| Performance metrics | Hot dip plastic steel pipe | Galvanized steel pipe |
| Compressive strength | ≥350MPa | 235MPa |
| Corrosion resistance life | 50 years | 15-20 years |
| Connection method | Flanges/Welding/Threads | Only welding |
Major engineering applications
Hong Kong Zhuhai Macau Bridge: DN400 impregnated steel pipes are used for the sea crossing section, with a design lifespan of 120 years
Ultra high voltage project: protective casing for 1000kV Huaihe River crossing section
Industry development trend:
Intelligent pipeline: MPP pipe with built-in fiber optic sensor for real-time monitoring of cable status
Environmentally friendly material: Bio based polylactic acid (PLA) power pipe enters the experimental stage
Structural innovation: 3D printing honeycomb structure pipeline improves unit strength ratio
Both ring stiffness and ring flexibility are important indicators of plastic buried drainage pipes. The difference between the two lies in"stiffness"and"flexibility". However, many people are ambiguous about the specific differences between the two. Here is a comprehensive comparison between the two.
1、 Concept
● Ring stiffness:
Ring stiffness refers to the ability of a pipeline to resist circumferential deformation, mainly measuring the stability of the pipeline under external loads such as soil pressure and vehicle loads. The higher the value, the stronger the structural ability to resist radial deformation.
In the International System of Units, ring stiffness is usually expressed in kilonewtons per square meter (kN/m ²), and common ring stiffness grades include SN4, SN8, SN12.5, etc.
● Loop flexibility:
Ring Flexibility refers to the bending ability of a pipeline under external forces, reflecting the flexibility characteristics of the pipeline. The stronger the flexibility, the better the pipeline can adapt to external pressure without cracking.
2、 Calculation method
Ring Stiffness:
The calculation formula for ring stiffness includes two types: experimental and theoretical,
The first method is based on the GB 9647-2015 standard:
S=F/ΔY⋅L*k
In this formula: S is the ring stiffness (kN/m ²), F is the load at 5% deformation (kN), Δ Y is the vertical deformation (m), L is the sample length (m), and k is the coefficient (approximately 0.149, adjusted according to standards).
Another type is based on the ISO: 9969 standard,
Expressed as: S=E ⋅ I/D3
Where E is the elastic modulus (Pa), I is the moment of inertia of the cross-section (m ⁴), and D is the outer diameter (m).
Ring Flexibility:
Ring Flexibility does not have a direct calculation formula and is usually evaluated through experiments (according to ISO 13968:2008). In the test, apply radial pressure to a specific deformation (such as diameter compression of 30%), observe whether cracks or yielding occur, and focus on measuring the material's flexibility limit.
3、 What are the influencing factors?
Pipeline material (elastic modulus)
The higher the elastic modulus of the material, the greater the ring stiffness of the pipeline. For example, materials with strong rigidity such as steel and concrete can increase the ring stiffness, while materials with higher elasticity such as plastic pipes are relatively lower.
In contrast to ring stiffness, materials with lower elastic modulus (such as PE, rubber) typically have higher ring flexibility because they are more prone to deformation and restoration, while materials such as steel have stronger rigidity and lower ring flexibility.
● Pipeline structure
Structural wall pipelines (such as HDPE double wall corrugated pipes, steel reinforced spiral corrugated pipes, etc.) are designed with corrugations and reinforcement layers, which not only provide high ring stiffness and can withstand large external loads without excessive deformation, but also have strong ring flexibility, which can adapt to external deformations such as foundation subsidence and external forces, and avoid pipeline rupture.
In contrast, solid wall pipelines (such as PE water supply and drainage pipes) have lower ring stiffness, are prone to significant deformation under high load environments, lack elasticity, have poor ring flexibility, and are easily affected by external deformation, leading to brittle fracture.
● Wall thickness of the pipe
When the thickness of the pipe wall increases, the ring stiffness of the pipeline increases. Thicker pipe walls can improve the compressive strength of the pipeline, but at the same time, it can cause a decrease in the ring flexibility of the pipeline, resulting in a lack of elasticity and a weakened adaptability to external deformation.
4、 Engineering application
● High ring stiffness applicable scenarios
——Deep buried pipelines need to withstand significant overburden pressure and require high structural strength, such as municipal drainage and sewage pipelines.
