The Lifespan of Steel, Clay, Plastic & Composite Pipes
Jan 05, 2022
Steel, clay, plastic and composite pipes range in lifespans, which can be expanded based on maintenance. However, not all are best for every trenchless project.
Selecting the best pipe material for a particular project depends on different factors, but mainly on the purpose of the pipeline. Materials commonly preferred for sewers and culverts are concrete, steel, vitrified clay, polyvinyl chloride (PVC), and high-density polyethylene (HDPE), all of which have their particular desirable characteristics and serviceability. Serviceability is the useful life of a product during which it will perform its intended role to its fullest.
Factors Affecting Serviceability of Buried Pipes
- The factors that cause pipe material degradation or affect its functionality include:
- pH level
- Soil and water resistivity
- Abrasion resistance
- Chloride, sulfate, or acid corrosion
- Fire resistance
- Slow crack growth and oxidation of thermoplastics
- Electrochemical corrosion of steel
The Lifespan of Pipe Materials
The factors mentioned above affect the estimated material service life (EMSL) of a pipe, i.e., the number of years that a pipe or system will provide satisfactory service life before requiring rehabilitation. The most effective way to ensure that a pipe meets the design service life (DSL) is to perform regular maintenance and ensure that flow conditions do not exceed the designed parameters.Practically, design parameters and actual site conditions can vary significantly due to natural and human components such as geology, fluid characteristics, climatic conditions, etc. As the American Concrete Pipe Association points out, predictions regarding durability therefore cannot be made with the same degree of precision as can be made for structural and hydraulic performance. Let’s take a look at the lifespans and characteristics of some preferred pipe materials in the sewer industry.
High-density Polyethylene (HDPE) Pipes (Estimated life span – 50 to 100 years)
HDPE pipes are manufactured by the extrusion technique on a single screw extruder. HDPE granules are melted and cast in dies.
- Fused joints that prevent problems like leakage, and infiltration
- Water-resistant, resistant to corrosion from gasses like hydrogen sulfide
- Abrasion-resistant, and prevents the growth of microbes and bacteria due to its smooth inner surface
- Can be used for rehabilitation purposes like slip-lining, pipe bursting, floating pipe, etc. and can be procured in desired lengths thus reducing joints
- Can withstand pressure surges and is suitable for earthquake-prone areas due to its flexibility.
Cannot be used where exposed to direct sunlight due to damage by UV light
- Not resistant to oxidizing acids, chlorinated hydrocarbons, and ketones
- Has high thermal expansion
HDPE pipes need regular maintenance to ensure smooth performance and longevity of pipelines. Maintenance should include testing for unbillable water loss, system efficiency, regular checking for damages in joints, sensors, and controls.
Polyvinyl Chloride (PVC) Pipes(Estimated life span – 50 to 70 years)
PVC pipes are manufactured by compounding PVC resin with stabilizers or plasticizers in a mixer from where it is fed to a double screw extruder fitted with appropriate sized dies. It is then passed through a heated chamber where it takes the desired form.
Resistant to damage by chemicals and corrosion from exposure to harmful gasses
- Can be easily cut into the desired length of segments making it easy to install
- Affordable and easy to maintain.
Supports lesser load compared to GI and CI pipes especially in places with heavy vehicular traffic
- Needs good backfill support to prevent bending of pipe sections
- Can warp or distort under extreme heat
Regular maintenance of PVC pipes should include regular checks for blockages, leaks in joints, and proper support from backfill and surrounding soil to prevent cracking due to stress from top loads.
Reinforced Concrete Pipes (RCP)(Estimated life span – 75 to 100 years)
Correctly installed reinforced concrete pipes can last for a lifetime. These pipes are manufactured using concrete made from cement, fly ash, aggregates, and water. (Read also: Why Reinforced Concrete Pipe is Ideal for Pipejacking.)
Provide an excellent service life compared to other materials
- Not easily breakable and hence can operate under high-pressure conditions
- Does not allow the intrusion of roots or soil
- Are load bearing and thus require bedding only from the spring line to the pipe bottom
Though not easily breakable, handling during installation has to be done with utmost care to prevent damage
- Requires heavy-duty machinery for installation
- Vulnerable to hydrogen sulfide (H2S) attack
- Its rough internal surface leads to a build-up of material.
Concrete pipes need regular maintenance to help prevent build-up from sewage material. Regular inspection for cracks, leakages, and intrusion can prevent corrosion, blockage, and build up thus increasing the service life of the pipe.
Vitrified Clay Pipes (VCP) (Estimated life span – Several centuries)
Vitrified clay pipes are one of the longest-lasting pipe materials. According to Logan Clay Pipe, it maintains the same strength, abrasion resistance and corrosion resistance as the day it was made. VCP is manufactured by blending clay and shale and forming them into pipes which are then vitrified making them waterproof and resistant to chemicals.
- Highly resistant to chemical and acidic erosion
- Cheaper than steel and iron pipes and can be used as a direct jacked pipe for trenchless rehabilitation
- Has the longest lifespan of all currently utilized materials
- Newer versions are sturdier and are less porous with better joint designs
- Has lower-pressure tolerance than metal pipes
- It is brittle and can easily crack and allow intrusion from roots
- Pipe length is limited due to the manufacturing process
Older vitrified pipes need to be replaced with a better alternative as they were not manufactured to standard specifications and can fail under strain.
Galvanized Steel Pipes (Estimated life span – 40 to 70+ years)
Steel pipes are commonly used for water system pipes but can also be used as a casing for sewer pipes. It is a metal alloy with greater strength than iron pipes. The steel pipes are alloys of iron and other metal like aluminum, manganese, etc. and are either seamless or welded along one side of its length. A layer of zinc is applied over the steel pipe to help fight corrosion.
- Have greater durability and flexibility than iron, resulting in bending rather than breaking
- It is resistant to build up and corrosion under proper maintenance.
- It has a higher cost of purchase and installation
- Expensive and subject to corrosion but at a slower rate than iron pipes
- Needs coatings for chemical resistance
- Heavy to handle
Over time these pipes can develop flow blockages from mineral deposits inside the pipe. Regular maintenance checks can help prevent build-up and extend the serviceable life of the pipe.
There are many different materials that are used for the purpose of sewer and water pipeline installations. Above are just a few and the most commonly used materials. With the advent of trenchless technology, it has become easier to replace or repair pipelines that are old or have been damaged. Materials like HDPE are favored for trenchless rehabilitation because they are resistant to corrosion and are adaptable to different situations. Maintenance of pipelines is the key to ensure longer and trouble-free service life irrespective of the material of the pipe. Selecting the best pipe material for a particular project depends on different factors, but mainly on the purpose of the pipeline. Materials commonly preferred for sewers and culverts are concrete, steel, vitrified clay, polyvinyl chloride (PVC), and high-density polyethylene (HDPE), all of which have their particular desirable characteristics and serviceability. Serviceability is the useful life of a product during which it will perform its intended role to its fullest.
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