Pressure Equipment Directive FAQs

November 3, 2009 No comments yet

6 months ago we published our free “Process Engineers Guide to the Pressure Equipment Directive“.  Since then the guide has been downloaded by readers from all around the world.  Many people have emailed us with further questions related to the PED or have requested help with classifying fluids and categorising equipment, so, based on this feedback we have compiled a list of frequently asked questions and answers to share this knowledge.

If you have more questions, please add them to the list.

  1. Does the PED apply to vessels under vacuum?
  2. How is a valve classified under the PED?
  3. How is a heat exchanger classified under the PED?
  4. How should a vessel that contains both a liquid and a gas be classified?
  5. Can the ASME Boiler and Pressure Vessel Code Section VIII be used to design pressure vessel to comply with the PED?
  6. Where can I find a list of notified bodies?
  7. How do I classify a pressure accessory?
  8. Is PED classification required if we already have ISO, API or ASME certification?
  9. When is equipment required to carry CE marking?
  10. Are all dangerous fluids classified as Group 1 fluids?
  11. How should a mixture of fluids be classified?
  12. Are replacements, repairs or modifications to pressure equipment covered by the PED?
  13. Are pipes considered to be “piping” under the PED when they are placed on the market as individual components?
  14. Can you give some examples of pressure assemblies?
  15. Is on site assembly of pressure equipment by the user covered by the PED?
  16. How is the PED enforced in the UK, compared with national legislations in other EU countries?
  1. Rating: +4

    Positive Negative

    Does the PED apply to vessels under vacuum?

    Equipment with maximum allowable working pressures of less than 0.5 barg are exempt from the Pressure Equipment Directive. Such equipment should be designed, built and tested to appropriate standards but this equipment is not covered by the PED.

  2. Rating: +6

    Positive Negative

    How is a valve classified under the PED?

    Valves are usually classified as pressure accessories. However, the PED category of a valve is usually determined based on the valve nominal diameter in which case the classification charts for piping can be used. If the valve has a significant internal volume, the classification should be carried out using the classification charts for both piping and vessels and the higher category selected.

  3. Rating: +2

    Positive Negative

    How is a heat exchanger classified under the PED?

    Heat exchangers are generally considered to be pressure vessels. However, the following type of heat exchanger is treated as piping:
    Heat exchangers consisting of straight or bent pipes which may be connected to common circular headers also made of pipe providing that air is the secondary fluid, they are used in refrigeration systems, in air conditioning systems or in heat pumps and that the piping aspects are predominant.

    For more details see Guideline 2/4

  4. Rating: +3

    Positive Negative

    How should a vessel that contains both a liquid and a gas be classified?

    The vessel should be classified on the basis of the fluid which requires the higher category. The total volume of the vessel should be used to determine the category – not the actual volumes occupied by the individual fluids.

  5. Rating: +1

    Positive Negative

    Can the ASME Boiler and Pressure Vessel Code Section VIII be used to design pressure vessel to comply with the PED?

    National standards and professional codes (including ASME VIII) can be used for the design and manufacture of pressure equipment. However, a notified body may be required to validate the selected approach if the equipment is categorised as Category II, III or IV.
    See Guideline 9/5

  6. Rating: -1

    Positive Negative

    Where can I find a list of notified bodies?

    A list of all EU approved notified bodies is given here: Notified Bodies

  7. Rating: +1

    Positive Negative

    How do I classify a pressure accessory?

    A pressure accessory should be classified based on its characteristic dimension – diameter or volume. If both diameter and volume are relevant, the equipment should be classified according to whichever gives the higher category.

    For example, a valve is usually classified using diameter as the characteristic dimension whereas a filter is usually classified using volume as the characteristic dimension.

  8. Rating: -1

    Positive Negative

    Is PED classification required if we already have ISO, API or ASME certification?

    PED classification is required in addition to other certification.

  9. Rating: -1

    Positive Negative

    When is equipment required to carry CE marking?

    The PED requires equipment that is classified as Category I, Category II, Category III and Category IV to carry CE marking. Equipment classified as SEP must not carry CE marking.

  10. Rating: -2

    Positive Negative

    Are all dangerous fluids classified as Group 1 fluids?

    No. Only fluids classified as:
    • Explosive
    • Extremely flammable
    • Highly flammable
    • Very toxic
    • Toxic
    • Oxidising

  11. Rating: +2

    Positive Negative

    How should a mixture of fluids be classified?

    If a mixture of fluids contains at least one Group 1 fluid, the mixture should be classified as a Group 1 fluid. The exception to this is if the safety datasheet for the mixture allows it to be classified as a Group 2 fluid.