——Under high load environments such as highways and airports, the load is relatively large and exerts significant pressure on pipelines.
——In non backfilled dense areas, due to insufficient backfill density, the support force around the pipeline is weak, and high ring stiffness pipes can reduce the risk of deformation.
——In industrial fields such as chemical plants and port pipelines, it is necessary to withstand the heavy pressure of mechanical equipment or storage tanks, requiring stable pipeline structures and minimal deformation.
● High ring flexibility applicable scenarios
——In areas with obvious foundation settlement, such as coastal areas and soft foundations, it is necessary to adapt to uneven settlement of the strata and reduce the risk of pipeline fracture or leakage caused by foundation changes.
——Earthquake prone areas require pipelines to withstand significant deformation, avoid rigid fractures, and improve seismic resistance.
——Non excavation construction such as pipe jacking requires pipelines to have a certain degree of flexibility to adapt to terrain changes and reduce stress concentration.
——Irrigation of farmland and water supply pipelines (such as mountainous and hilly areas) in mountainous and hilly areas require pipelines to adapt to the undulating terrain and be easy to construct and lay.
In order to clarify the difference between height change and ring flexibility, the above four points have been summarized. Simply put, ring stiffness is the ability to resist deformation, while ring flexibility is the ability to deform without cracking, both of which are important indicators of plastic buried drainage pipelines.
Industrial pipelines often contain high-temperature and high-pressure steam, as well as flammable, explosive, or toxic gases, due to the complexity of the medium they transport. If colors are used randomly or not clearly labeled, it is very easy to cause misoperation, maintenance misjudgment, and serious consequences. Therefore, it is still valuable to clarify the basic identification colors.
1、 What are the basic identification colors?
According to the current standard for industrial pipeline identification colors, GB 7231-2003"Basic Identification Colors, Identification Symbols, and Safety Signs for Industrial Pipelines"is applicable to non underground gas and liquid transportation pipelines in industrial production.
Basic identification color identification method:
The basic identification color identification method for industrial pipelines should be selected from the following five methods by the user:
a) Mark the entire length of the pipeline;
b) Mark the pipeline with a 150mm wide color ring;
c) Identify the pipeline with rectangular identification color tags;
d) Identify the pipeline with rectangular identification color tags with arrows;
e) Identify the pipeline with a hanging identification color tag.
Note: When using methods b), c), d), and e) mentioned above, the minimum distance between two markings should be 10 meters, and the location of the markings should include the starting point, ending point, intersection point, turning point, valve, and both sides of the wall hole of all pipelines, as well as other parts that need to be marked. The minimum size of the labels for c), d), and e) should be determined by the ability to clearly observe and identify the color.
2、 What is the composition of identification symbols?
(1) Material name
a) The full names of substances, such as nitrogen, sulfuric acid, and methanol. b) Chemical formulas, such as N2, H2SO4, and CH3OH.
(2) Flow direction
1) The flow direction of substances in industrial pipelines is indicated by arrows:
If the flow of substances in the pipeline is bidirectional, it is indicated by a bidirectional arrow
2) When the basic identification color identification method adopts d) and e) mentioned above, the direction of the label is taken as the flow direction of the substance inside the pipeline; If the material flow in the pipeline is bidirectional, the direction of the label should be made bidirectional, as shown in the following figure: (3) Main process parameters
The identification of main process parameters such as pressure, temperature, and flow rate of materials can be determined and adopted by the practical party as needed.
4、 Danger signs
a) Scope of application:
The substances inside the pipeline, which belong to the hazardous chemicals listed in GB13690, should be marked with danger signs on the pipeline.
b) Representation method:
Apply a 150mm wide yellow color on the pipeline, and a 25mm wide black color ring or ribbon on each side of the yellow color. The safety color range should comply with the provisions of GB 2893.
c) Indicate location:
On or near the identification of basic identification colors.
5、 Fire protection signs
The fire-fighting dedicated pipelines set up in industrial production shall comply with the provisions of GB 13495-1992 and be marked with the identification symbol of"fire-fighting dedicated"on the pipelines. The identification location and minimum font should comply with the provisions of 4.5.5.4 in the standard.
A comprehensive list of plastic pipeline raw materials: new materials, recycled materials, secondary materials, and recycled materials. How are they classified?
