Rehabilitation and Maintenance of Drains and Sewers / Prof. Dr.-Ing. D. Stein, Dipl.-Ing. R. Stein (2004)

Instationary Investigations

In order to simulate long-term loading, the respective cleaning nozzle is pulled through the 12 m long test section 40 to 60 times with a constant water pressure of 150 bar measured at the HP pump and a constant speed of approximately 4 m/min. This pull-through speed was determined on the basis of evaluation of several applications in practice as well as calculation documentation. In the course of the investigations, 30 l of sand, gravel and stones with a diameter of up to 40 mm as well as a brick were introduced into the pipe. After the end of the investigation, the pipes were taken apart for optical evaluation.

The city of Hamburg has developed its own programme based on the following parameters:

Cleaning nozzle: Bomb nozzle (8 x 2.3 mm jet openings).

Nozzle pressure: min. 100 bar.

Speed: v = 1.0 m/s.

No. of passes: 50 times.

Grain size: 60 % sand (0 - 2 mm), 20 % ballast (up to 20 mm), 20 % granulate ( 0 - 4 mm).

Quantity introduced: 2 times 10 l bucket per flushing pass. Renewal of mixture after each pass.

Camera passes: After completion and after every 10th pass.

Besides the investigations of the reaction of pipes, pipe joints, linings, coatings and similar, to the high pressure water jetting process, it is also necessary to test, for instance, the joints of connections with this method.

Image  Investigating the influence of the HP water jetting on branch connections [Stein96h]

A corresponding testing method was developed for the "Fachvereinigung Betonrohre und Stahlbetonrohre e.V (FBS)" (Institute for Concrete Pipes and Reinforced Concrete Pipes) [Stein96h]. The investigation is carried out on sewage pipes DN 300, at the approach in the springline or between the springline and the crown of the branch connection made by the producer or operator of the system to be investigated. A standard cleaning vehicle in which a maximum water pressure of 210 bar can be generated for the flushing investigation is utilised (Image The cleaning nozzle used has 10 openings each with a 2 mm jet diameter and a jet angle of 45°. The water is introduced by means of a 120 m long high pressure water jetting hose with a diameter of 25 mm.

The investigation programme comprises stationary investigation (keeping the cleaning nozzle in one position, e.g. through operational interruption) as well as instationary (long-term loading through many cleanings).

In the stationary investigations, the cleaning nozzle is always kept fixed at the height of the branch connection on the pipe invert. The water jetting pressure is increased from 75 bar in increments of 25 bar to 150 bar. At every step the pressure is maintained for 1 minute. Subsequently a check is carried out by means of optical inspection of the branch connection system.

In order to simulate the long-term loading, the above-mentioned cleaning nozzle is pulled 50 times through the pipe at a speed of 4 m/min at a constant water jetting pressure of 150 bar, measured at the HP pump,. Subsequently, the branch connection is evaluated by optical inspection and quantitatively monitored with the aid of a leaktightness test.

All the above-mentioned investigation programmes ignore the influence of various drive speeds, the number of the jet openings, different jet angles, the type of deposits and their behaviour during the cleaning process as well as the possible effects of the HP water jetting process on sewers that are liable to damage. In the latter case, as a secondary effect and depending on the type of damage and its extent, uncontrolled erosion processes, which inhibit the stability of the pipeline, can be expected in the embedment. No results of investigations are available as regards this problem.

Rehabilitation and Maintenance of Drains and Sewers / Prof. Dr.-Ing. D. Stein, Dipl.-Ing. R. Stein (2004)