Pipe cleaning

The method of the pipe cleaning refers to the activity, or the apparatus for cleaning and maintenance of pipelines . The medium conveyed in the pipes can lead to deposits and finally to partial blockages. In plant construction and industry , special requirements are placed on pipelines with regard to surface roughness or heat transfer . In the food and pharmaceutical industries as well as in medical technology , the requirements are sterility and freedom from foreign substances, for example after installing the pipeline or after a product change. Deposits can also cause corrosion and thus failure of the pipelines.

Depending on the application, the pumped medium and the pipe material, the following methods of pipe cleaning are available:

Lost pipes

Lost pipes are pipes that have to be replaced after a single use. This type does not actually represent a real pipe cleaning and is very often used in the medical field, for example with cannulas of syringes , infusion needles or with medical devices such as the artificial kidney during dialysis . The reasons here are first of all the risk of infection , but also too complex reprocessing, which is out of proportion to the costs of pipe cleaning, especially in the case of low-quality mass products . This technique is only used for pipes with an extremely small diameter of up to approx. 20 mm. For the same reasons, this approach can also be found in the food and pharmaceutical process engineering , where the diameter can also be greater than 20 mm.

Flushing

The simplest pipe cleaning process is a pipe flush. Here, flushing outlets or hydrants in the drinking water network are often used. Most loose deposits are removed by simply increasing the flow rate. Nowadays, various flushing methods are used in drinking water and drainage pipes, for example:

Water flush
Air-water flush
Air-water impulse flushing
Suction rinse
Solids flushing
Suction cup .

Chemical pipe cleaning

Cross-section of a pipeline narrowed by scaling

Chemical pipe cleaning means the use of cleaning fluids or chemicals to remove the deposits. Typical examples are removing a blockage with a pipe cleaner or decalcifying a coffee machine . In the latter case, the scale is removed using citric or acetic acid . Depending on the area of application and the material of the pipe, special cleaning fluids can be used, including multi-stage treatment:

chemical activation
cleaning
do the washing up

make necessary. This type of cleaning sometimes necessitates a shutdown of the respective system and then leads to downtimes that are often undesirable. For continuous production it is then necessary to install these systems multiple times ( redundantly ). Another disadvantage is that in the industrial area ( reactor , heat exchanger , condenser, etc.) just as large amounts of cleaning fluids occur, which can lead to disposal difficulties. Another problem arises in the food industry due to the possible toxicity of the cleaning fluids. This can only be remedied by strict adherence to the flushing regulations and precise control of residual quantities. This requires complex verification procedures. Overall, the process of chemical pipe cleaning can be used for any diameter, but the volume of a pipeline will result in practical application limits.

Mechanical pipe cleaning

The mechanical pipe cleaning system is a cleaning body that is moved through the pipe to remove deposits on the pipe wall. In the simplest case, it is a corresponding brush that is moved back and forth in the pipe by means of a rod or a flexible spring (spiral spring: pipe cleaning spiral ). However, several different processes have developed in the large-scale and industrial sectors.

Offline procedure

Functional principle of pipe cleaning with pigging technology

Example of a condenser cleaning system using the online process

Brush for pipe cleaning

The offline processes are characterized by the fact that the system to be cleaned must be taken out of operation for the pipe cleaning in order to start the cleaning body or bodies and carry out the cleaning process. With these methods, one still has to distinguish between passive and active cleaning bodies.

The passive cleaning bodies can be brushes or special constructions such as pigs (but also see below) that are moved through the pipes by means of compressed air , water or some other conveying medium. Mostly, the cleaning is done by the oversize of the cleaning body compared to the pipe inside diameter. The types range from brushes with bristles made of plastic or steel , scrapers for smaller pipe diameters to complex designs with built-in spray nozzles for pipelines. This method is used in the nominal width range from approx. 5 mm up to several meters. The cleaning of clogged drainage pipes of domestic sewage pipes with a rotating flexible shaft (pipe cleaning spiral) also falls into the same area .

The active cleaning bodies, also called internal pipe manipulators , are more or less remotely controlled robots that move through the pipes, pulling cables for power supply and communication as well as hose lines for the cleaning fluid, and perform the cleaning task. Here are measuring instruments or cameras carried to monitor the function. So far, such devices still required a minimum diameter of around 300 mm, but work is being done on a further reduction. The maximum useful diameter for these devices can be specified as around 2 m, since from this diameter onwards, inspection of the pipeline is definitely more cost-effective. In this diameter range, the robots can only be used for chemicals that are harmful to health.

Online procedure

In the on-line process, the cleaning body moves with the conveying medium through the pipes and cleans them due to its oversize compared to the pipe inside diameter. These cleaning bodies are sponge rubber balls in the diameter range up to about 50 mm , in larger nominal width ranges up to oil pipelines pigs . Sponge rubber balls are mainly used for cooling water such as sea , river or cooling tower water. Adapted cleaning bodies are conceivable for the chemical or pharmaceutical industry; however, the media flows are so low here that offline processes are mostly used. Since the cleaning bodies must not remain in the conveyed medium, they must be separated again after the pipe has passed through. In the case of sponge rubber balls, this is done through special sieve devices ; in the case of pigs, a discharge station (so-called “pig trap”) is installed. The sponge rubber balls are then fed back in front of the system to be cleaned using a corresponding ball return using the Taprogge method ; the pig is usually removed by hand and fed back into another feeder. While the sponge rubber balls ensure continuous cleaning, the pig system is discontinuous.

Thermal pipe cleaning

With thermal pipe cleaning, the covering is dried by heating , whereby it falls off due to its brittleness and is then transported away either by the conveying medium or a flushing liquid. The heating can, depending on the required temperature, be pipe heating or induction heating . This process is an off-line process. Occasionally, it is also used to sterilize the pipeline in the pharmaceutical or food processing industry. A diameter range cannot be specified here, as this method can only be used for certain processes and the technical limitation of the heating is only given by the materials and the required amount of heat .

Special forms

Special forms of pipe cleaning are all those processes, some of which are only at the experimental stage and do not come under the processes listed above, such as:

Induction of pressure surges so that the covering becomes detached due to the short-term material expansion. In groundwater wells, the impurities are occasionally loosened with the help of detonating cords and then water is pumped out until it is clear again;

Use of vibrations, partly on the pipes by means of vibration exciters, partly by means of piezo crystals in the conveying medium, in order to turn the conveying medium into a cleaning medium by reducing the surface tension ;

Magnetic fields to prevent pipe calcification (effectiveness is strongly doubted);

Nanotechnical treatment of pipe surfaces to prevent deposits.

literature

W. Krass, A. Kittel, A. Uhde (Ed.): Pipeline technology - mineral oil pipelines, TÜV handbooks Volume 3 . TÜV Rheinland Verlag, Cologne 1979, ISBN 3-921059-32-1 .
E. Böhler, D. Hofmann, J. Tränckner: Publications from the Technologiezentrum Wasser Karlsruhe Volume 27: Flushing of water supply networks to avoid rust water formation . DVGW Water Technology Center Karlsruhe (TZW), Karlsruhe 2004, ISSN 1434-5765 .