SIMONA®PP AlphaPlus The new generation of polypropylene Simona PP-AlphaPlus (19 sider).pdfSIMONA Documentation SIMONA®PP AlphaPlus 11/2002. ded, the spherulites might grow up to

Background

Polypropylene is a polymeric material which has been

used for many years in a wide variety of applications.

It has become increasingly favoured for technical pipe-

line systems because of its excellent price/perfor-

mance characteristics [1,2].

Polypropylene (PP), like polyethylene (PE), belongs to

the class of polyolefins which display unusually high

resistance to a broad range of chemicals. The excel-

lent chemical resistance of PP and PE is attributable

to the stable C-C- and C-H bonds in the alkenes and to

their high crystallinity.

Polypropylene is manufactured by polymerising alke-

nes, usually propylene and ethylene. In its pure form

as a homopolymer (PP-H), it consists exclusively of

propylene units (Figure 1).

1

Due to its excellent properties and good price/per-

formance characteristics, polypropylene is gaining

increasing acceptance as the most important mate-

rial for technical pipeline systems. The various types

of polypropylene which have been used up till now

do, however, have their individual material-

related strengths and weaknesses. With the intro-

duction of the new SIMONA® PP AlphaPlus, the mar-

ket has a PP-H 100 type which combines many of the

advantages that up to now were exclusive to indivi-

dual types. SIMONA®PP AlphaPlus has properties

that are superior to the established homopolymeric

polypropylene (PP-H).

SIMONA®PP AlphaPlusThe new generation of polypropylene

Figure 1: Structural formula of polypropylene

H H

H CH3

C C

n

111/2002 Documentation SIMONA®PP AlphaPlus SIMONA

Polymerisation and tacticity

During polymerisation, the methyl groups (-CH3) of

polypropylene can arrange themselves in different

spatial configurations relative to the main carbon

chain (-C-C-) (Figure 2). The way the methyl groups are

ordered is referred to as the tacticity. This results

in different types of polypropylene having different

properties.

In isotactic PP, the CH3-groups are predominantly

arranged on the same side of the main chain. As a

result, the polymer chain coils into a spiral shape so

that the methyl groups are always positioned on the

outside. This helix structure is the reason for the high

crystallinity of isotactic PP.

In syndiotactic PP, the CH3-groups strictly alternate on

opposite sides of the main carbon chain. Due to the

fact that syndiotactic PP has inferior properties to iso-

tactic PP and is difficult to manufacture, syndiotactic

PP is not produced on an industrial scale.

2

The third variant is atactic PP, which has a statistical

CH3-group distribution around the main carbon chain.

Atactic PP is amorphous and has the mechanical

properties of a non-vulcanised rubber. Amongst other

things, it is used industrially for the coating of carpet

backing, as a hot-melt adhesive and as a sealing

compound.

In engineering, apparatus construction and particu-

larly in pipeline construction, only the isotactic form of

polypropylene is of technical importance.

The advantages of isotactic PP over PE-HD are its con-

siderably higher rigidity, strength and hardness (Table

1). As a result, it has a significantly lower notch sen-

sitivity, and the upper limit of the temperature range

within which it can be used is about 20°C higher than

for polyethylene.

Important differences between PP-H and PE-HD are the

higher glass transition temperature Tg (PP-H: 0 °C/

PE-HD: –125°C) and the lower impact strength. In

frosty conditions, a PP-H-100 pipe can fracture if

subjected to mechanical shocks. In particular when

laying pipes at low temperatures, it is therefore less

well suited than PE-HD.

Copolymerisation of propylene with ethylene

The properties of PP-H can be altered by introducing

co-monomers into the polymer chain. All alkenes

can be used as co-monomers, although ethylene is

preferred.

The ethylene interrupts the regularity of the PP-chain

and inhibits the formation of crystalline regions. The

incorporation of ethylene co-monomers into the PP-

chain reduces the glass transition temperature Tg and

so improves the impact strength at low temperatures.

Copolymerisation with ethylene also causes a lowering

of the crystallite melting temperature Tm and hence

lowers the strength at higher continuous application

temperatures.

