Especially the gas pipeline explosion accident that occurred in Yanjiao Town, Hebei Province on March 13th this year has sounded an alarm for municipal pipelines. Therefore, ensuring the quality of pipe materials is crucial and urgent for safeguarding consumer rights and interests.
Although pipeline construction units can select suitable suppliers based on factors such as brand reputation and manufacturer scale when choosing plastic pipes, given the vast market of the plastic pipe industry and the phenomenon of numerous manufacturers and uneven product prices and quality, relying solely on the brand name cannot guarantee absolute success.
Therefore, after completing the procurement process, we must strictly follow a rigorous workflow, implement a strict incoming inspection mechanism, and verify the actual quality of the purchased pipes in a scientific and accurate manner, thereby effectively reducing procurement risks, preventing the inflow of unqualified products, and avoiding potential harm or adverse effects on consumers and downstream industrial chains. So the question is, how should you inspect the plastic tube in your hand that looks structurally simple, and what can be inspected to confirm that it meets your requirements? Sampling inspection of pipes is like coming to a hospital for a physical examination. There are more than ten performance indicators of pipes, and the cost of testing is not low. How to choose suitable inspection items, "prescribe the right medicine" and "use good steel on the cutting edge", many procurement personnel are actually confused about how to inspect them with confidence and peace of mind.
Today, I will introduce several testing methods for plastic pipes.
Conventional incoming inspection/sampling/testing?
Plan 01
Appearance, geometric dimensions (average outer diameter, wall thickness and deviation, length), physical and chemical inspection items (to be considered as appropriate).
Tips
As a purchaser of pipes, if conditions permit, one may consider investing in the testing capabilities of self built appearance and geometric dimensions projects. These two projects are relatively simple, do not require high levels of expertise in personnel and equipment, have the lowest implementation cost, and based on the process of plastic pipes, appearance and geometric dimensions are the most frequently unqualified testing items. For example, the compressive strength of pressure pipes, excluding the influence of material properties, wall thickness is one of the most direct parameters affecting it.
Scenario 02
The storage of PE gas/water pipeline system has exceeded its expiration date, with a distance of more than N years from the production date (such as 1.5 years, 4 years)
Plan 02
Pipe material: elongation at break, static hydraulic strength at 80 ℃/165h, peel strength of electric fusion joint;
Pipe fittings: static hydraulic strength at 80 ℃/165h, tensile failure mode of hot melt butt welded joints (only hot melt), peel strength of electric melt joints;
Valve: 80 ℃/165h static hydraulic strength, peel strength of electric fusion joint, operating torque, sealing performance test.
Tips
This is a situation that I often encounter in my current work, which has clear solutions in the construction standards CJJ63 and CJJ101.
Due to various factors such as improper material management in actual engineering, failure to achieve first in, first out may result in material obsolescence. Therefore, re inspection of these items can be conducted to re evaluate whether they can be reused.
Scenario 03
The PE pipeline was broken during construction
Plan 03
Tensile failure mode, tensile yield stress/tensile strength of hot-melt butt joints
Tips
In non excavation pipeline crossing projects, deformation and fracture of pipelines often occur during the dragging process. The reason for this is that the tensile force borne by the pipe exceeds its own strength, causing the pipe to yield and counteract the tensile force through deformation.
Previously, the requirements for the tensile strength of plastic in PE pipes were not very clear. Now, there are clear requirements in construction specifications and product standards. The tensile strength of PE80 grade materials should not be less than 18.0MPa, and the tensile strength of PE100 grade materials should not be less than 21.0MPa.
The construction worker should calculate the maximum tensile force applied to the pipeline according to the maximum force formula in the construction specifications. If the pipeline deforms, fractures or cracks at the joint without exceeding the maximum tensile force, re inspection of these items can be carried out to re evaluate the quality of the pipe material or joint welding quality.
Scenario 04
Regular inspection of in-service PE gas pipes
Plan 04
Static hydraulic strength (80 ℃/165h), elongation at break, resistance to slow crack growth, oxidation induction time, tensile failure mode of hot melt butt welded joints, tensile peeling/extrusion peeling
Tips
At present, polyethylene gas pipes have been used in China for more than 30 years, and some pipe networks have already shown signs of aging. According to relevant laws and regulations, regular inspections of gas transmission pipe networks should be carried out. For high-risk pipe sections, excavation sampling should be carried out to identify their quality condition and determine whether they can continue to be used. If there is a possibility of material degradation, it is necessary to; The ambient temperature for pipeline laying exceeds 40 ℃; Pressure pipeline components without manufacturing supervision and inspection reports; The service life has exceeded 10 years; Pipelines with unclear material conditions or without installation and supervision; Excavation inspection revealed defects such as bulging, bubbles, groove marks, or depressions.
