Some pipe materials are rarely to be found in the water supply. That’s why piping network operators should come to an understanding with these materials. In case of maintenance and repair they could then react correctly and in time. To avoid disagreeable experiences it is highly recommended to dispose of the know-how of leading manufacturers of pipe joining and repair technology.
Differences...
Fibre cement pipe
The pipework inventory of these pipes mainly consists of asbestos cement (AC) pipes which were used until the early 1990s, and their asbestos free successors.
For maintenance and repair works on AC pipes, special prevention measures [1] have absolutely to be observed!
Fibre cement pipes where used in the water supply since 1930 [2] in nearly all diameters. Many of these pipes are still in use without difficulties today. Damages caused by sedi-ments or abrasion are extremely rare to be found. Frequent cases of damage are: ■ Leaky lugs caused by brittle gaskets ■ Leaky lugs caused by stress and/or
angu-lar defl ection
■ Shell break-off caused by punctual stress and tension
■ Soaking of the pipe surface when it is in permanent contact with the ground water A lot of joining methods have been devel-oped for fibre cement pipes [3]. There is not enough space to name all of them. Gener-ally, the plain-ended and calibrated pipes are joined together with push-on couplings. The current types are:
■ SIMPLEX-coupling ■ RINGTITE-coupling ■ REKA-coupling
The REKA type, which features an easy in-stallation as well as a reliable sealing, is most commonly used. The REKA design was taken over for today’s GRP couplings.
Glass-fi bre reinforced plastic pipes (GRP)
Used primarily as a substitute for the asbes-tos cement pipes, GRP pipes have established for various applications in the water supply. Their main advantages are that they can be produced in nearly every required bore and also would withstand a high working pressure even in greater diameters. GRP pipes consist of glass fibre, (polyester) resin and reinforcing materials like limestone or quartz. Typically, GRP pipes are used in diameters larger than DN 300 (Figure 1).
It is important to distinguish between ■ centrifugally cast GRP pipes (e.g. HOBAS)
and
■ fi lament wound GRP pipes (e.g. FLOW-TITE).
This article does not deal with particular prop-erties of these manufacturing technologies but some differences are worth knowing: ■ centrifugally cast GRP pipes have an
abso-lutely plain outside and therefore a clearly defi ned external diameter
■ fi lament wound GRP pipes are coiled around a core which leaves their inside plain and glossy
■ centrifugally cast pipes are made by using chopped glass fi bres, fi lament wound pipes by using endless glass fi bre roving ■ fi lament wound GRP pipes can be suitable
for higher working pressure
When laying new pipe schemes, GRP pipes are usually connected with REKA-couplings. If necessary, pull-out resistant joints working with shearing rods are provided.
Damage caused by corrosions cannot be found with GRP pipes. They offer a high structural stiffness and mechanical strength. Facing a punctual overload, single fibre layers would release from the composite matrix, a process better known as delamination. Leak-ages which arise from delamination appear as areas of “transpiration”, where small amounts of medium drip out of the pipe wall.
Pre-stressed concrete pipes
In the field of water supply, pre-stressed con-crete pipes are mostly used in nominal diam-eters from at least DN 800. For example, the backbone lines of some important European water suppliers [4] are made of pre-stressed concrete.
Dedicated Solutions for
Exceptional Pipe Materials
Considerations for the selection of adequate
joining and repair products for GRP and
concrete pipework
By Sascha Radosevic and Jan Treiber
The article shows how to realise pipe connections and repairs of GRP-, concrete and fibre cement pipes. These pipe materials are more or less uncommon in the water supply. Their special characteristics and typical joining methods will also be illustrated.
Piping network operators using these pipe materials may also be aware of the standard connectors often not to be very useful in case of maintenance and repair. Therefore, great importance should be placed on the analysis of the pipework. The authors display key fac-tors for the professional technical evaluation of the pipelines, as well as they show current „trench-proven“ solutions for the issues mentioned.
Fig. 1: GRP pipe (OD 924 mm, PS 23 bar)
with STRAUB-FLEX coupling
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31 3R international · Special-Edition · 2/2008
Fig. 1: GRP pipe (OD 924 mm, PS 23 bar)
with STRAUB-FLEX coupling
The pipes are manufactured by casting con-crete all around a pre-stressed wire mesh. Different types of pipes can be found, nor-mally labelled by the producer’s name. Some examples: ■ DYWIDAG-Sentab-pipe (DS) ■ Brespa-pipe ■ Zueblin-pipe ■ Arkel-pipe (AR) ■ Bonna-pipe (BO)
These pipes differ in the wire mesh design as well as in the wall thickness, the outside diam-eter and the joining method. Aside the “classi-cal” bell-and-spigot type, a lot of constructions with different functionalities can be found. Typical damages found with pre-stressed concrete pipes are leaky lugs or corroded wires. Leakages of the bell-and-spigot joints are mostly caused by brittle gaskets and/or ground settlement. Rehabilitation can be done in different ways:
■ Lug renovation by using internal sealing devices (e.g. AMEX [5])
■ External sealing of the lug gap
■ Rehabilitation of a whole pipe section using a polyethylene liner [6, 7]
Other nameable damages are circular cracks due to corroded wires [8] or leaky butt joints.