Being the weaker component in the polymer chain,

ethylene considerably reduces the rigidity and hard-

ness, because the crystallinity is reduced.

Figure 2: Tacticity of polypropylene

Isotactic polypropylene

Syndiotactic polypropylene

Atactic polypropylene

2 SIMONA Documentation SIMONA®PP AlphaPlus 11/2002

3

Classes of polypropylene

Regarding the copolymerisation of propylene with ethy-

lene, a distinction is made between three classes of

polymers (Figure 3). When there is a statistical distri-

bution of the individual ethylene monomers in the

polymer chain the result is a so-called random copoly-

mer (PP-R). This is considerably softer and more

flexible than PP-H but significantly tougher at normal

application temperatures.

A block copolymer (PP-B) is produced via a multi-step

polymerisation process, and involves incorporation

of several ethylene units into the polymer chain in a

closed, compact arrangement. Compared to the homo-

polymer PP-H, this material is more flexible and softer.

When subjected to the creep-rupture internal pressure

test, it does however show poorer behaviour than PP-H.

The special advantage of PP-B is its behaviour at low

temperatures. Compared to PP-R and PP-H it has the

highest toughness at temperatures below 0°C. Table 1

compares various material properties of different

types of PP to those of PE-HD.

PP-H has been very successfully used for many years

for applications in engineering, apparatus construc-

tion and pipeline construction on account of its rigidi-

ty, strength and last but not least its low material cost.

PP-copolymers are less important than PP-H for the

extrusion of sheets and pipes. Due to their high

toughness, PP-copolymers do however have clear

advantages for special applications [4]. The use of

PP-R for the manufacture of thick-walled components

for pipe systems by injection moulding techniques has

become firmly established, largely due to its low ten-

dency to shrink.

Table 1: Properties of different types of PP compared to PE

Property Units PP-H 100 PP-B 80 PP-R 80 PE 80Density, g/cm3 0.91 0.91 0.90 0.95ISO 1183Yield stress, MPa 32 26 22 22DIN EN ISO 527Modulus of elasticity MPa ≥ 1,400 ≥ 1,000 ≥ 750 ≥ 750in tension, DIN EN ISO 527Impact strength, kJ/m2 without break without break without break without breakDIN EN ISO 179Notch impact strength kJ/m2 7 35 25 25at 23°C, DIN EN ISO 179Shore hardness D, 72 67 62 62ISO 868Crystalline melting range, °C 160 – 165 160 – 164 154 – 158 126 – 130DIN 53736

measured on α-crystalline standard PP-H 100

Homopolymer PP-H, Type 1

····-P-P-P-P-P-P-P-P-P-P-P-P-P-P-····

Block copolymer PP-B, Type 2

····-(P-P-E-E-E-P-P)-(P-P-P-P-P-P)-····

Random copolymer PP-R, Type 3

····-P-P-E-P-E-P-P-P-E-P-P-E-E-P-····

P: propylene, E: ethylene (co-monomer)

Figure 3: Monomer sequences in different classes of PP [3]


4

Morphology of the different types of PP

Isotactic PP-H is a partially crystalline polymer that

consists of roughly equal amounts of amorphous and

crystalline regions (Figures 4a and 4b). The ordered

crystalline regions consist of parallel polymer chains.

The chains fold themselves back and so form so-called

folded blocks, which arrange themselves into long

strip-like lamellae with thicknesses of up to 100 nm

(1 nm = 1 : 1,000,000 mm). A certain number of chains

do not fold back, but rather extend to a neighbouring

lamella. The space between the lamellae so consists

of disordered polymer chains, the amorphous region.

The strength of these amorphous boundary layers is

determined by the number of traversing chains and

their loops under each other. In some cases these

boundary layers have to be viewed as weak points –

especially when contacted with media which promote

tension crack formation.

The lamellae grow outwards from a crystallisation

nucleus in all directions in the shape of a star.

Spherical super-lattices form, called spherulites,

which can be easily seen under an optical microscope

because of their size. As a result of the difference in

density between the amorphous and crystalline

regions (Table 2), shrinkage phenomena take place on

cooling the polymer-melt.

