FACHBERICHTE
Connection, isolation and
repair methods for PE pipings
The pipe material PE has been increasingly used by the supply companies with the beginning extension of the gas supply network
in the 1970s. The reasons for this decision
were and still are the no longer existing corrosion problems, the high flexibility and the
low weight of the material, the high level of
economy and above all a material-appropriate joining method thanks to the fusibility of
the material.
Thanks to the homogeneous fusion of the
PE components, a joint is created which exceeds the long life and durability of the proper pipe: The joint is not the "weakest link in
the chain” of a line but in contrast represents a reinforcement of the pipe.
With the further development of the material types towards a higher strength and also
a higher resistance to external influences as
e.g. grooves, polyethylene increasingly became an interesting material for the water
supply industry. Using electrofusion couplers, pipe joints up to d 710mm are already
possible, and electrofusion fittings such as
e.g. T-pieces or elbows up to d 225mm improve the economic use of this technology in
addition.
Fig. 2: Connection of a gas line
“Fusion with escape of media is impermissible", "problems with residual water" and
"space requirements" are terms that occur again and again in discussions of repair and
connection of PE pipes and piping systems. And rightly so: The cleanness of the surfaces
in the fusion zone is of decisive importance for the achievement of a good and homogeneous weld joint in PE. The following article is intended to illustrate, in a manner orientated to on-site working practice, solutions for the problems involved in re-joining of cut
pipes, repair of local damages as well as the connection of branch elements to pressurized lines. Alternative joining methods, such as clamping-type joints, for example, may
be used with a benefit in particular in repairs thanks to their robustness and their simplicity of use.
Dipl.-Ing. (FH) Robert
Eckert (graduate engineer)
Friatec AG, Mannheim
Phone 0621/486-2214
Email: [email protected]
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But one must remember that inevitably repairs in pipings are and will be increasingly
required because of the larger range of applications despite the special properties of
polyethylene and the continuous further development. Causes for damage could e.g. be
ground movements caused by civil engineering measures in neighbouring piping systems or excavator attacks. But planning, installation and material errors might also be a
cause for required repairs.
In order to be able to perform repairs and
connections of branch lines to existing supply piping systems, the corresponding techniques must be available. For “repair and
connection methods”, butt welding is not
possible for procedural reasons. The electrofusion method as well as mechanical joining
methods offer interesting applications for
this type of use.
In order to obtain a good joint quality in
electrofusion welding, the work has to be
performed thoroughly and above all requires
proper working and preparation. Escaping
media at a repair site are not permissible.
While with regard to natural gas, the safety
regulations to be strictly adhered to are given
priority (BGV-D2; regulations of the safety organisation), not properly sealing isolation elements may cause quality problems because of subsequently flowing residual water
in the field of water supply. Escaping or leaking medium in the joint zone must thus be
prevented in principle during fusion.
FACHBERICHTE
Connections to supply lines
The separation of a line section to perform
connections or repairs in gas or water supply
systems is always connected with a lot of
time and major effort. An interesting alternative to the separation of the line, which results in both a considerable reduction of the
installation costs and does not impair the
supply of the consumer, is offered by PE
spigot saddles with large outlet diameters.
Processing is made using the proven electrofusion method.
Fig. 1: Spigot saddles permit
the efficient connection of
branch lines – even where
large diameters are required.
Isolation options in conventional
connection method
A segmented isolation can be made by
closing of the line valves,
■ pinching off of pipings,
■ installation of shut-off saddles.
■
Pinching off
The pinching off of HD-PE lines is a common practice in gas supply. According to
DVGW leaflet GW 332 (2201) (German Technical and Scientific Association for Gas and
Water), this method is, however, only recommended up to d 160mm with a maximum
wall thickness of 10mm. In order to avoid
damages to the PE line, the maximum pinching off level of 0.8 may not be undershot.
The undefined pinching off of the pipe until
it is completely closed is thus not permitted.
If required, additional measures as e.g. multiple pinching off with intermediate venting
are required. In water supply, the pinching
off method can be used after pressure reduction. But in this case, additional measures may also be required. Subsequently
flowing residual water must be kept from the
fusion zone, e.g. by using a repair sleeve.
The distance between the pinched off site
and the next joint or a further pinched off
site must be approximately the fivefold of the
outer pipe diameter.
