On Thu, 19 Aug 1999, Crane, Lauren wrote:
> I am working to grasp the implications of the PED (Pressurized
> Equipment Directive) for our equipment.
> I'm stuck on determining the "DN" value for tubing in our equipment.
> I gather from Article 1, 2.6 that DN is Nominal Size, and is a value
> assigned to piping system components.
Dear Lauren:
DN indeed refers to "Nominal Size" and may be thought of a
"Diameter Nominal" expressed in millimeters. It refers basically to
the inside diameter of the tube or pipe. The bigger the pipe, the
bigger the hazard. Length of the pipe does not figure in placing
the piping system or piping run within the Tables.
> 1. 30 psi (2 bar) pneumatic systems in equipment for driving air
> cylinders and air valves and the like fall under the PED according to
> Article 3, 1.3, second indent (group 2 liquids)....correct?
Maybe - see section 3.6 in Article 1, if the pressure
related equipment is no higher than Category I and is evaluated
under the Machinery Directive, then the PED does not apply. Also,
the design of some devices (e.g. internal combustion engines, and
perhaps the cylinders in your equipment) is not determined by the
stresses due to pressure. In those instances, even though the
device contains pressure, they are not expected to be covered by the
PED. See section 3.10 of Article 1 for this exemption - although
the tubing system you referred to is likely to have been designed
with pressure being a controlling factor.
Even if the equipment is covered by the PED, the piping is
not likely to control the classification. At 2 Bar, the piping size
needs to be greater than 500 mm (20 inches) before leaving "SEP" -
Sound Engineering Practices - and entering Category I. 2 Bar times
DN 500 -> 1000 PS*DN.
> . . . if you have a valve with DN=10 and a length of tube
> connected with DN=50, then the system total is . . . ?
In this case, the system will be evaluated using a DN value
of 50, even though the valve is smaller. Again, for piping, DN
refers only to the (largest) diameter, and placement of a piping
system in the tables is determined by the combination of diameter
and pressure. A DN 10 valve with DN 10 tubing results in a DN 10
piping system.
The entire system will be placed in a category that is
determined by the aspect that "earns the highest rating." If the
system contains a vessel at Category II and piping at Category I,
the system is a Category II system.
Regards,
Chuck Seyboldt
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