1、 New materials (raw materials, branded materials)
Definition: Raw polymer particles produced by legitimate petrochemical enterprises (such as Sinopec, PetroChina, etc.) according to product grades and standard parameters, without use or processing, with high purity and the most stable performance.
Source: Main brand products produced by legitimate large-scale petrochemical enterprises, such as Sinopec, PetroChina, Nordic Chemicals, Basel, Dow, LG, etc.
● Performance characteristics: - high purity, stable performance; ——Excellent mechanical properties, processing performance, corrosion resistance, and aging resistance; ——Transparent or natural color; ——Complete Technical Data Sheets (TDS) and certificates of conformity can be provided.
Applicable scenarios: High safety products such as drinking water pipes, gas pipes, hot water pipes, etc; ——Pipelines that require long-term strength (such as MRS) and pressure bearing performance.
2、 Secondary card material
Definition: Non standard products produced by petrochemical plants during the production process due to process deviations, unstable parameters, etc. Although they are new materials, they do not fully meet the technical specifications of the main brand number.
Source: Production of petrochemical plant auxiliary lines, commissioning stage, tail materials, etc. Generally, there are also production batches and numbers, but they cannot be sold as primary materials.
● Performance characteristics: - Belongs to"secondary new materials"; ——The performance is slightly lower than that of the main brand new material, but usually still better than the recycled material; ——The price is cheap, but there may be slight differences in appearance and color; ——There may not be a complete testing report.
Applicable scenarios: Drainage pipes, cable conduits, agricultural pipes, etc. with low performance requirements; ——The mid to low end market that requires cost control.
3、 Return of materials (commonly known in the industry)
Definition: Commonly known as"recycled materials"in the industry, it refers to plastic materials generated in production or recycled in the market for reuse. It is a general term that is generally divided into two categories: factory recycled materials and market recycled materials.
——In plant material recycling (machine head material/water outlet material)
Source: uncontaminated materials such as cut edge materials, machine head materials, and trial materials generated during the production process, which are crushed and reused.
Characteristics: - Same as the production raw material formula, with minimal performance changes; ——Pollution free and traceable; ——The general blending ratio is not higher than 10%.
Scope of application: It can be used to continue producing original grade pipes, provided that the mixing amount is controlled within a reasonable range.
——Market recycled materials (recycled materials)
Source: Raw materials obtained from recycling, cleaning, sorting, and re granulation of waste pipes, packaging plastics, plastic products, and other materials.
Characteristics: The material source is unstable and may be a mixture of different materials (such as PE and PP); ——There is an odor, black spots, and impurities; ——The performance has significantly decreased, the melt index fluctuates greatly, and the hygiene performance is poor.
Scope of application: Only used for products that are not under pressure, non critical, and have low lifespan requirements, such as cable conduits, underground sewage auxiliary pipes, drainage ditch covers, etc.
5、 Mixing ingredients
The term 'mixed ingredients' has a dual meaning in the plastic pipeline industry, which can easily cause misunderstandings and must be specifically explained.
(1) Standard definition of"mixed ingredients"
In national standards such as GB/T 13663-2020 and GB/T 19472.1, blending refers to a pre mixed granular material made from polyethylene resin as the base resin, with the addition of antioxidants, processing aids, color masterbatch and other additives, processed through processes such as melt mixing and extrusion granulation.
This type of mixed material has stable performance and controllable quality, and is usually produced by professional raw material enterprises such as Sinopec, PetroChina, Basel, Boru, etc. Some pipe manufacturers also have self-produced capabilities.
Scope of application: High performance applications such as drinking water pipes and gas pipes.
(2) The term 'mixed ingredients' in industry jargon
However, in actual market communication, what people often refer to as"mixed ingredients"generally refers to raw materials that are directly physically mixed in proportion from different grades of raw materials (such as new materials, secondary materials, recycled materials, and even recycled materials) and used without melting or granulation.
This"blending material"is essentially a formula material that simplifies costs, and its performance is greatly affected by fluctuations in the type, proportion, and batch of raw materials added.
Common applications: electrical conduit, agricultural irrigation pipe, drainage pipe and other products with low performance requirements.
Ultimately, the performance of plastic pipes largely depends on the type of raw materials used. Whether it's new materials, sub brand materials, recycled materials, or mixed materials, each has its own characteristics and applicable scenarios.
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