The resulting internal stress promotes crack formation

between the spherulites. The danger of tension crack

formation on contact with chemicals is considerably

greater due to the spherulitic structure of the raw

material. The coarser the structure, the more suscep-

tible the pipe to tension cracks. Amorphous materials,

such as PVC or polystyrene, have a lower internal

stress due to the lack of a tendency to crystallise.

Even if it does not go as far as crack formation,

channels form between the amorphous and crystalline

regions on cooling, which manifest themselves as sur-

face roughness on the inner surface of a PP-H pipe

and adversely affect the flow and deposition behaviour

of the medium to be transported.

The way the crystalline structure develops is deter-

mined by the symmetry of the PP-H crystals which are

produced from the melt on cooling the melt down.

Three crystal symmetries are known for isotactic PP-H:

� α (monoclinic),

� β (pseudohexagonal) and

� γ (triclinic)

These differ from each other in their smallest unit, the

unit cell [6].

Figure 4a: Spherulite structure of isotactic PP-H (phase contrast microscope)

Figure 4b: Schematic representation of a spherulite

crystallisation nucleus

amorphousregion

lamellaes


ded, the spherulites might grow up to a size of 1 mm.

Depending on the nucleating agent used, a finer

super-lattice is obtained with spherulites < 50 µm

(mildly α-nucleated PP-H, Figure 5b) and < 20 µm

(β-nucleated PP-H, Figure 5c).

For the last twenty years there has been a commercial

β-nucleated PP-H moulding compound from which

pipes with smoother surfaces are manufactured

[7-10]. This moulding compound possesses a higher

strength at lower rigidity. As Figure 6 shows, the mel-

ting point of the β-nucleated PP-H is approx. 13°C

below that produced from the α-crystalline PP-H

moulding compound. The β-form is thermodynamically

unstable by nature, and there is the danger that it can

convert to the α–form [6, 11-14] if there is cooling of

the melt, such as for example in the welding process.

Therefore, the seams of welded β-nucleated PP-H

pipes predominantly consist of α-crystalline PP-H

[15,16] (Figure 11).

Due to the difference in density between the mono-

clinic α-phase and the pseudohexagonal β-phase,

there are increased stresses in the weld seam, which

are initiated by shrinkage caused by the βα-phase-

conversion during the welding process.

5

The different crystal symmetries of the unit cells give

rise to different crystalline super-lattices, which in turn

lead to clearly perceptible differences in their melting

points and chemical solubilities.

Nucleation and crystallite structure

From a technical point of view, the different crystalline

forms are produced by adding special nucleating

agents to the PP-H moulding compound.

The γ-symmetry can only arise in low molecular weight

PP at high temperatures and is not of interest for prac-

tical application in PP-pipes.

Without the addition of a nucleating agent, isotactic

PP-H almost always crystallises in the monoclinic

α-form. A coarse structure forms, with spherulites up

to 0.1 mm in size (Figure 5a). Ideal conditions provi-

5a: non-nucleated PP-H

Figure 5: Photographs taken under an optical microscope ofPP-H 100 types with and without nucleating agents.

5b: β-nucleated PP-H

5c: mildly α-nucleated PP-H 5d: SIMONA®PP-H AlphaPlus

Polymer Density in g/cm3

crystalline region amorphous region

PP-H isotactic 0.937 0.854

Table 2: Density of the amorphous and crystalline

regions of PP-H [5]


200 µm

The notch impact strength of β-nucleated PP-H accor-

ding to DIN EN ISO 179 is higher than that of α-crystal-

line PP-H. This is partly due to the finer crystalline

super-lattice of the β-form compared to non-nucleated

or mildly α-nucleated PP-H-form and partly due to

conversion to a βα-phase during the impact effect

[11-14]. A portion of the impact energy is used for

transforming the β-crystallites into more dense α-crys-

tallites.

In technical literature there are many references to the

higher solvent resistance and higher resistance to

inorganic acids of α-spherulites compared to β-sphe-

rulites [17-19]. Especially for the morphology tests,

pressure-plates were stored in toluene, carbon tetra-

chloride, benzene, concentrated nitric acid and

6 molar chromic acid at higher temperatures in order

to dissolve the β-spherulites out of the surface of the

plates. The α-spherulites can withstand this etching

process without undergoing any damage.