Shut-off saddles
Depending on the used shut-off saddle
type and the manufacturer's instructions,
the pressure in the line may amount to a
maximum of 1 bar. A dual isolation with
shut-off saddles with intermediate venting is
e.g. recommended. In the gas supply, special textile shut-off saddles are mainly used
which can also be manually installed in the
low-pressure range. In water supply, resilient
rubber shut-off saddles are available which
mainly cover several dimensions and which
also can be simple installed manually, i.e.
without any additional installation equipment.
Safety measures
In gas supply, all work has to be performed strictly observing the safety measures pursuant to BGV-D2 (UVV50). Fusion
with escaping media is not permissible.
Connections without isolation under
operating pressure
Within the scope of the increasing density
of the network of gas and water supply lines,
the “hot connection” is increasingly becoming of importance, i.e. the installation of a
branch line without interrupting the supply
under full operating pressure of the system.
With the novel spigot saddles (FFig. 1), tappings of up to 123mm are possible under
operating pressure - in connection with an
isolation element. A typical application, the
connection of a gas line, is shown in
Figure 2.
Repair
Mechanical connecting systems
Using mechanical connecting elements
based on clamping or pinching of the pipe,
pipings made of different materials and
whose outer diameters may differ considerably due to standards can also be connected. Mechanical connection elements for PE
pipes are typically deemed having a high tensile strength, even if the transferable forces
are mainly significantly below the pipe
strength. Sealing is made using an elastomer sealing element. In order to counteract the cold flow behaviour of the material,
internal support bodies for the pipe are
sometimes required in case of clamping-type
joints. For minor damages, repair clamps
are available.
Residual water has normally no influence
on the joint quality.
As compared to fusion joints with mechanical connection methods, a service life of the
pipe of up to 100 years cannot be expected.
Clamp fittings for repairs in domestic
water supply
Typically, high tensile-strength plastic
clamp-type fittings (FFigure 3) are used. An
important characteristic of mechanical pipe
couplings to be able to perform a repair siteappropriately using a fitting piece is that the
piece can be slipped on across the entire installation length. By tightening the screw-on
Fig. 3: Repair coupling FRIASAFE
ZRP: High tensile-strength plastic
clamping connectors used as slide
over couplers, especially for the repair
of domestic water connection lines
made of PE
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FACHBERICHTE
The use of plastic clamping connectors is
not permitted for gas lines.
Metal pipe couplings for the connection
of PE water lines > d 63mm
High tensile-strength metal pipe couplings
(FFigure 4) can be easily installed given minor
water leakage and are ideally suitable as
slide over couplers for repairs. Depending on
the design of the sealing and clamping system, modern pipe couplings can be processed today without internal supporting
sleeve with PE pipes of the dimensions SDR
17.6 – SDR 11.
Fig. 7: Schematic view on the use of shut-off saddles for
the repair of a water line
Use of mechanical repair clamps
Fig. 4: Helden Aquafast metal repair coupling – sectional
view
Partial damages in the pipe, e.g. a typical
damage caused by the shovel during a bagger attack, can be repaired using stainless
steel repair clamps (FFigure 5). Depending on
the pipe’s dimension, one-piece or multipart
designs are available. These are installed by
simply tightening the nuts. An important aspect – above all when repairing PE lines – is
a sufficient installation length of the clamp
to exclude creeping of the material at the
damaged site as best as possible. The sealing is made over the entire surface through
the pre-mounted profiled sealing mat specifically developed for this purpose.
Fusion technology
Residual water problem in domestic
water supply
Fig. 5: Qualtight stainless steel repair clamp for PE pipings
cap during the assembly of the fitting, the
grouting of the sealing element is enlarged
at the same time. This dynamic sealing behaviour ensures low installation forces on
the one hand and a reliable sealing even in
cases of unequal pipe surfaces.
When installed, the repair sleeve (FFigure
6) prevents thanks to its integrated sealing
contour that subsequently flowing residual
water reaches the fusion zone. Leak-tightness is even maintained up to a pressure of
approximately 1 bar. A prerequisite for the
use of the repair sleeve is a manageable flexibility of the piping because the corresponding half of the component part has to be inserted by bending the piping. The application is thus limited to pipes of d 32 to d
63mm, SDR 11.