It is worth noting that the inspection results of in-service pipelines are not judged according to GB/T 15558. Currently, each province has its own industry standards or group standards, and the inspection items and limit requirements are also different. However, in-service pipelines have been in use for many years, and their inspection results are likely to no longer meet the judgment standards at the time of leaving the factory. In actual inspections, risk level assessments are conducted based on the inspection results, and high-risk pipeline sections should be considered for timely replacement.
In the author's opinion, the performance changes of in-service pipelines are closely related to the raw materials of the pipes. The situation of mixing materials is much better than that of white and black, and the performance difference between imported materials and domestic materials is not small. In fact, pipes that have been used for 15-16 years have been tested and the test results are also qualified. However, some pipes that have been used for only 5-6 years may be found to be unqualified after testing. There are many cases where the elongation at break test fails, and in addition, the pipeline is affected by environmental oxidation. Oxidation induced sampling from the inner and outer walls, as well as the middle of the pipe, can result in significant differences in numerical values. With further oxidation from the outside to the inside, the pressure bearing performance of the entire pipe will gradually decrease.
Scenario 05
Suspect that the pipeline has used recycled/reclaimed/regenerated materials?
Plan 05
Appearance, trace metal element content (iron, calcium), ash content, hygiene performance (only for water supply pipes)
Tips
As a plastic pipe, its recyclability has always been its advantage over other metal and non-metal pipes. But some manufacturers, in order to reduce costs, produce pipes by mixing cheap recycled materials, reclaimed materials/recycled materials, but at the same time, it greatly reduces the quality and safety of the pipes.
In the past, standards allowed for the addition of small amounts of recycled materials, but the hygiene and purity of the recycling process were difficult to control, and the lower quality of recycled materials caused great concern for end users. Whether recycled materials have been added to the pipes can be determined by the appearance and odor of the producers, but a more accurate judgment can be made by detecting the content of trace metal elements (iron, calcium) and ash content.
In the new national standards GB/T 13663.2 and GB/T 15558.2, both have limited value requirements, and pipes that exceed the limits will not be wrongly accused. In 2014, a focus interview revealed that some manufacturers in Qidu Town, Suzhou City used medical waste plastic to produce drinking water pipes, which made it difficult to meet hygiene standards.
Scenario 06
Suspect that the pipeline did not use a certain brand of material as required
Plan 06
Component identification and analysis
Tips
In the plastic pipe industry, especially in the gas pipe industry, end customers will select a certain brand of materials from designated suppliers according to national standards. Due to differences in market share and reputation, the prices of materials from different brands also vary greatly. Some manufacturers, in order to reduce costs, will use low-priced brand materials as inferior ones and impersonate higher priced brand materials.
In this case, only the pipe section can be selected and sent to the manufacturer of the nominal raw material for component traceability analysis. The raw material manufacturer will determine whether its characteristics meet its internal control requirements based on the formula and elemental composition of the material, and ultimately give a conclusion on whether the pipe was produced entirely using a certain brand of material.
Scenario 07
Welding Procedure Qualification
Plan 07
Hot melt evaluation: macroscopic inspection of appearance (symmetry and alignment of rolled edges), cutting inspection, back bending test, tensile failure mode of hot melt butt welded joints, 80 ℃ static hydraulic strength
Electric melting evaluation: macroscopic appearance inspection, electric melting pipe section inspection, extrusion peeling/tensile peeling/tear peeling, 80 ℃ static hydraulic strength
Tips
In the plastic pipe industry, especially in the gas and heat pipe industries, hot melt and electric melt connections are currently mainly used for construction. There are requirements for welding process qualification in CJJ63 and T/CDHA 501.
Scenario 08
Type inspection, type inspection
Plan 08
Appearance, color, size, hydrostatic strength (20 ℃, 80 ℃), elongation at break, resistance to slow crack growth, resistance to rapid crack propagation, compression recovery, longitudinal shrinkage rate, oxidation induction time, ash content, carbon black content, carbon black dispersion, melt mass flow rate, as well as gas composition resistance, weather resistance, trace metal element content, strain hardening test, etc
Tips
Typing inspection and type inspection are generally required by pipe enterprises. As consumers, if they want to evaluate the quality of their purchased products, they can refer to these items. However, conducting a full inspection once is costly and not advisable.
Generally, pipe companies conduct regular type inspections, control point inspections, etc. For reports from authoritative testing institutions, they can consider directly accepting them. High cost testing items such as rapid crack propagation, 80 ℃ 1000h hydrostatic pressure, weather resistance, gas resistance components, etc. are not suitable for consumer sampling verification.
Can scratched pipes still be used
Plan 09
Size (wall thickness)
Tips
Plastic pipes have a soft texture and are prone to scratches and damage. In CJJ63, it is also stipulated that if the wall thickness is scratched and the loss exceeds 10% or 4mm, the damaged pipe should be cut off and discarded.
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