The reason for the higher chemical resistance of the

α-crystalline phase is the compact structure, which is

also responsible for the higher density of α-spheru-

lites compared to β-spherulites (Table 2).

SIMONA®PP AlphaPlus combines the advantages

of the α- and β-crystalline forms

Using special nucleating agents it has now become

possible to produce a PP-H with an extremely fine crys-

tal super-lattice in the α-crystalline form: SIMONA®

PP-H 100 AlphaPlus. The spherulites are smaller than

5 µm, so that they are difficult to see under an

optical microscope (Figure 5d). The melting point of

SIMONA®PP AlphaPlus corresponds to that of

commercially available α-crystalline PP-H moulding

compounds (Figure 6). SIMONA®PP AlphaPlus thus

combines the advantages of α-crystalline PP-H with

those of the β-nucleated PP-H type.

6

Figure 6: DSC curves of PP-H types with different nucleation(first heating)

non-nucleated PP-H 100

mildly α-nucleated PP-H 100

β-nucleated PP-H 100

SIMONA®PP-H 100 AlphaPlus

β-peak(about 151°C)

α-peak (about 164°C)


7

Pipes made of SIMONA®PP-H 100 AlphaPlus have an

ideal combination of the properties of standard α-cry-

stalline PP-H 100 pipes and β-nucleated PP-H 100

pipes. Table 3 compares some key properties of these

different pipes.

Nucleation can also increase the toughness. For

example, pipes made of β-nucleated PP-H 100 have a

higher notch impact strength at room temperature,

which approaches that of other PP-H types with

decreasing temperature (Figure 7).

SIMONA® PP-H 100 AlphaPlus now offers users con-

siderably improved rigidity in addition to increased

toughness. This is particularly marked at higher

temperatures (Figure 12). The results of the impact

bending test (according to DIN EN ISO 179) clearly

show that the improved resistance of SIMONA®

PP-H 100 AlphaPlus to impact loads is also main-

tained at lower temperatures.

Properties of SIMONA®PP-H 100 AlphaPlus pipes

Test Units Standard SIMONA®PP-H 100 PP-H 100 pipe PP-H 100 pipe AlphaPlus pipe with β-nucleation

Modulus of elasticity in tension MPa ≥ 1,400 ≥ 1,700 ≥ 1,300Yield stress MPa 32 34 30Notch impact strength at 23°C kJ/m2 ≥ 7 ≥ 8 ≥ 12FNCT 80°C /4 MPa h ≥ 250 > 420 413 [4]Surface roughness Ra µm ≤ 0.8 ~ 0.4 ≤ 1.0

The number 100 expresses the creep-rupture strength of the pipe. The classification was made based on the minimum circumferential stress to be reached in the pipe subjected to an internal pressure by 20°C over 50 years (PP-B 80 and PP-R 80 ≥ 8 N/mm2; PP-H 100 ≥ 10 N/mm2). For pipes with d = 20 – 250 mmAccording to information provided by the manufacturer: Ra approx. 0.3 µm for d = 20 – 63 mm; approx. 0.6 µm for d = 75 – 110 mm; approx. 1.0 µm for d = 125 – 160 mm

Figure 7: Notch impact strength according to the Charpy method

Table 3: Comparison of the properties of different PP-H 100 pipes


8

Figure 8: Comparison of the roughness of different types of PP-H 100 pipes, d = 160 mm

Standard PP-H 100


β-nucleated PP-H 100

Surface roughness

The nucleation variants also enable pipes with

smoother internal surfaces to be manufactured.

Figure 8 compares the roughness of different types of

PP-H 100 pipes. SIMONA® PP-H 100 AlphaPlus pipes

have surface roughness values (Ra) of 0.4 µm – a clear

improvement on roughness values achieved up till

now. The reason for this improvement is the uniform,

very fine supper-lattice structure on the internal surfa-

ces of the pipe over the entire wall thickness. The

positive effect of the nucleation of SIMONA®PP-H 100

AlphaPlus on the roughness of the surfaces is clearly

seen on SEM-micrographs (Figure 9).