  12. Rating: +3

    Positive Negative

    Are replacements, repairs or modifications to pressure equipment covered by the PED?

    Complete replacement of an item of pressure equipment by a new one is covered by the PED.

    Repairs are not covered by the PED but may be covered by national regulations.

    Pressure equipment that has been modified to change its original characteristics, purpose and/or type after it has been put into service is covered by the PED.

  13. Rating: +3

    Positive Negative

    Are pipes considered to be “piping” under the PED when they are placed on the market as individual components?

    Individual piping components such as pipes, tubing, fittings, expansion bellows or other pressure bearing components are not considered to be “piping” under the PED until they are assembled into a system. However, a single pipe or system of pipes for a specific application can be classed as “piping” under the PED if all appropriate manufacturing operations such as bending, forming, flanging and heat treatment have been completed.

    On this basis, PED classification of general piping stock would not be carried out by the piping supplier. The pipes and components would be classified by the organisation responsible for the “manufacture” of the piping system.

  14. Rating: +0

    Positive Negative

    Can you give some examples of pressure assemblies?

    Examples of pressure assemblies given in the PED guidelines include pressure cookers, portable extinguishers, breathing apparatus, skid mounted systems, autoclaves; air conditioner, compressed air supply in a factory, refrigerating system, shell boilers, water tube boilers, distillation, evaporation or filtering units in process plants, oil heating furnaces.

  15. Rating: -2

    Positive Negative

    Is on site assembly of pressure equipment by the user covered by the PED?

    Pressure equipment assembled on site under the responsibility of the user is not covered by the PED. Usually the separate components of the system being assembled by the user – such as pressure vessels, valves, piping systems – are covered by the PED. The completion of pressure assemblies on site by the manufacturer is covered by the PED.

  16. Rating: +0

    Positive Negative

    How is the PED enforced in the UK, compared with national legislations in other EU countries?

    The PED is enforced in the UK by the Pressure Equipment Regulations 1999. These regulations make compliance with the Pressure Equipment Directive a legal requirement in the UK. Failure to comply with these regulations can result in prosecution and penalties on conviction of a fine, imprisonment or both. Similar legislation has been enacted in all member states of the European Economic Area.

    The central purpose of the PED is to harmonise the national laws of the member states regarding the design, manufacture, testing and conformity assessment of pressure equipment and to remove technical barriers to trade. Therefore, compliance with the PED under any member state's legislation entitles a manufacturer to sell pressure equipment throughout the European Economic Area.


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Overall Heat Transfer Coefficients

October 22, 2009 No comments yet

To carry out quick heat exchanger calculations, an estimate of the overall heat transfer coefficient usually needs to be made.  Some typical values for the overall heat transfer coefficient for a variety of different types of heat exchanger are listed below.

The values can be used in the Blackmonk Heat Exchanger Calculator.

The reference values have been taken from Coulson & Richardson’s Chemical Engineering Vol. 6, 3rd Edition, R K Sinnot.

Shell & Tube Heat Exchangers

Hot fluidCold fluidOverall HTC (W/(m2.K))Overall HTC (Btu/(hr.ft2.F))
WaterWater800 - 1500141 - 264
Organic solventsOrganic solvents100 - 30018 - 53
Light oilsLight oils100 - 40018 - 70
Heavy oilsHeavy oils50 - 3009 - 53
GasesGases10 - 502 - 9

Shell & Tube Coolers

Hot fluidCold fluidOverall HTC (W/(m2.K))Overall HTC (Btu/(hr.ft2.F))
Organic solventsWater250 - 75044 - 132
Light oilsWater350 - 90062 - 158
Heavy oilsWater60 - 30011 - 53
GasesWater20 - 3004 - 53
Organic solventsBrine150 - 50026 - 88
WaterBrine600 - 1200106 - 211
GasesBrine15 - 2503 - 44

Shell & Tube Heaters

Hot fluidCold fluidOverall HTC (W/(m2.K))Overall HTC (Btu/(hr.ft2.F))
SteamWater1500 - 4000264 - 704
SteamOrganic solvents500 - 100088 - 176
SteamLight oils300 - 90053 - 158
SteamHeavy oils60 - 45011 - 79
SteamGases30 - 3005 - 53
DowthermHeavy oils50 - 3009 - 53
DowthermGases20 - 2004 - 35
Flue gasSteam30 - 1005 - 18
Flue gasHydrocarbon vapours30 -1005 - 18

