HOBAS PIPES AS A TOKEN OF RESPECT FOR THE ENVIRONMENT: GUARANTY FOR THE REDUCTION OF WATER LOSS AND ENERGY CONSUMPTION IN WATER SUPPLY NETWORKS

Gheorghe Dabu
General Manager, HOBAS GROUP

INTRODUCTION

The Hobas Group has, during the past 30 years, grown into a major producer of GRP (glass-reinforced polyester) pipes with currently 20 manufacturing plants and about 80 percent of the world market of GRP pipes for municipality applications.

In October 1994, Hobas Group opened its offices in Bucharest.

The new company, HOBAS TUB ROMANIA S.A., was registered on June 26, 1997 and the official opening was on December 8, 1998.

In the Romanian factory, pipes and fittings are produced from DN 300 mm to DN 1200 mm, PN 1 – 16 bar, SN 5000 – 10.000 N/sq.m, as well as manholes. The products have received the Technical Authorisation no. 016-05/865-1999 from the Ministry of public works and Land Planning.

At present, HOBAS pipes are being used in Romania in water supply works and sewerage in: Fagaras (16 km), Dragasani (55 km), Cluj (29 km), Petrosani (14 km), Constanta (5 km), Arad (5 km), Focsani (4 km), Brasov (12 km), Câmpina ( 4 km) and others.

The growth of GRP as a pipe material is logical. It is a very corrosion resistant material and it is a composite material that can be therefore engineered to suit any application. From the early design trials of GRP pipes, the material has been growing in one of the most researched on the market with very safe static calculation methods and manufacturing standards, having as a priority the safety of the environment.

The steps further in computer technology have enabled manufacturing processes to be developed which give a precise control of the raw material distribution within the pipe wall. Manufacturers of Hobas pipes are today major purchasers of raw materials and the volume has made it interesting for the raw material suppliers to develop resins and glass suitable for pipes. The raw materials considered as the most suitable 15 years ago are no longer adequate now.

PIPE WALL BUILD UP

The wall of a Hobas pipe is built up with 14 layers, which can be varied to suit every individual application. The raw material is fed into a rotating mould and when the feeding process is completed, the mould spins at a high speed and the pipe wall is completely de-aired and void free from a centrifugal force up to 80 bar. The pipe wall is polymerised as a “solid block”. In the manufacturing process the glass distribution is very well controlled and, with the combination of the cutter and the mould speed, the direction of the fibres can be controlled according to whether high hoop or axial strength is required. Each of the 14 layers has a specific function within the pipe wall. From the interior, there is a flexible layer (liner) without any glass content. This liner is minimum 1 mm thick and ensures very good hydraulic properties of the pipe and a very high abrasion resistance. Behind the liner, there are two barrier layers with a glass content gradually increasing from 0 to 40 percent. The liner and the barrier layers together ensure that no media or gases can penetrate into the structural layers of the pipe.

Behind the barrier layers are ten structural layers, which are varied according to whether it is a pressure or non-pressure pipe and according to the required stiffness class. The final, outer layer is a scratch resistant layer, which makes the pipe easier to handle during installation. The layer also prevents UV radiation penetration into the pipe wall.

PIPE DESIGN

Standards for plastic products are formulated on the assumption that the materials creep when they are subjected to stress and this results in a change of properties with time. Product design is usually based on the projected values of the material strength after 50 years and, in order to determine these values, long term testing as well as practical experience is used. In strain corrosion tests, Hobas pipes show the same regression curve in pH 7 as in pH 1. The acid does not influence the results. In cyclic loading tests, the burst pressure of the pipes are not changed after a pipe has been subjected to I million load cycles of +- 25 % of the PN. We design pressure pipes with a minimum initial burst pressure of 4 times the PN and we know that this gives a safety factor of 2 against internal pressure after 50 years of service. Creep in a plastic material is predictable and it is a design factor. Corrosion in metals is not always predictable.

There are many routine tests done on both raw materials and on the finished product. It is sometimes discussed whether it is necessary to pressure-test a Hobas pipe as required by the current British Standards. Pressure testing of a pipe at up to twice the working pressure gives very little information as the pipe is designed for a burst at four times the working pressure. Burst testing is a more reliable method and the pressure-test requirements of each pipe are not included in the new CEN and ISO standards.

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