Urban Gas Pipeline Network Using ERW Pipe and its Anti-corrosion Problems

Comparison of pipe materials used in urban gas pipeline network:
At present, the urban gas pipeline network mainly uses ERW pipes, cast iron pipes and polyethylene (PE) pipes. From the perspective of safety and economy, that is, to ensure the quality of the project, the safety of gas supply and the adaptability of the gas pipe to the gas medium, and to reduce the project In terms of cost, ERW steel pipe is the first choice. Of course, according to local conditions, specific analysis and comprehensive judgment.
1. About cast iron pipes
The advantages of cast iron pipes are corrosion resistance, but there are many disadvantages. The one-time installation is more convenient, but there are many hidden dangers, and it is very troublesome to maintain in the future, the interface is leaking; the pressure bearing capacity is low; the joint strength and impact resistance are low, and the sex is broken; the metal consumption is much, and the unit price is higher.

2. About polyethylene (PE) pipe
(1) When the general gas pipeline network is used, when the residential area is about 11,000 households, the caliber of the medium-pressure main pipe of the gas pipeline network is generally about φ300.
(2) The "PE" pipe has a limit on the maximum operating pressure of the gas, generally 0.1-0.4Mpa; while the ERW steel pipe allows the delivery of gas pressure to a minimum of 7.2Mpa (φ323.9*7.9 L245).
(3) Although the elongation rate of "PE" pipe is higher than that of steel pipe, the tensile strength is only 1/5 of that of steel pipe. It bears pressure and bears the shear force, bending force and tensile force generated on PE pipe due to foundation settlement. Far worse than steel pipes.
(4) In addition, the allowable working pressure of the "PE" pipe at different temperatures is too restrictive and will increase the cost of use. As for SDR11
When -20°CThe requirements of the Technical Specification for Ethylene Gas Pipeline Engineering will differ by 0.3Mpa, making it difficult for on-site engineering and technical personnel to master this scale. Due to the limitation of the ambient temperature, the construction becomes more difficult.

3. ERW steel pipe is the first choice for urban gas pipeline network. The main advantages and disadvantages are:
(1) High strength (large carrying capacity);
(2) The wall thickness is uniform and lighter than cast iron pipes of the same caliber; due to the high delivery pressure, it can be one grade smaller than the caliber of cast iron pipes of the same flow rate. Therefore, the total weight is reduced, the metal is saved, and the cost is reduced;
(3) The price is cheaper than the ductile iron pipe; when the diameter is above 160, the price is cheaper than the "PE" pipe;
(4) The tensile strength is not only greater than the ductile iron pipe, but also 4 times that of the "PE" pipe;
(5) Good plasticity, earthquake resistance and stress crack resistance;
(6) The inner wall of the ERW straight seam welded pipe is smooth, and the friction resistance is small, which avoids the precipitation of gas impurities and the pipeline transportation capacity is improved;
(7) It is suitable for wide temperature range, convenient construction, and tight welding interface. It can adapt to convey gas, liquefied petroleum gas mixed air and natural gas.
(8) However, in general, steel pipes have poor corrosion resistance, and anti-corrosion measures should be taken.

The "Urban Gas Design Code" provides:
Steel pipes are used for gas pipelines with a pressure greater than 0.4Mpa. For medium-pressure and low-pressure gas pipelines with a pressure less than 0.4Mpa, polyethylene pipes, ductile iron pipes with mechanical interfaces, steel pipes or steel skeleton plastic pipes should be used.

It is suitable for urban transportation pipelines. Pipes with a pressure greater than 0.4Mpa are made of steel pipes and have an undisputed position compared with pipes of other materials. Therefore, ERW steel pipe is the first choice for the construction of urban gas pipeline network.

1. Comparing the safety of the main pipes of the city gas pipeline network, the pressure-bearing capacity, tensile strength and elongation of ERW steel pipes are far greater than those of cast-iron pipes. PE" pipe; from the perspective of the tightness of the interface, the welding interface of the ERW steel pipe is much tighter and stronger than the cast iron pipe interface.

2. From the aspect of adaptability, ERW steel pipe is suitable for gas, LNG, LPG, liquefied mixed air and natural gas, while the ability of cast iron pipe to adapt to LNG and natural gas is much worse; the ability of ERW steel pipe to adapt to temperature difference and pressure range It is much larger than the "PE" tube.
3. In terms of economy, ERW steel pipe is cheaper than the ductile iron pipe in unit price and total price. When it is greater than φ 160, ERW steel pipe is also cheaper than "PE" pipe (in general, most urban gas main pipes are in φ300 or so).

4. The corrosion resistance of ERW steel pipe is not as good as that of cast iron pipe and "PE" pipe. This is an important issue to take good anti-corrosion measures during design and construction.