Shell & Tube Condensers

Hot fluidCold fluidOverall HTC (W/(m2.K))Overall HTC (Btu/(hr.ft2.F))
Aqueous vapoursWater1000 - 1500176 - 264
Organic vapoursWater700 - 1000123 - 176
Organics (some non-condensibles)Water500 - 70088 - 123
Vacuum condensersWater200 - 50035 - 88

Shell & Tube Vaporisers

Hot fluidCold fluidOverall HTC (W/(m2.K))Overall HTC (Btu/(hr.ft2.F))
SteamAqueous solutions1000 - 1500176 - 264
SteamLight organics900 - 1200158 - 211
SteamHeavy organics600 - 900106 - 158

Air-Cooled Exchangers

Hot fluidCold fluidOverall HTC (W/(m2.K))Overall HTC (Btu/(hr.ft2.F))
WaterAir300 - 45053 - 79
Light organicsAir300 - 70053 - 123
Heavy organicsAir50 - 1509 - 26
Gases (5 - 10 bar)Air50 - 1009 - 18
Gases (10 - 30 bar)Air100 - 30018 - 53
Condensing hydrocarbonsAir300 - 60053 - 106

Immersed Coils – Natural Circulation

CoilPoolOverall HTC (W/(m2.K))Overall HTC (Btu/(hr.ft2.F))
SteamDilute aqueous solutions500 - 100088 - 176
SteamLight oils200 - 30035 - 53
SteamHeavy oils70 - 15012 - 26
Aqueous solutionsWater200 - 50035 - 88
Light oilsWater100 - 15018 - 26

Immersed Coils – Agitated

CoilPoolOverall HTC (W/(m2.K))Overall HTC (Btu/(hr.ft2.F))
SteamDilute aqueous solutions800 - 1500141 - 264
SteamLight oils300 - 50053 - 88
SteamHeavy oils200 - 40035 - 70
Aqueous solutionsWater400 - 70070 - 123
Light oilsWater200 - 30035 - 53

Jacketed Vessels

JacketVesselOverall HTC (W/(m2.K))Overall HTC (Btu/(hr.ft2.F))
SteamDilute aqueous solutions500 - 70088 - 123
SteamLight organics250 - 50044 - 88
WaterDilute aqueous solutions200 - 50035 - 88
WaterLight organics200 - 30035 - 53

Plate Heat Exchangers

Hot FluidCold FluidOverall HTC (W/(m2.K))Overall HTC (Btu/(hr.ft2.F))
Light organicLight organic2500 - 5000440 - 880
Light organicViscous organic250 - 50044 - 88
Viscous organicViscous organic100 - 20018 - 35
Light organicProcess water2500 - 3500440 - 616
Viscous organicProcess water250 - 50044 - 88
Light organicCooling water2000 - 4500352 - 792
Viscous organicCooling water250 - 45044 - 79
Condensing steamLight organic2500 - 3500440 - 616
Condensing steamViscous organic250 - 50044 - 88
Process waterProcess water5000 - 7500880 - 1321
Process waterCooling water5000 - 7000880 - 1233
Dilute aqueous solutionsCooling water5000 - 7000880 - 1233
Condensing steamProcess water3500 - 4500616 - 792

Free Pressure Equipment Directive Guide

August 7, 2009 10 comments

PEDGuide

Sign up for the free Pressure Equipment Directive guide

twi

Over the last couple of years I’ve worked on a number of projects that have involved the European Union Pressure Equipment Directive (or PED as it’s sometime known).  The Directive is legislation which aims to ensure that pressure equipment used within the EU is safe.  For the process industries, this most often means vessels and piping.

A key part of complying with the PED is to ensure that equipment has been classified correctly.  Basically this classification categorises equipment according to the degree of hazard should the equipment fail.  Equipment in the most hazardous applications, for instance large vessels containing toxic or flammable gases at high pressure, is required to have extensive quality assurance procedures throughout the design, manufacture and testing stages.  Equipment in low hazard applications, such as a small storage vessel for water at low pressure, has less onerous quality assurance requirements.

In the projects I’ve been involved with, equipment classification has been the responsibilty of the process engineers although the information is required by the other disciplines, especially piping and control/instrumentation engineers.  Higher classification requirements also tend to affect equipment cost and delivery, so project managers also have a keen interest!

Given that the PED is a legal requirement, along with potential cost and delivery implications, it is essential that equipment classification is carried out thoroughly and accurately.  To help you classify equipment correctly, I have written a free guide to the Pressure Equipment Directive which is available to download to all Blackmonk email subscribers.

To get your free copy just enter your name and email details into the boxes above or on the right hand side of this page.

I hope you find the guide useful and would appreciate any comments you might have.

Regards,

Simon.


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