Cleaning of industrial pipes - Chemical pipe rehabilitation

Jun 23, 2006

In pipelines in industries formation of deposits occurs frequently. These deposits prevent the transport of substances and need to be removed on a regular basis to ensure smooth operation. Many a times, aggregates are installed such as heat exchangers, cooling tower or chill rolls, mastication rollers, injection moulding machines, bioreactors etc., and they have to function smoothly, because production depends directly on them. There are different processes for cleaning pipes, which include mechanical processes such as high-pressure cleaning, scrapper cleaning or milling, or alternatively chemical and chemo-mechanical processes respectively.

The process with which such pipelines can be cleaned fast and cost-effectively using a chemical purging liquid in situ, in other words, without dismantling and reinstallation and extensive setup time, is described below. The requirements for efficient rehabilitation media, pre-planning and the course of such service are also presented.
Fundamentals
The role of pipelines in industries is to ensure the transport of liquid media for energy, cooling or process water supply or for the preparation of basic production material. In such pipeline systems, deposits build up frequently. Please note: Corrosion effects of the pipe material itself and the formation of incrustation associated with it are not the subject matter of this article but rather a special topic on its own. The present state of technology prevents or limits the formation of deposits if possible, by using inhibitors and biocides. If this is also successful in practice, pipe cleaning becomes unnecessary, or it will possibly only be necessary after several years.
This article focuses on the cases in which either the transporting medium deposits something from itself (e.g. lime in supply pipelines from a lime slurry dosing, such as in flue gas washing). This means that the deposits build up using ions of the transported medium. The other cases are those in which deposit-forming substances from the environment are brought in inevitably because the pipeline system is an open or partially open system.

This could be the case for ex., during the supply of cooling water, if due to high throughput quantities a closed cycle with conditioning were to be implemented without or only with considerable maintenance costs. The most familiar cases are the penetration of dust, pollen, sands etc. The possibilities mentioned above can also occur by all means in combination: There are almost always mixed deposit formations.

If deposits then form, one needs to note that with increasing layer thickness of the deposits, the open pipe cross-section areas (for fluid passage) reduce quadratically. This means for ex. that in a relatively small cooling water pipe (Take for example cooling water supply of injection moulding machines) with diameter of two inches, a deposit size of one centimetre reduces the open pipe cross-section area to only 25 percent.
The generally known Law of Physics (Flow Law and/or Continuity Equation, Bernoullian Equation) states primarily that: If the flow rate for supplying the systems is to be maintained, the flow velocity and consequently the pressure of the supply pumps have to be increased. This means that: The supply pumps have to run with higher capacity which costs more electricity and as a result more money.

Furthermore, the Hagen-Poiseulle Law shows that increase and/or restoration, of a given or desired flow cannot be achieved primarily through increase in pressure but by increasing the pipe diameter. If one considers only the factors such as the kinematic viscosity of a liquid medium and Reynold’s Principle of Similarity, then it becomes apparent that there is nothing more important than open pipes in order to run the systems safely and cost-efficiently.

There will be no explicit description of the above-mentioned laws in form of formula at this point but reference is made to relevant technical literature on fluid mechanics.
In addition to that, there is the danger of clogging/ alkalinisation of the pipelines with increasing deposit thickness within the pipeline. Under certain circumstances this can possibly lead to production failure/breakdown.

Problems and possibilities
Regardless of the above-mentioned fact that the deposits almost always represent a combination of precipitation and corrosion products from the medium on the one hand and substances brought in from the environment on the other hand, one can distinguish between roughly three groups and hence three problems:
Calcification:
Inorganic film which can normally be fully released with chemical products and can be found in carbonate, sometimes also in combination with hydroxide sludges from iron (CaCo3, Fe (OH)3).

Sludge Accumulation:
Inorganic and / or organic film made up of sand (Silicate), which is normally not released but dispersed in order to subsequently mobilise or distribute it. The organic films mostly come from pollen and falling leaves of surrounding trees and are partially oxidatively decomposable.

Biological Films:
This means the formation of an adherent slimy film or growth that stems from the colonization of the inside pipe area by microorganisms. If the colonization becomes prevalent, an initially relatively thin and solid biological film develops like an explosion into a thick growth that can release particles which then cause clogging in filters or at points with minimal pipe cross-section. Another big problem lies in the contamination of plant staff with harmful pathogene germs such as in microbially-induced corrosion.
Chemical cleaning media requirements
The chemical rehabilitation fluids used must meet a whole series of requirements. They are mostly based on organic and inorganic acids.

It must be noted however that the former often shows a very low effect. As a result, they appear to be safe and easy to use but they do not remove the deposits and as such do not solve the problem.

Inorganic acids however often react too vehemently and it leads to severe gas formation as well as fast and uncontrollable full reaction. The removal effect is often minimal. When using unsafe or insufficiently safe inhibited hydrochloric acid, pitting corrosion occurs due to chloride attack in stainless steel pipes, especially on welded joints.

For these reasons, CARELA® is making special rehabilitation products that contain the appropriate inhibitors, stabilisers and wetting agents. They are being developed with respect to the heterogeneous mixture of materials typical in industrial pipelines nowadays and they provide high removal rates in connection with safe handling and a defined disposal route.
Good degassing properties are also necessary so that too much air/mixture of solution does not build up. The rehabilitation agent should act primarily on the surfaces if possible, and mix continuously and thoroughly in the process. With a foam phase floating on the top; this can no longer be ensured in a sufficient manner. In addition to that persistant foarm increases the required rehabilitation agent quantitaly up to twice as much.