Uniformity of the super-lattice structure

The values of property parameters are largely de-

pendent on the processing technique used for the

extrusion of the pipe and on the pipe size. In particu-

lar for pipes with high wall strengths, there are often

different super-lattice structures. DSC analysis of

conventional commercially available pipes made of

β-nucleated PP-H 100 (size: 250 x 22.8 mm) showed

the presence of little or no ß-crystalline regions on the

internal side of the pipes. In contrast, clearly distinct

β-crystalline regions were observed on the external

side of the pipes. The corresponding DSC-curves are

9

shown in Figure 10. A possible explanation of this is

the non-uniform temperature profile within the wall

thickness during the cooling phase of the pipe extru-

sion process and the resulting βα-phase convertion on

the inner side of the pipe.

In a non-nucleated PP there is a different crystallite

structure due to the uncontrolled crystal growth and

the low heat conductivity (typical of these materials).

In general, relatively fine crystals form on the cooled

external side, whilst a rather coarser super-lattice with

large spherulites forms on the internal side of the pipe

which is warm for a longer period. Cooling stresses

arise due to the different densities of these regions,

and these stresses can considerably affect the suita-

bility of the pipes for applications.

Due to the very uniform and fine super-lattice struc-

ture of SIMONA® PP AlphaPlus, there is a low degree

of stress in the extruded pipe. Any encapsulated

residual stress can be further minimised by suitable

tempering. In SIMONA®PP-H 100 AlphaPlus pipes, no

changes to the crystalline structure take place during

the tempering process.

The different super-lattice structure manifests itself in

the mechanical properties. In the β-nucleated PP-H

100 pipes which have been studied, a higher modulus

of elasticity in traction and lower tensile strain at

break were found in the internal region of the pipe wall

compared to in the external layer.

Thermal stability of the crystalline structure in weld

seams

As already iterated, and as described in various

articles in the literature, the β-form increasingly trans-

forms to the crystalline α-form on being re-heated

[6,11-14]. This behaviour is also found within a

welded joint. The DSC-curves in Figure 11 show the

different super-lattice structure in different regions of

a welded joint. In this case, a butt weld between two

pieces of pipe (size: 110 x 10 mm) made of β-nuc-

leated PP-H 100 was examined. Studies described in

the literature even report complete transformation to

α-crystalline PP in the weld zone [15,16]. This causes

considerably increased stress in the weld seam.Figure 9: SEM-micrographs of the internal surface of different PP-H 100 pipes, d = 160 mm

Standard PP-H 100

PP-H 100, β-nucleated


20 µm


10

Figure 10: DSC-curves of a PP-H 100 pipe, β-nucleated

Figure 11: DSC-curves of different zones of a weld seam for a β-nucleated PP-H 100 pipe

β-peak α-peak

α-peak

β-peak

PP-H 100 pipe, β-nucleated, 250 x 22.8, internal region

PP-H 100 pipe, β-nucleated, 250 x 22.8, external region


11

Excellent mechanical properties

Due to the presence of α-crystallites, the upper limit

for application is guaranteed up to 100°C. The high

modulus of elasticity in tension (≥ 1,700 MPa, see

Figure 12) sets this material apart as a construction

material, as it guarantees improved resistance to

deflection, even at higher temperatures. Indeed, the

modulus of elasticity in tension at 100°C is about

70% higher than that of standard PP-H 100 and more

than double that of β-nucleated PP-H 100 (Figure 12).

The increased impact strength facilitates handling,

even at temperatures down to 0 °C. Under such condi-

tions, standard-PP-H is likely to undergo brittle frac-

ture, but with SIMONA®PP AlphaPlus there is still rela-

tively high strength which ensures there is plastic

deformation. This is shown in Figure 7. The notch

Advantages of SIMONA®PP-H 100 AlphaPlus pipes for processing and application

Figure 12: Modulus of elasticity in tension of different typeof PP (single analysis on pressed sheets)

impact strength drops with decreasing temperature for

all PP-types. The notch impact strength of SIMONA®

PP-H 100 AlphaPlus at –10°C is virtually the same as

that of standard PP-H 100 at 0 °C. This is the reason

the user-friendly ductile behaviour for SIMONA®

PP-H 100 AlphaPlus, which facilitates the laying of

pipes at temperatures down to 0 °C.

