Research on the Performance of Steel Pipes in Low-temperature and High-temperature Environments

Steel pipes play a crucial role in various industrial applications,especially in fields such as petroleum,natural gas,chemical industry,electric power,and ocean engineering.Whether in the extremely cold Arctic or in high-temperature steel mills and thermal power plants,steel pipes need to have excellent temperature resistance to ensure long-term stable operation.This article will deeply explore the performance changes,material selection,and improvement methods of steel pipes in low-temperature and high-temperature environments,so as to help industry users better select and apply steel pipes.

II.Performance Changes of Steel Pipes in Low-temperature Environments

1.Low-temperature Brittleness Effect

When the steel pipe is in a low-temperature environment below zero degrees Celsius,the dislocation movement inside the material is inhibited,resulting in a decrease in plasticity,an increase in brittleness,and even possible fracture.This phenomenon is called"low-temperature brittleness".Generally,the ductility and impact toughness of steel decrease significantly under low-temperature conditions,and in extreme cases,it may even lead to the fracture of the steel pipe.For example,in polar oil and gas pipelines,low-temperature brittleness is an important issue that must be overcome.

2.Low-temperature Impact Toughness

An important index for measuring the performance of steel pipes in low-temperature environments is the Charpy impact test.The impact resistance of the steel pipe is evaluated by measuring the absorbed energy of the steel pipe in a low-temperature state.For example,some special steel grades,such as low-temperature alloy steels(such as 9Ni steel),can still maintain high toughness at low temperatures,thus avoiding brittle fracture.

3.Material Selection in Low-temperature Environments

In order to improve the reliability of steel pipes in low-temperature environments,the following materials are usually used:

Low alloy steels(such as 09MnNiD,A333 Gr.6):They have good low-temperature toughness and are often used in LNG storage tanks and low-temperature pipelines.

Austenitic stainless steels(such as 304,316L):Due to their face-centered cubic(FCC)structure,they still have excellent ductility and toughness at low temperatures.

Nickel-based alloys(such as Inconel 625):They are suitable for extremely low-temperature environments,such as deep sea and liquefied natural gas(LNG)transportation.

III.Performance Changes of Steel Pipes in High-temperature Environments

1.High-temperature Creep and Softening

In a high-temperature environment(>500°C),the steel pipe will experience the phenomenon of creep,that is,slow deformation occurs under long-term stress.In addition,the strength of some carbon steels will decrease significantly at high temperatures,leading to the failure of the steel pipe structure.For example,in power plant boilers,petrochemical plants,and ultra-supercritical steam pipelines,high-temperature creep is a key issue.

2.Oxidation and High-temperature Corrosion

The high-temperature environment will accelerate the oxidation reaction on the surface of the steel pipe,generating a layer of scale(such as Fe₂O₃,Fe₃O₄,etc.).If exposed to a high-temperature oxidation environment for a long time,the oxide layer may fall off,resulting in a decrease in the material thickness and ultimately affecting the service life of the steel pipe.For example,in high-temperature combustion furnaces,heating furnaces and other equipment,the problem of high-temperature corrosion is particularly prominent.

3.Material Selection in High-temperature Environments

In order to deal with various challenges in high-temperature environments,the following materials are usually selected:

Heat-resistant stainless steels(such as 310S,347H):They have excellent high-temperature oxidation resistance and are suitable for high-temperature environments above 800°C.

Cr-Mo alloy steels(such as A335 P91,P92):They are used for high-temperature and high-pressure steam pipelines and have strong creep and oxidation resistance.

Nickel-based alloys(such as Inconel 800H,Hastelloy):They have high-temperature oxidation resistance and are widely used in the petrochemical industry and heat exchanger pipelines.

IV.How to Improve the Temperature Resistance of Steel Pipes?

1.Material Optimization

Adding alloy elements:Such as Ni,Mo,Cr,etc.,to improve the high-temperature or low-temperature resistance of steel pipes.

Using duplex stainless steels:They have both good strength and corrosion resistance and are suitable for harsh environments.

2.Advanced Manufacturing Processes

Controlled rolling and cooling technology:Optimize the structure of steel to improve low-temperature toughness.

Heat treatment(such as quenching+tempering):Improve the high-temperature strength of steel pipes.

3.Surface Protection

Heat-resistant coatings:Such as Al₂O₃,Cr₂O₃coatings,to improve oxidation resistance.

Anti-corrosion coatings:Such as galvanizing,epoxy coatings,to reduce the impact of corrosion.

V.Conclusion

Low-temperature and high-temperature environments pose strict requirements on the performance of steel pipes.The low-temperature environment is likely to lead to brittle fracture,while the high-temperature environment may cause creep,oxidation,and corrosion.Therefore,in different application scenarios,the selection of materials and manufacturing processes for steel pipes is crucial.Through reasonable material selection,advanced manufacturing technologies,and surface protection measures,the service life and reliability of steel pipes in extreme temperature environments can be effectively improved,thus meeting the needs of modern industry.

Whether it is low-temperature deep sea drilling or high-temperature supercritical steam transportation,the reasonable selection of steel pipe materials and protection measures can ensure the safety and long-term use of equipment,providing stable support for engineering projects.