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Asbestos-Cement Pipe: A Special Report
A/C pipe is used in a variety of applications. A/C pressure pipe is used primarily for the distribution of potable water, as well as for sewer force mains and industrial effluent and process piping. A/C non-pressure pipe is used for sanitary and storm drainage systems, casings for electric cables and for duct work. In all critical parameters, the evidence weighs heavily in favor of asbestos-cement over competitive products such as polyvinyl chloride (PVC) and ductile iron (DI).
There are a number of factors to consider in evaluating the costs of various pressure pipe . The end price of the pipe is only one component of a thorough cost comparison. In order to make an informed judgement regarding the long term economic feasibility of a pipe, the user must consider the building and equipment costs involved, the availability and price stability of raw materials, labor costs, manufacturing costs, installation and operating costs, as well as the durability of the product. The following analysis demonstrates the significant, long term cost advantage of A/C pipe.
Lower Building and Equipment Costs
The fairly simple manufacturing process for A/C pipe translates into lower costs for building and start-up. The equipment, either new or used, is easily accessible and frequently available locally.
Ductile Iron (DI) requires the greatest capital outlay because of the large building and complex equipment it requires. Traditionally, the construction of a PVC pipe plant has required the lowest capital outlay, however problems with quality control have resulted in the need to install costly and sophisticated computer systems. If this trend continues, PVC building and equipment costs will soon surpass those of A/C pipe.
Raw Materials: availability and price stability
The price of portland cement , the main ingredient in A/C pipe, has remained relatively stable over the years. A highly competitive market has ensured that price increases have been minimal. Moreover, portland cement is almost always available locally from more than one source. The price of asbestos has also remained relatively stable, but fluctuations in its price have less of an impact on final costs because it comprises no more than 15% to 20% of the raw materials used.
DI pipe is highly dependent on the price of scrap iron which has fluctuated appreciably. In addition , the type of scrap iron required is not always available locally in sufficient quantities and must be imported. International trade restrictions often make this process both difficult and costly. Cost variations of process additives such as magnesium alloy and ferrosilicon must also be factored into the final price.
Approximately 75% of the material cost of PVC pipe is attributable to PVC resin, and as such, its final cost is highly sensitive to fluctuations in the price of resin. The price of PVC resin, a petrochemical product , is closely linked to international oil prices which have been anything but stable. Other additives, equally dependent on petrochemical prices and supply conditions are also an important part of the product’s cost structure. In addition, recent attempts to replace potentially dangerous lead compounds used as stabilizers in the manufacturing process have resulted in increased costs and pipe failures.
A/C Production Creates Jobs and Saves Energy
In terms of the manufacturing costs of pipe , the principal factors to consider are the costs and availability of labor, and the energy demands of the process.
Although A/C pipe has a larger labor component than DI or PVC, for the most part the workers do not require specialized knowledge or expensive training. This can be an important factor in local job creation, particularly in developing countries. In contrast, both DI and PVC pipe production require highly trained workers to manage the specialized demands of their manufacturing processes. Frequently, complex manufacturing processes require importing expertise from outside the community or even outside the country.
The other major advantage of the A/C manufacturing process is that it requires considerably less energy than either PVC or DI production. A/C pipe uses about 20% of the energy required for the production of DI pipe and about 40% of that for PVC pipe. The cost of A/C pipe is therefore much less dependent on both the price and availability of local energy supplies. This factor contributes to lower volatility and general cost-savings for A/C pipe production.
A final factor to consider in a comparison of the manufacturing costs of A/C , DI and PVC pipe is the cost of finishing and protection. Of particular concern is the cost of anti-corrosion protection for DI. Both zinc coating and polyethylene sleeving can add substantially to the installed cost of DI pipe.
Ease of Installation
Installation costs may make up a large percentage of the overall cost of a water system. The ease of installation is almost as important to total costs as the value of the pipe alone. For this reason, the relative ease of installing a/c pipe has become a significant factor. Manufacturers of A/C pipe provide contractors with comprehensive work practices to be followed when pipe is altered during installation. In addition, manufacturers have recently developed special closure lengths and closure couplings which essentially eliminate any field cutting of A/C pipe. The resulting decrease in installation time and the elimination of cutting tools has also reduced labor and equipment costs.