Improved hydraulic properties

The fine crystallite structure of SIMONA® PP-H 100

AlphaPlus pipes has a very advantageous effect on

the roughness. The roughness (Ra) is about 0.4 µm

(Figure 8) and is hence e.g. for a pipe d = 160 mm a

factor of two lower than that of α-crystalline PP-H 100

and considerably lower than that of β-nucleated

PP-H 100. As already shown, this is exclusively due to

the crystallisation properties of the material.

Mechanical smoothing of the inside of the pipes is not

necessary.

The energy required for the transport of liquids or

solids is largely dependent on the surface roughness

of the pipe, for any given pipe cross-section. The extre-

mely low roughness drastically reduces the pipe fric-

tion (FR) and reduces the loss of pressure (∆p) by

about 10%. Depending on the flow rate, up to 10% of

the energy can thus be saved for the transport of a

given volume of liquid. The welding bead resulting

from heated-tool butt welding has a negligible effect

on the loss of pressure in the pipe [20].

For applications in the pharmaceutical and food indu-

stries and in semiconductor technology, the extremely

low surface roughness is absolutely necessary in

order to minimise the deposition of particles or bacte-

ria colonies. Polyolefins per se have a low tendency to

bind foreign particles to their surface due to their low

surface tension.


12

Surface roughness can, however, cause deposition of

dirt particles or bacteria. The considerably improved

surface roughness of SIMONA® PP-H 100 AlphaPlus

pipes significantly reduces the adhesion of particles

(incrustations). This allows potential cost savings for

users due to the ability to have longer intervals bet-

ween cleaning treatments.

Outstanding chemical resistance

The improved toughness and low roughness both have

a very positive influence on the chemical resistance.

The minimal roughness reduces the surface area for

attack, so any surface attack takes place at a much

slower rate. The working life of the pipe increases, the

number of required repairs decreases and there is

optimum functioning of the pipeline.

The increased toughness also minimises tension

crack formation, because the material is less notch-

sensitive. In particular in critical zones such as weld

seams and fixed points, where internal tension or ten-

sion from external sources acts, the resistance when

contacted with tension crack promoting chemicals

such as chromic acid, hydrogen peroxide or chlorine-

containing wastewater is considerably increased.

The lower susceptibility to tension cracks is shown by

the FNCT (Full-Notch-Creep-Test) [21]. For this test, a

sample is made in the form of a pressed sheet. It is

provided with a circumferential notch (Figure 13) and

subjected to a tensile stress of 4 MPa in a tension

crack promoting medium (2% surfactant solution) at

80°C.

Compared to standard PP-H 100 with a lifetime

between 250 – 300 hrs, the lifetime of SIMONA®PP-H

100 AlphaPlus is increased to more than 420 hrs.

This is comparable to the lifetime of β-nucleated

PP-H 100 (Figure 14).

The internal structure of the material also contributes

to the increased chemical resistance, especially the re-

sistance to tension crack promoting chemicals. There

is already a reduction in the tension as a result of the

fine crystallite structure of the nucleated material.

Reducing the residual tension

The internal tension, which is dependent on the manu-

facturing process, can be minimised by tempering

below the crystallite melting point. By tempering we

mean deliberate heating of the pipe wall in order to

dissipate internal tension caused by crystallisation

during the cooling down of the melt. In order to dissi-

pate the tension effectively, the material must be tem-

pered at a temperature which lies somewhat below the

crystallite melting temperature. It is important that the

temperature control is exactly adhered to and that no

crystallisation occurs below the given temperature.

One option is to carry out the tempering as a separate

process in a tempering oven, after the extrusion of the

pipe and once the pipe has completely cooled down.