...and similarities
Even if all the named pipe materials may seem to be quite different, they have one thing in common: used as pipelines, they are mostly the backbone mains of the water supply sys-tem. Disruptions as a result of maintenance and repair are always time-critical and should be avoided if possible.
The above mentioned typical pipe joints used with new-laid schemes are often disadvanta-geous for tie-in sections, maintenance and repair because they can neither be slipped over the pipe nor can they be installed into the existing pipework.
Collect data!
Especially the lack of key information will al-low the “worst case” to come to pass. The authors are often confronted even with larger utilities or network operators not understand-ing enough about the state and properties of their pipework. Some even do not dispose of important data which leads to a certain hectic activity in the event of damage.
Specific values of the really important pipe-lines should be well-known or determined at every opportunity. The following pages display a checklist with important evaluation param-eters for pipelines. These paramparam-eters allow to estimate correctly the status quo. In case of maintenance and repair they only have to be completed by the local circumstances (e.g. soil conditions, accessibility).
Global Data
Pipe material
e.g. concrete / GRP / AC...
Coating type
e.g. bitumen / paint...
Measured values
Nominal diameter DN [mm]
Often to be found in the pipewokr plans; relevant for hydraulics engineering.
Wall thickness s [mm]
Important value for the pipe statics and the pressure resistance.
Outside diameter d [mm]
To pinpoint d always means to regard the ovality and the circularity of the pipe!
Misalignment h [mm]
Extremely important fo repairs and when reinstalling pipe sections!
Angular deflection α [˚]
Extremely important for repairs and when reinstalling pipe sections!
Additional parameters and factors
Ovality
Mostly occurs on pipes in larger diameters.
Circularity
Pipes made of GRP, pre-stressed concrete and fibre cement rarely are truly round!
Pipe surface conditions
Spalling of concrete and local damages eventually have to be smoothed out!
Axial elongation and/or movement
Temperature difference will affect the length of the pipes!
Dimensional accuracy
The external siameter of a pipe section – in particular when made of concrete –may rather vary!
At first glance the multitude of parameters and factors seems to be exaggerated. Those who have experienced a construction project being delayed or even interrupted by the una-wareness of these parameters really know about their significance.
The above check list only displays the factors relevant for the daily practice and does not claim to be complete. In the particular case it will be necessary to go further into the details, e.g. to analyse the pipe statics.
Facing the choice!
On the market, a lot of different products are offered to manage maintenance and repair of GRP-, concrete and fibre cement pipes. Coupling systems which are adapted for the requirements mentioned above cope with these tasks. Aside the product features the know-how of the coupling manufacturer is of utmost importance.
Piping network operators taking responsibility for their assets very often opt for pipe cou-plings made by STRAUB Werke AG in Swit-zerland. STRAUB offers a 40-year experience and leading know-how in pipe joining
tech-nology together with numberless worldwide references.
The STRAUB product range offers flexible cou-plings and repair coucou-plings up to an outside diameter of more than 3500mm. Depending on the application type, the products STRAUB-FLEX or STRAUB-OPEN-STRAUB-FLEX can be selected to solve the specific problem. They are manu-factured stepless for any existing diameter and will therefore “fit like a glove”.
The gasket of the STRAUB couplings (Figure 2) provides a pressure-supported sealing
principle, compensates for tolerances and is damping noise, vibration and movement. It en-sures a long-term and leakage-free sealing on any pipe material. STRAUB couplings are opti-mised for their distinct type of use in extensive test-runs at the in-house R&D laboratory. The system pressure (PS) plays an important role for the dimensioning of the coupling.
For example, STRAUB-OPEN-FLEX couplings (Figure 3) can be wrapped around a
dam-aged pipe; this avoids the cutting of the pipe and allows a quick and durable repair. STRAUB-OPEN-FLEX is frequently used to
replace untight REKA-lugs (Figure 4) or to
tighten circular cracks on concrete pipes. As even STRAUB couplings would not solve any existing problem, customised and dedi-cated solutions will be developed if required. In the event of damaged pipe surfaces, an on-site method to achieve a smooth pipe surface was generated in company with the specialty chemical producer SIKA AG.