Although DI pipe is fairly robust, its corrosion protection is frequently not. Cracks in an anti-corrosion liner can lead to premature failure. As such, considerable care must be taken during installation. The additional care needed for DI pipe installation , particularly in the diameter range above 12" (300 mm), where these pipes normally compete eliminates the price advantage of DI over A/C pipe in the 18"-24" (450-600 mm) range.
PVC’s light weight makes it cheaper to transport than either DI or A/C pipe. However, this cost advantage can be lost due to the increased handling care it requires. PVC is extremely sensitive to surface damage such as scratches and notching.This makes it more vulnerable to the minor damage which can lead to catastrophic early failures. In addition, PVC is damaged by UV radiation and should not be stored without cover or used above ground unless suitably protected.
PVC pipe also has a higher coefficient of thermal expansion than other pipe, which leads to snaking if not compensated for during installation. It is not suited for high pressures or applications where high traffic or impact loads are expected. Similarly, PVC pipe tolerates only low levels of pressure surges. Under pulsating shocks, it develops fatigue and cracks or yields, depending on the temperature.
Durability Means Lower Operating Costs
The principal criteria to consider are pumping costs, maintenance and durability (replacement costs). Pumping costs are, to a large extent , determined by the interior smoothness of the pipe. A smoother surface results in less resistance and lower pumping costs. For both A/C and DI, the inner smoothness depends on the type of protective coating, if any is used. Over the long term, corrosion in DI pipe can severely affect pumping costs.
It is true that when aggressive water or soil are not involved, ductile iron or cast iron have have performed without major corrosion problems - however, where aggressive conditions exist, severe problems occur frequently and have a significant impact on pumping and maintenance costs as well as durability. In general, A/C is more resistant to aggressive soils and waters, although certain acidic conditions do require additional corrosion protection.
Although operating costs for PVC are initially lower than those of both A/C and DI pipe due to its smoothness, this picture can change quickly. Mechanical failures resulting from material flaws which are easily introduced during production and installation can be catastrophic. Because of the brittle nature of PVC these failures can result in a pipe break rather than a leak.
Overall, the predicted lifespan of PVC is about 50 years. A/C and DI pipe are both expected to last for 70 years. The lifecycle of DI can be much shorter if corrosion becomes a factor. Similarly, that of PVC can be significantly reduced as a result of poor manufacturing quality or damage during installation.
Asbestos-Cement Pipe: The Logical Alternative
Using A/C pipe makes sound economic sense: its raw materials are easily available and stable in price; it creates more jobs for the local economy; it is energy efficient; relatively inexpensive to manufacture and install ; and most importantly it is dependable and durable.
"... I would like to confirm the position of the Organization concerning the use of such pipes for drinking-water supply. Research findings up to date are too inconclusive to demonstrate a health effect from ingested asbestos fibres via drinking water. Consequently, we consider it appropriate to continue the use of such pipes for water supply networks. Their use is particularly important in the case of developing countries where they constitute an economical construction material for supply networks. "
Dr. R Helmer, WHO, Division of Environmental Health
A/C Pipe is SAFE
The selection of the type of pipe to be used in water distribution, sewage or irrigation systems should be based not only on economic considerations, but also on health and safety factors. The previous analysis has shown that A/C pipe has a distinct economic advantage over competitive products. In terms of health risks, a large body of experimental and epidemiological evidence confirms that A/C pipe can be used safely.
The potential health effects of asbestos fibres in drinking water have received much attention. There has been some concern that populations exposed to high concentrations of asbestos in their drinking water over long periods of time would show increased incidence of gastrointestinal tract cancers. Asbestos often occurs naturally in drinking water, and concentrations of several million fibres per litre are not uncommon. The normal use of asbestos-cement pipe contributes relatively low levels of fibres to the water which is conveyed through them.
The World Health Organization (WHO) has been carefully monitoring both epidemiological and animal studies and has come to the following conclusions in a report which it released in 1991: "A study of cancer incidence in Connecticut, USA, over a period of 35 years failed to show a relationship between the use of asbestos-cement pipe and the incidence of gastrointestinal cancer. A further study... published in 1980 also found negative results. There is also no conclusive evidence from animal toxicological studies to date that ingested asbestos is carcinogenic (despite the frequent use of high doses). In addition, epidemiological studies conducted to date provide little evidence of an association between asbestos in public water supplies and cancer."