Figure 14: Lifetime of different PP types in the FNCT at 80°C

Figure 13: FNCT samples

2% surfactant solution

F = 4 MPa

circumferential notch


80°C

From an engineering point of view it is, however, more

sensible to have inline tempering immediately after

the extrusion stage, once the surface has cooled. This

enables the internal heat to be utilised in order to

achieve uniform temperature control in the pipe wall.

For this reason, all SIMONA® PP-H 100 AlphaPlus

pipes undergo inline tempering.

The residual tension in pipes is measured by the annu-

lar stress test using the Janson method. Here, a

length of about 100 mm is removed from the tempe-

red pipe and the external diameter (d) of this section

of pipe is measured. A segment of pipe of defined

width (a) (including the saw cut) is then cut out. If

internal tension is present, the resulting gap a‘ in the

piece of pipe narrows. The difference between the

width of the gap a' and the width (a) of the pipe seg-

ment (Figure 15) is proportional to the internal

circumferential stress σJanson.

Studies have shown that a limit value of 2,5 N/mm2

must be maintained in order to largely avoid tension

cracks on being exposed to chemicals. Tempering of

SIMONA® PP-H 100 AlphaPlus in the inline process

generally reduces the residual tension to below

1,4 N/mm2 (Figure 16).

13

Figure 15: Measurement of the annular stress

Weldability and weld quality

The improved toughness of SIMONA® PP AlphaPlus

influences the quality of the weld: normally the weld is

tested in accordance with DVS 2203 in the technical

bending test.

The machine welding process produces a welding

bead. Depending on the development of the welding

bead, a notch, noticeable to a greater of lesser extent,

is produced in the transition from the pipe to the wel-

ding bead. Around these notches there are tension

peaks, which reduce the strength of the joint. In britt-

le material subjected to tensile forces and chemicals,

these also cause cracks.

The tension peaks are reduced by the improved tough-

ness of SIMONA® PP AlphaPlus, and the result is a

considerably greater strength. SIMONA®PP AlphaPlus

hence provides an especially high degree of safety.

This is an important advantage when work is being

carried out on building sites and in places where pipe-

line components have to be welded at points which are

difficult to access.

The improved quality of the weld seams manifests

itself in the very high bending angle, which was mea-

sured in accordance with DVS 2203. The required

minimum bending angle is far exceeded. The result is

an increased margin of safety with regard to the weld

quality.

Figure 16: Measured annular stress in different pipes usingthe Janson method


a – a' sσJanson = E · ——————— · —–

π · d – (a – a') d

Summary

The significantly improved material properties of

SIMONA®PP AlphaPlus have numerous advantages for

users:

� Considerably lower loss of pressure due to

improved hydraulic properties

� Significantly lower risk of deposition of particles

and bacteria (colony formation) due to super-

smooth surfaces

� Potential cost-savings as a result of the increased

intervals between cleaning treatments

� New areas of application due to an extended tem-

perature range from –15°C to +100°C

� Safe laying and assembly of pipes due to the

improved impact strength, even at low temperatures

up to 0°C

� Improved chemical resistance and minimised risk

of tension cracks

� Improved weld quality provides peace of mind

� Higher degree of safety when welding pipes at

points that are difficult to access

� Full compatibility with other PP pipe materials


16

References:

[1] W. J. Brenik; G. Conradt; F. Harries;

B. Westermann, Plastverarbeiter 49, Nr.4, p.40

(1998)

[2] W. J. Brenik; G. Conradt; F. Harries;

B. Westermann, Plastverarbeiter 49, Nr.5, p.84

(1998)

[3] According to DIN 8078: Rohre aus Polypropylen

(Allgemeine Güteanforderungen, Prüfung)

[4] T. Frank, 3R international , Issue 4/5, p.252

(2000)

[5] H.-G. Elias, Makromoleküle, Hüthig & Wepf

Verlag (1981), p.140

[6] F. J. Padden; H. D. Keith, J. Appl. Physics 30,

p.1479 (1959)

[7] S. Schüssler, Chemische Rundschau 25 (1996)

[8] S. Schüssler, Kunststoffe 86 Nr. 8 (1996)

[9] S. Schüssler, Chemie Technik 27 Nr.9, p.106

(1998)

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