5th Chapter

Question 1

Nominal diameter (DN)

Answer 1

 Nominal diameter is dimensionless → Example: DN 25
 According to the ANSI (American National Standards Institute) the nominal diameter is given in
NPS (nominal pipe size) in inches (1 in = 1“ = 2.54 cm = 0.0254 m)
 A pipe of NPS 2 corresponds approximately to DN 50
 Nominal diameters are stepped that the conveying capacity of a pipeline is increased by about
60 - 100 % for every DN level

Question 2

General recommendations for the use in design estimates

Answer 2

 Water or fluid similar to water 1 - 3 m/s
 Low pressure steam (2.5 bar) 15 - 30 m/s
 Pressurised steam (> 7.5 bar) 30 - 60 m/s
 Air (2.5 - 5.0 bar) 15 - 30 m/s

Question 3

Pipe connections

Answer 3

 Weld joints
 Threaded joints
 Press fitting
 Socket joint
 Flange joint

Question 4

Weld joints

Answer 4

 Firmly bonded connection of pipe sections → most frequently used pipe connection type.
 Complete leakproofness.
 Most secure connection if non-detachable pipes are acceptable.

Question 5

Threaded joints

Answer 5

 An often used (for secondary pipelines in plant construction or domestic installations) and
approved connection method is by threaded pipes and cast iron- or steel fittings.
 If necessary, appropriate sealants (Teflon® tapes, hemp, fibrous webs) are used to achieve a leakproof connection
 High pressures (up to 630 bar): Special pipe screwing (metallic contact or O-rings) can be used

Question 6

Press fitting

Answer 6

 Suitable for thin-walled pipes made from stainless steel.
 Insertion of the pipe ends into a press fitting and subsequent
plastic deformation of a circulatory area with a special gripper.
 No heat source required.
 Leakproofness is ensured by sealing rings.

Question 7

Socket joint

Answer 7

 Elastic socket joints are used for cast iron and plastic pipes
 This allows a slight bending without the application of fittings and
prevents pipe bursts as a result of soil movement (lowering)

Question 8

Flange joint

Answer 8

 Consists of
 Two flanges
 Sealing gasket
 Screws, ring washers and nuts (Always S * 4)
 Careful assembling is mandatory to achieve a
permanent leakproofness.

Question 9

Flat Face (FF)

Answer 9

 Gasket surface in the same plane as bolting circle face.
 Frequently applied when the mating flange or the
flange fitting is made from a casting material.
 Note: FF-flanges are never to be bolted to a raised
face flange (RF)

Question 10

Raised Face (RF)

Answer 10

 Flanges with straight faces (FF or RF) are not suitable
for very high pressures
 Most applied flange type

Question 11

Tongue and Groove (T&G)

Answer 11

 T&G flanges show the best sealing performance and are used for high pressure and vacuum applications
 One disadvantage could be the difficult assembling, as the
joining pipe section has to be pressed apart slightly.

Question 12

Male and Female (M&F)

Answer 12

M&F flanges are comparable to T&G flanges with the exception that they are not used for vacuum.
Commonly found on heat exchanger shells.

Question 13

Ring Type Joint (RTJ)

Answer 13

 Predominately used in gas, oil, petrochemical and offshore industries that involve high pressures and temperatures.
 Gaskets are often metallic sealing rings, suitable for highpressure and high-temperature applications.

Question 14

Advantages of T&G, M&F and RTJ flange faces

Answer 14

 Good sealing properties
 Precise location and exact compression of sealing material
 Use of specialized sealing materials (O-rings)

Question 15

Disadvantages of T&G, M&F and RTJ flange faces

Answer 15

− Commercial availability and costs → raised face flanges are more common
− Application of rigid pipe designing rules

Question 16

Marking of pipes according to fluid transported (Green)

Answer 16

Water

Question 17

Marking of pipes according to fluid transported (Red)

Answer 17

Steam

Question 18

Marking of pipes according to fluid transported (Gray)

Answer 18

Air

Question 19

Marking of pipes according to fluid transported (Yellow or yellow withauxiliary red)

Answer 19

Combustible gases, including liquefied gases

Question 20

Marking of pipes according to fluid transported (Yellow with auxiliary black or black)

Answer 20

Non-combustible gases, including liquefied gases

Question 21

Marking of pipes according to fluid transported (Violet)

Answer 21

Alkalis

Question 22

Marking of pipes according to fluid transported (Brown or brown withauxiliary red)

Answer 22

Combustible liquids

Question 23

Marking of pipes according to fluid transported (Brown with auxiliaryblack or black)

Answer 23

Non-combustible liquids

Question 24

Marking of pipes according to fluid transported (Blue)

Answer 24

Oxygen

Question 25

Applications of pipe-insulation

Answer 25

 Condensation control
 Pipe freezing
 Energy saving as the introduction of thermal resistance reduces the heat flow
 Protection against extreme temperatures
 Noise reduction

Question 26

Insulation materials Lower temperature region (up to about 100 °C

Answer 26

 Rigid-foams made of polystyrene or polyurethane.
 Flexible elastomeric foams based on rubber.
 Flexible polyethylene (PE) forms are commonly used They exhibit a high resistance to the passage of
water vapor → prevent surface condensation even with comparatively small thicknesses. to prevent freezing of domestic water
supply pipelines and reduce the heat loss of domestic heating pipelines.

Question 27

Insulation materials Temperatures up to about 400 - 700 °C

Answer 27

 Shape cups filled with mineral fibres like mineral (rock) wool or glass wool.
 Application temperatures: rock wool ∼ 700 °C, glass wool ∼ 400 °C
 Temperatures up to about 1200 °C: Shape cups filled with high-temperature mineral wool
(ceramic fibres)

Question 28

Trace heating

Answer 28

 Heat tracing or surface heating systems are commonly used to maintain or raise the temperature
of pipes and vessels.
 Protect pipes from freezing
 Maintain a constant flow temperature in hot water systems
 Maintain temperatures for substances that solidify at ambient temperatures or for high
viscous liquids