According to the WHO, asbestos fibres are too large to be absorbed during the digestive process; thus the probability of significant transmission of asbestos fibres would appear to be at most, exceedingly low. All evidence suggests that modern day high density asbestos-cement products pose no detectable risk to the public. Asbestos fibres are carcinogenic only when inhaled, not ingested.
In terms of exposure risks to workers in the chrysotile asbestos mining and manufacturing industries, great progress has been made over the last 20 years. Current exposure levels in Western Europe have dropped from more than 20f/cc to less than 1 f/cc. In many developing countries dust control has improved to the point that exposures are now at minimal levels. This is the case in many A/C plants in India, Nigeria, South Korea, Malaysia, etc... In addition, a recent study which evaluated more than 11, 000 chrysotile asbestos miners born between 1891 and and 1926, concluded that at exposures of less than 50 f/cc no excess lung cancers were observed. Thus, "at current occupational exposure levels, any deaths from asbestosis or lung cancer are most unlikely."
Substitutes can pose greater health risks
There is growing concern in the medical and scientific communities regarding the health and safety risks of non- asbestos pressure pipe . During the Court proceedings which rejected a ban of asbestos in the U.S., the Environmental Protection Agency (EPA) admitted that vinyl chloride monomer (VCM), used in PVC, is a well known human carcinogen that causes angiosarcoma of the liver and possible brain cancer. VCM is known to leach out of the pipe and into the drinking water. Furthermore, PVC pipe in developing areas contains lead as a stabilizing agent.
In separate proceedings, the EPA has estimated the cancer risk from PVC plants to be as high as 26 deaths per year, far in excess of the risks of asbestos. Moreover, " while there is no evidence showing that ingested asbestos is a health risk, the EPA’s own studies show that ingested vinyl chloride is a significant cancer risk that could cause up to 260 cancer deaths over the next 13 years." (21) In terms of the risks of ductile iron (DI), the EPA raised serious concerns regarding the population cancer risk for the production of DI pipe.
Citing these and other reasons, the U.S. Court of Appeals overthrew the ban of A/C pipe in that country for the simple reason that it "actually may increase the risk of injury that Americans face".
"The acute shortage of decent shelter, pipe borne potable water, effective drainage and waste disposal system and irrigation facilities for reasonable large scale farming in developing countries make the use of asbestos cement products a compelling choice for these nations."
Dr. N.A. Okere, Medical Consultant, Nigeria
Many developing nations are in the process of building and expanding their water distribution and sewerage networks. This process is critical to the health and basic quality of life of the citizens of these countries. The challenge imposed by the limited financial resources of many of these countries is in developing programs which have the greatest impact for the greatest number of people. In terms of water distribution, irrigation and sewerage, a system which is less expensive and more durable means that limited financial resources can be used to provide services to other areas or be applied towards other important health programs.
A/C pipe is both more durable and less expensive than competitive products. As the previous analysis demonstrated, in almost all diameters of pressure pipe the total costs of A/C pipe are significantly lower. When the costs of maintenance, anti-corrosion protection, repair and replacement are factored in, A/C has a net advantage in all diameters. Consequently, using A/C pipe means that for the same financial outlay, services can be provided to a greater proportion of the population. Given that access to clean water can result in lower infant mortality and adult morbidity, the choice of A/C pipe is that much more compelling. The control of food and water-borne diseases such as cholera can only be achieved through better environmental sanitation, primarily by constructing safe drinking water and sewage disposal systems.
Efforts to substitute asbestos in cement pipe compounds with Man-Made Mineral Fibres (MMMF) or locally available non-mineral fibres such coconut, sugar cane, cassava and pulp have not met with much success. Non- mineral fibres are unable to withstand the heat or pressure of the cement pipe manufacturing process, nor have they met the desired quality standards. Moreover, they are frequently not available in sustainable commercial quantities without serious negative effects on other sectors of the economy or the environment.
In addition to serious technical drawbacks, the use of MMMF can increase production costs by more than 50%, all in foreign currency. There are also mounting concerns regarding the health risks of many of these fibres, some of which are categorized as Class II carcinogens. For the most part they require the same dust control measures and industrial hygiene practices as asbestos.