Fig. 6: Installation of
a repair sleeve to
prevent residual water in the fusion
zone.
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Fig. 8: Temporary water retention for the electrofusion welding using a water-soluble film
Residual water problem in pipes
> d 63mm
Use of the saddle installation method
The repair method using a sleeve cannot
be sensibly used in pipes with a diameter
of more than d 63mm because of the reduced flexibility of the pipings and the related installation difficulties. Another option
to keep residual water from the fusion area
is to install shut-off saddles as is common
practice for gas lines. In gas lines, however,
rubber shut-off saddles are used which cover several dimensions because of their resilience. In order to install the shut-off saddle, the piping has to be tapped at first.
The drill should be guided during the tapping process, e.g. by using a spigot saddle
(Figure 1). This spigot saddle can be fused
and be closed by an end cap after completion of the repair. Alternatively, the nonfused spigot saddle can be removed after
tapping and the tapping hole can be closed
by a repair and reinforcing saddle VVS.
FACHBERICHTE
Stagnating water which might occur in the
top area of the spigot saddle is avoided by
using the repair and reinforcing saddle.
The saddle prevents reliably that residual
water may subsequently flow to the connection area. It is to be ensured that no pressure
can build up upstream of the shut-off saddle,
i.e. that retained residual water is drained
through the tapping hole.
After completion of the connection or repair work using fitting piece and slide over
couplers, the saddle is removed and the tapping site is closed as described above (FFigure 7).
After expiry of the cooling time of the component parts and the flushing, the water line
can be commissioned again.
Alternative to the saddle installation
method: the film sleeve
New developments in film engineering offer an interesting alternative to the saddle installation method: Water-soluble films prevent the subsequent flow of residual water
for a defined period of time and then automatically dissolve in water. The film consists
of nontoxic polyvinyl alcohol (PVAL), the carrier film is made of PE material permitted for
use in drinking water applications. To install,
the film sleeve (FFigure 8) is inserted into the
open pipe end. The sleeve is sealed to the internal pipe wall through integrated sealing
lips. After re-connection of the line, the film
residues are removed from the piping during
flushing.
Damage to the pipe surface
Local damages to the pipe surface,
grooves and scratches (according to DVGW
leaflet G 472, grooves and scratches up to
10% of the pipe wall thickness are permissible) or damages which might penetrate
the pipe wall can be repaired using reinforcement and repair saddles or with repair
patches in case of extensive need for repair.
Reinforcement and repair saddles
Damages with a diameter of up to approx.
50mm can be repaired using reinforcement
and repair saddles (FFigure 9). No medium is
allowed to leak during the fusion process. If
required, holes in the pipe wall can be temporarily sealed using PE plugs until the repair has been completed with the fusion
process. It is of importance that the damage
is fully covered by the centric cold zone of
the saddle fusion area of the reinforcement
and repair saddle VSS.
Repair patches
Fig. 9: Reinforcement and repair saddle VVS
Fig. 11: Any extension of the repair area by combi-fusion of
the shoulder area
Repairs of major damages can be performed using so-called repair patches (FFigure 10).
A special feature of the repair patch: The
component part has not only a fusion zone
at the saddle contact area but in addition
also a separate fusion zone at the lateral
shoulder. Thus, any number of repair patches can be lined up and even elongated damages can be repaired such that the original
Fig. 12: Installation of the repair patch by means of toploading using the FRIATOP clamping unit
pipe load-bearing capacity is obtained again
(FFigure 11).
The installation is carried out using the
top-loading procedure (FFigure 12) such that
the joining pressure for fusion is applied
through a centrically acting force transmission.
If damages in the pipe go beyond the area
of the centric cold zone at the saddle and
reach into the heating coil zone or beyond,
the gap between the pipe and the fitting has
first to be closed with PE material, e.g. by extrusion welding.
Conclusion
Fig. 10: Repair patches with separate saddle and “shoulder” fusion area
PE piping systems in gas and water supply
have proven themselves for decades. Despite the excellent material properties, damages in operation can never be excluded.
The repair options presented here using mechanical fittings or the electrofusion method
offer the engineer technically smart and economic alternatives to the traditional, complex repair methods.
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