This can lead to problems with the handling of the liquid mass. Apart from that it is difficult to drain off foam mass with layer that is half a metre thick. It goes without saying that a good rehabilitation product should be economical to use and it should be cheap.
Procedure and project planning
a) Consultation
Direct consultation with the subsequent client forms the basis for a proper and professional chemical pipe cleaning recirculation and rehabilitation. It is absolutely necessary to view and examine the local situation because this is where the foundation is laid in order to be able to outline the scope of action. Apart from describing the recirculation and rehabilitation cleaning procedure, extensive data acquisition is also carried out.

This includes sketches, drawings, flow sheets and technical documentation of the plant engineer, if necessary also taking photographs of the plant area concerned (provided) that the circumstances are otherwise very hard to describe) as well as clearing substantial questions with regard to the selection of regenerating agent.

Moreover, the maximum timeframe available and the question whether the ongoing production process will be affected and if necessary, a plant area needs to be stopped, also have to be clarified. It is naturally most favourable if production can continue.
b) Sampling
The extraction of a deposit sample from a pipe to be cleaned is essentially helpful for determining the best rehabilitation procedure. Strictly speaking, it is indispensable. However it is well-known and understandable that it is not possible in specific cases to stop the system in order to acquire a sample. In this case, one needs to fall back on experience to prepare a service offer. It is hereby mentioned explicitly that the temporary halting of operations (including production standstill as the case may be) for the purpose of sampling can pay off in spite of initial apparently heavy amount of work involved.

c) Laboratory examination
In contrast to a laboratory analysis in the normal chemical laboratories, in this case no full quantitative determination of the component elements of the sample is carried out but a series of removal tests on the deposit samples concerned are done.

This includes combining different chemical elements and additives with each another as well as changing the parameters such as temperature, time; motion (Flow velocity, gas formation and coagulation as the case may be, and dispersion or emulsification.

This takes place because a proposition, such as exists in determining an element, for ex., according to the method of Atomic Absorption Spectrometry (AAS), lists the spectrum and the components of the deposit mixture in details, however it hardly gives clear evidence of how good or bad the deposits really dissolve in practice.
If for example the components were examined using AAS, then one arrives at the conclusion "22 % silicon content", and it can be combined with quantitative distribution of other components, including SiO2 as the case may be. Chemically, this connection can only be broken off through a so-called "thermal digestion" which cannot be accomplished on a large-scale. The classical analytics therefore led to the conclusion: Chemical pipe cleaning is out of the question in this case.

SiO2 can actually be distributed in the mixed deposit in such a way that the disintegration of other components takes place relatively easily. As a result, SiO2 is suspended, can be dispersed as the case may be and therefore it can be well distributed. Thus, a chemical pipe cleaning can be very successful.

d) Offer preparation
Based on the data acquired, we prepare a service offer that takes into account all the individual wishes of the client. This includes the lab report with information about the expected total volume of deposits and the anticipated total volume of rehabilitation products necessary. The range and type of technical equipment on-site is based upon it and the number of fitters on-site, in other words, the size of the service team and the possible need for night or weekend work is set taking into consideration the maximum time-frame available. This already ensures a positive coordination between subsequent client and contractor.
e) Implementation
After the arrival of the CARELA® service team on site, the place of operation is first set up. In order to flush the pipeline route concerned, a cycle is created using hoses. Flanges are then joined to the ends of the pipeline route to be flushed. Beginning with a powerful pump, a hose route is laid to the pipe on the pressure surface and flanged, and at the end of the pipeline route, a hose is also transferred back to the pump.

The arrangement is completed with a satisfactorily measured collection tank in which, as the case may be, a sedimentation zone for sludge and sand is included. In such a tank in many cases, simultaneous degassing is also possible such as carbon dioxide. Its importance becomes clear when one demonstrates the fact that, for example, 240 litres of carbon dioxide is released from one kilogramme of lime (quoted as calcium carbonate). In the mobilisation of biological films, slime and fine sand as well, the dispersion aids used must be allowed to rerelease their accumulated gas (mostly oxygen), in which case a possible foam formation must always remain controllable.

Furthermore the necessary devices for monitoring the rehabilitation process are installed. Most of the time, the temperature, pH value and electrical conductivity are suggested as parameters and in some cases, the photometric measurement of selected elements that are components of the deposits.

Afterwards flushing of the pipeline route to be rehabilitated is started and the process is monitored continuously through measurements and if necessary, the rehabilitation is reintensified and a partial flow from recirculation is also extracted at specific periods, and neutralized in a process running parallel to it but separate.

The flushing process continues until the deposits have been removed. Afterwards the entire flushing solution (= Regenerate) is neutralised and discharged.
Disposal issues
Modern rehabilitation media must meet the requirements for problem-free disposal. Naturally, everything can certainly be disposed somehow. It is just a matter of costs.

The operator of an industrial pipeline to be cleaned likes to interpret "easy to dispose" and almost always as discharge into the public sewer network and/or in the runoff ditch. As such, CARELA® rehabilitation media are processed in such a way that it can be done in a safe way and in accordance with the relevant legal norms.

In practice, one draws mostly on the threshold value for the parameter pH value and if necessary, settleable substances. Careful neutralization and as the case may be, foam treatment ensures the rightfulness of the disposal. This means in practice, that the used regenerates can be drained off without reservation after treatment.

In any case the fact is that: The method of disposal must be clearly defined and harmonized. The contractor also takes on this responsibility upon request as delivering service.

Contact

CARELA­ R. Späne GmbHVolker Wöhrmann, Dipl. Chem. Ingenieur

79618 Rheinfelden, Germany

Phone:

+49 (0) 7623/7224-0

Fax:

+49 (0) 7623/7224-88

E-Mail:

export@carela.com

Internet:

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