Source: WHO, Intersectoral Action for Health, Geneva, 1986
Another important benefit of A/C pipe to developing nations is that it creates local jobs. Unlike other pipe manufacturing operations the construction of A/C pipe does not require a large, highly trained labor force often imported from outside the country. Most positions can be filled by local residents with only basic job training. The spin-off can often give the regional economy a much needed boost. In addition, the equipment required for the manufacture of A|C pipe and the maintenance of proper dust control is very simple and often available locally, both new and used. There is no need to import and service complex machinery from abroad. This also benefits local economies and saves important foreign currency reserves.
In addition to the economic benefits of A/C pipe, numerous studies and case histories have shown that it is possible to use asbestos safely in both industrialized and developing nations. If properly controlled and used, chrysotile asbestos does not pose any significant risk to public or worker health. Over the last 20 years, the chrysotile asbestos mining and manufacturing industries have made great progress in industrial hygiene. In many developing countries such as Nigeria and India, dust levels have been brought to under 1 f/cc, some 50 times lower than the level now believed to result in chrysotile asbestos related cancers.
Although it is true that this is not the case in all countries nor in all plants, but with responsible action by governments, local enterprise, unions and with the guidance of international organizations such as the International Labor Organization (ILO) and the Asbestos Institute, it is possible for developing nations to meet or surpass Western industrial hygiene standards. The continued controlled-use of asbestos fibres will enable developing nations to use their scarce resources to provide basic amenities to larger numbers of people.
A/C pipe is manufactured by the Hatchek/Mazza process from an intimately mixed aqueous slurry of portland cement (80-85%) and a mixture of relatively long and medium grade chrysotile asbestos fibres (15-20%). The slurry is dewatered by a machine using a rotary sieve cylinder and a continuous felt to produce a very thin layer of asbestos cement which is wrapped around a mandrel under pressure until a pipe with the desired wall thickness is produced. The mandrel is then extracted and the pipe is cured by passing through a tunnel-like low temperature oven followed by immersion in or spraying with water, or by autoclaving. After curing, the ends of the pipe lengths are cut and finished to receive couplings that are produced by cutting larger diameter pipe into sections.
A/C pipe is manufactured under carefully controlled conditions in order to achieve a smooth internal finish. The incapsulated asbestos fibres act as a reinforcing material to form an intrinsic part of the cement matrix.
Providing a safe working environment
The effective control of chrysotile asbestos dust in the work place can eliminate health risks to workers. In the manufacture of asbestos cement products most of the processes are "bound-in" or wet. When the asbestos is present in a slurry (a wet mixture) there is no possibility of dust emission. Such processes require only relatively simple safe work practices often referred to as "housekeeping". These include: wetting of the process where applicable; immediate and proper clean-up of waste generated by the process; vacuuming or wet removal of all dust particles generated; and avoiding practices such as dry sweeping which generate dust. These dust control techniques are well known, easily available and require relatively inexpensive and unsophisticated equipment. The capital and operating costs of these methods consist of only a small fraction of the total costs of the plant.
Dust emissions from other components of the manufacturing process can also be easily controlled. The use of enclosed debagging stations as asbestos is introduced into the process and suction hoods during the cutting and finishing of A/C pipe ensure that airborne particles are captured and contained. Much of the waste collected during the production or housekeeping process can then be reintroduced into the the system, thus avoiding environmental pollution and saving on raw material costs.
Frequent monitoring of the work place environment and periodical medical assessments of the workers will verify that the techniques in place are effective. The implementation of a dust control program can produce highly effective results using only the most basic of techniques. Processes such as wetting and vacuuming can dramatically decrease dust levels in plants which may previously have had ineffective or minimal controls. The implementation of local exhaust ventilation and filtration systems will further lower dust levels.
Drain Waste Vent Pipe (DWV) is non-pressure pipe which utilizes a gravity flow process. It is used for sanitary and storm drainage systems, casings for electric cables and for duct work. The most common types of non- pressure pipe are asbestos cement, concrete, plastic, cast iron, steel, copper and brass. The following are some of the advantages of A/C non-pressure pipe over competitive products.
Source: W. Denault & Associates, Paper presented at the International Conference on Asbestos Products, Kuala Lumpur, Malaysia, 1991.<< Retour à l'index des publications
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