Sometimes the corrosion resistance of the stainless steel coupling could be an important issue. To select the proper steel grade, the soil would be classified. Based on this classi-fication, the choice is then made between the grades 1.4301 (AISI304) or 1.4571 (AISI316). An anti-corrosion-coating could also be added when necessary.
Fig. 2: Cross section of the STRAUB-FLEX gasket
Fig. 3: Repair realised with STRAUB-OPEN-FLEX
P ho to : S TR AU B W er ke A G P ho to : S TR AU B W er ke A G
Fig. 4: STRAUB-OPEN-FLEX replaces an untight
REKA-coupling
Fig. 5: Connection of a stainless steel reducer with GRP pipes
P ho to : S TR AU B W er ke A G P ho to : S TR AU B W er ke A G
33 3R international · Special-Edition · 2/2008
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Meeting the most stringent of requirements is what we do every day. We focus our full attention on ensuring that you obtain the right solutions for your pipe cou-plings. Your demanding, specialized problems are pre-cisely where you can rely on our long years of experience and expertise: in support and consultancy, handling technical issues, engineering, project supervision and documentation.
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More information from: Straub Werke AG, CH-7323 Wangs, Switzerland www.straub.ch, Tel.: Germany: +49 (0) 621 486 2907
Examples
The below-mentioned practical examples highlight some cases of troubleshooting with STRAUB pipe couplings.
Integration of a stainless steel reduction into a GRP pipe system in an inspection chamber
On the Zurich airport, two GRP pipes of DN 250 and DN 400 had to be connected with a s/s reduction in a chamber. The re-duction should be easily assembled and dis-assembled for inspection purposes, even in the confined space. It was connected to the GRP pipes by using STRAUB-FLEX 2LS/LU couplings (Figure 5) which perfectly met all
the demands.
Installation of a concrete chamber with a cardan joint
If pipe sections or especially chambers are added to a concrete pipe scheme subse-quently, uneven soil compaction often will cause certain ground settlement. In Austria, the extension of a rainwater retention pipe system necessitated the installation of sev-eral manholes. To avoid severe damages a
cardan joint realised each with two STRAUB-FLEX 3LS couplings was chosen to connect the manholes to the existing pipework ( Fig-ure 6).
Adjusting diameter tolerances and ovality
Existing pipework as well as new-laid schemes can give reason to prepare the pipe surfaces
P ho to : S TR AU B W er ke A G Fig. 6: Flexible connection of a concrete pipe and a concrete manhole
at the junction. The pipe wall would either be cylindrically turned or a levelling layer would be applied. In this particular case (Figure 7)
the diameter tolerances and the ovality of a steel pipe DN 3500 had to be equalised before the STRAUB-OPEN-FLEX 3X coupling could
be installed. A special 2-compound filler was therefore developed together with SIKA AG.
Conclusion
The STRAUB product range and the experi-enced STRAUB team offer the solution for main-tenance, replacement, re-installation and repair of GRP-, concrete and fibre cement pipes. According to the complexity of the issue it is absolutely recommended to get in contact with the STRAUB application support team on time.
Literature
[1] TRGS 519: Asbest Abbruch-, Sanierungs- oder Instandhaltungsarbeiten, edition January 2007 [2] Huenerberg, K.: Das Asbestzement-Druckrohr,
Berlin: Springer-Verlag, 1963, p. 4
[3] Huenerberg, K.: Das Asbestzement-Druckrohr, Berlin: Springer-Verlag, 1963, p. 356 et sqq. [4] Z.B. Zweckverband Landeswasserversorgung,
Stuttgart: www.lw-online.de; Zweckverband Bodensee-Wasserversorgung, Stuttgart: www. zvbwv.de
[5] For further information see: www.amex-10.de [6] Haakh, F.: Sanierung einer
Spannbetondruck-leitung DN 1500 mittels HDPE-Inliner, GWF Wasser/Abwasser (2007) No. 5, p. 375 et sqq.
[7] Treiber, J.: LinerGrip connectors for thin walled PE liner, 3R International(2007) Nr. 3, p. 140 et sqq. [8] Baumgartner, F.: Spannbetonrohre und -leitun-gen: ein Erfahrungsbericht, energie|wasser-praxis (2006) No. 7/8, p. 24 et sqq.
Internet sources:
· Homepage of STRAUB Werke AG: www.straub.ch · SIKA specialty chemicals: www.sika.com
Authors:
Sascha Radosevic
STRAUB Werke AG, Wangs, Switzerland
Phone: +41 81 7254173 E-mail: radosevic.sascha@straub.ch
Jan Treiber
FRIATEC AG, Mannheim, Germany
Phone: +49(0)7551/301041 E-mail: jan.treiber@friatec.de
Fig. 7: 2-component filler to level the diameter
tolerances of steel pipes DN 3500
P ho to : S TR AU B W er ke A G
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