PED Explorer:- Information

The PED Explorer is based on an Excel spreadsheet produced by Brian Robert's.
The explorer, explores the different inspection module options that the directive permits for a given pressure and capacity.  You can use a higher category of inspection on a lower category of equipment, e.g. you could use module G for any category, even serially produced vessels.

For vessels and steam generators you need to calculate the enclosed volume in litres, and for pipework you need the nominal bore pipe size in mm. If the item could be considered as both pipework and a vessel, take the worst case of both.

Volume Calculator
To help you calculate volume I have included a calculator in the explorer.  It caters for vessels with flat ends, dished ends or a conical end.  For dished ends you require the head height which you can measure or compute, depending on their profile as follows :-
  • 2:Ellipsiodal = Inside Diameter / 4
  • Hemisphere = Inside Diameter / 2
  • Torisphere  = Rs - ((Rs-Di/2) * (Rs+Di/2-2*Rn))^0.5 Or Use the 'Calc' Button

  • Where Rs =  Inside Spherical Radius, Rn = Inside Knuckle Radius, Di = Inside Diameter
    (Note this program will probably overestimate the volume of a Torispherical head as it assumes an elliptical cross section. Click here for further details
The Calculated volume is displayed in the box named 'Capacity'

Using The Explorer
  1. Enter the volume in Litres or Nominal Pipe Size in mm, in the box named 'Capacity'. 
  2. Enter the pressure in barg
  3. Select the button associated with the appropriate chart from the classification table. This will automatically interpolate the graphs in the directive and compute the inspection category, and briefly state the inspection options available.


  • This Explorer is meant to give you a general idea of what the directive requires, you must check that the values calculated and the category selected is correct by referring to the directive before making any decision regarding manufacture. 
  • How accurate does the volume have to be calculated? I don't know, I suggest once you have determined your inspection category, increase the volume by 10% and see if your category changes, if it does use the higher category unless it was SEP then a more accurate assessment of the volume is recommended. The volume for a vessel can include all pipework up to the first termination point / flange. 
  • Generally if the fluid flows through the item its classed as a pipe, if the fluid is stored in the item it’s a vessel.  If the vessel is made out of pipe it is still classed as a vessel.

  • Any data box that is not relevant or zero can be left blank
• PED Explorer     • PED Home Page     • Torispherical Head Profiles Explained
Page last updated 30 June 2002