX is a bit limited, but I don't believe that it by itself can force you into PED.

 

[davsy]

If the equipment is for use in a potentially hazardous atmosphere and its duty also meets the definition of the pressure equipment directive it would therefore need to comply with both the PED and ATEX and it would need to be shown on the declaration(s) of conformity associated with the CE mark that would also need to be applied.

An example of an item that typically needs both PED and ATEX would be instrumentation such as a pressure transmitter. It needs to comply with the PED because it is installed in a pressure vessel and it needs to comply with ATEX as it is installed in a potentially explosive atmosphere.

If you give more information on what the "equipment" is that you are refering then we could maybe understand and expand further.

Your end user may well be right if the application is both hazardous area and pressure equipment but if the application of the equipment does not involve pressure equipment then it would not have to comply with the PED for that application.

Don't forget there are other directives that may also come into play such as machineries, low voltage and also EMC for equipment used in Europe.

 

[PeterCharles]

After an in depth reading of the PED it has become clear that equipment that needs to be designed as pressure shock resistant under the requirements of ATEX DOES NOT fall within the scope of the PED.
This is common sense as, to take the example of a bucket elevator a machine well known as a source of explosions, while the casing may be designed for pressure shock resistance (if only to a low value due to the provision of relief panels), to expect it to conform with the PED is clearly a non starter economically.
I'm well aware of the EMC Directive, the Low Voltage Directive and the Machinery Directive.

 

[davsy]

PeterCharles

I certainly would agree that a "standard" bucket elevator should not fall into the PED.

As you say even though you can get pressure shocks in a bucket elevator they are designed to operate at atmospheric pressure which is obviously less than 0.5 barg. For the PED anything that is designed to operate below 0.5 Barg falls outside of the requirements.

On the other hand I do know of a plant where a drag chain type conveyor/elevator had to comply with the PED as well as ATEX as the casing was rated and tested for an operating pressure which was >0.5 Barg. That was a little bit of a special though and for a specific application.

At the end of the day as long as you show that your operating and design pressure are normally below the 0.5 Barg then you fall outside the PED.

Hope that helps.

 

[PeterCharles]

The only chain conveyors I know designed to contain high pressures are those feeding coal to coal mills in power stations, and then that only covers pressure shock resistance in the event of an explosion in a mill. The CEGB used to specify 50 psi (like NFPA).

Luckily, I've never had to be involved with chain conveyors/elevators with high internal pressures in normal operation. Hate to think what it does to the cost to comply with the PED!

 

[davsy]

PeterCharles

The example I mentioned was for an edible oilseed, solvent extraction plant where the elevatyor between the extractor and desolventiser had been specified at 1 Barg. I was involved in the overall project but not specifically with the elevator design. I think it was a Tramco type but the casings had to be uprated slightly although it was only around the idler shaft end so it did not have much of a financial impact.

These type of Elevator/conveyor are quite common in our industry and are constructed to be fully vapour/ liquid tight and as such are a pretty heavy construction with gasketed and dowelled body flanges. I don't think meeting the PED was that difficult in the end.

 

[PeterCharles]

I know en-masse elevators handling hexane wet meal on oil extraction plants. They have never had such a high pressure requirement, but have things like all welded casing, 3" bolt pitch casing flanges with gaskets, internal bearings on non-drive shafts, stuffing box seals on drive shafts.

But according to our reading of the PED anything falling under the PED will require serious design, manufacture, quality control and testing according to pressure vessel standards, NOT something that usually falls under the capabilities of bulk material handling machinery manufacturers, and not helped by handling machinery not conforming to the shapes covered by the PV standards.

 

[davsy]

PeterCharles

I agree standard (large capacity/ bulk commodity) hexane extraction plants would not typically have any form of pressure requirement on the elevator, however this was a small scale speciality plant which had a potential for pressurisation during certain "normal" operating states and as such a decision was taken that a PED compliant elevator would be required.

Like I said I was not directly involved in the specific design of the elevator but I don't remember it being difficult to achieve the PED compliance and as I was involved in the overall project management I can tell you there where no "significant" increases in cost due to meeting the PED.

I think the main advantage with this specific elevator was the relatively small size. If I remember correctly it was only a 150mm wide casing. I do remember the bolt spacing on the mating flanges being less than 3" though.

I appreciate that most mechanical handling equipment manufacturers are not normally required to design their equipment to meet pressure equipment requirements but there are plenty of pressure equipment designers out there who can run a set of calculations to select the correct materials, thicknesses and any additional reinforcements etc. Also the fact that a rectangular shell is not typical for a pressure vessel does not make it impossible it just means the PV designer needs to think a little to earn his money.