Improvement of hardness and mechanical properties for seamless steel pipe
Date:2019-09-07View:878Tags:Improvement of hardness and mechanical properties for seamless steel pipe
Longitudinal submerged arc welded pipe (LSAW pipe for short). Longitudinal Submerged Arc Welding (LSAW) is a process of pressing (rolling) steel plate into the billet of die or forming machine, using single plate as raw material. Double-sided submerged arc welding is used to enlarge the diameter. The finished product has complete specifications, good weld toughness, good plasticity, uniformity, compactness, large diameter, thick wall, high pressure, low temperature and corrosion resistance.
In the construction of long distance oil and gas pipelines with high strength, high toughness and high quality, most of the required steel pipes are large diameter thick wall straight submerged arc welded pipes. According to API standard, in large oil and gas pipelines, LSAW pipe is the only designated pipeline type in the first and second class areas such as high altitude areas, seabed and densely populated urban areas. According to different forming methods, it can be divided into:
UOE welded pipe: single steel plate pre-bending, U-shaped forming, O-shaped forming, internal welding, external welding, mechanical cold expansion and other processes;
JCOE welded pipe: according to the "J-C-O-E" process, pre-welding, forming, cold expansion after welding;
HME welded pipe: The process of cold expansion after welding is formed by "C-C-O" by spindle rolling.
The main technical parameters of LSAW are as follows:
Wall thickness: X80 grade 6.4-23.8 mm (0.252-0.94 in), X70 grade 6.4-26.4 mm (0.252-1.04 in). As the material decreases, the wall thickness can increase in varying degrees.
Product Standards: ISO3183-3, API Spec 5L, GB9711, etc.
The diameter of LSAW pipe can reach 406.4-1422.4mm.
The length of the steel tube can reach 12.2m, and the wall thickness is 6.4-26.4mm, *70 steel grade.
The main characteristics of LSAW tube are as follows:
1) Longitudinal weld is used for steel pipe and submerged arc welding is used for internal and external welds.
2) After the whole mechanical expansion treatment, the stress inside the steel tube is small and uniformly distributed, which can effectively prevent stress corrosion cracking and has high dimensional accuracy, and is convenient for field welding construction.
3) Using pre-and post-weld technology, the welding process is stable and the quality of the weld is high.
4) Welding is easy to carry out nondestructive testing in the production process, and nondestructive testing can be carried out in the field in the use process.
5) The product specifications range is large, can produce small diameter, large wall thickness, also can produce large diameter, large wall thickness steel pipe.
Improvement of hardness and mechanical properties for seamless steel pipe
Date:2019-11-09View:856Tags:Improvement of hardness and mechanical properties for seamless steel pipe
Longitudinal submerged arc welded pipe (LSAW pipe for short). Longitudinal Submerged Arc Welding (LSAW) is a process of pressing (rolling) steel plate into the billet of die or forming machine, using single plate as raw material. Double-sided submerged arc welding is used to enlarge the diameter. The finished product has complete specifications, good weld toughness, good plasticity, uniformity, compactness, large diameter, thick wall, high pressure, low temperature and corrosion resistance.
In the construction of long distance oil and gas pipelines with high strength, high toughness and high quality, most of the required steel pipes are large diameter thick wall straight submerged arc welded pipes. According to API standard, in large oil and gas pipelines, LSAW pipe is the only designated pipeline type in the first and second class areas such as high altitude areas, seabed and densely populated urban areas. According to different forming methods, it can be divided into:
UOE welded pipe: single steel plate pre-bending, U-shaped forming, O-shaped forming, internal welding, external welding, mechanical cold expansion and other processes;
JCOE welded pipe: according to the "J-C-O-E" process, pre-welding, forming, cold expansion after welding;
HME welded pipe: The process of cold expansion after welding is formed by "C-C-O" by spindle rolling.
The main technical parameters of LSAW are as follows:
Wall thickness: X80 grade 6.4-23.8 mm (0.252-0.94 in), X70 grade 6.4-26.4 mm (0.252-1.04 in). As the material decreases, the wall thickness can increase in varying degrees.
Product Standards: ISO3183-3, API Spec 5L, GB9711, etc.
The diameter of LSAW pipe can reach 406.4-1422.4mm.
The length of the steel tube can reach 12.2m, and the wall thickness is 6.4-26.4mm, *70 steel grade.
The main characteristics of LSAW tube are as follows:
1) Longitudinal weld is used for steel pipe and submerged arc welding is used for internal and external welds.
2) After the whole mechanical expansion treatment, the stress inside the steel tube is small and uniformly distributed, which can effectively prevent stress corrosion cracking and has high dimensional accuracy, and is convenient for field welding construction.
3) Using pre-and post-weld technology, the welding process is stable and the quality of the weld is high.
4) Welding is easy to carry out nondestructive testing in the production process, and nondestructive testing can be carried out in the field in the use process.
5) The product specifications range is large, can produce small diameter, large wall thickness, also can produce large diameter, large wall thickness steel pipe.
Improvement of hardness and mechanical properties for seamless steel pipe
Date:2019-11-11View:856Tags:Improvement of hardness and mechanical properties for seamless steel pipe
Seamless steel pipes are widely used in machinery because of their excellent mechanical properties. However, because it is medium carbon steel, the quenching machine is not good and can harden to HRC 42-46. If the surface hardness is required and the high quality mechanical function of seamless steel pipe is desired, the method is to carburize and quench the surface of seamless steel pipe, so that the required surface hardness can be obtained.
1. After quenching, the hardness of seamless steel tube is higher than HRC55 (up to HRC62) before tempering. The highest hardness in practical application is HRC55 (high frequency quenching HRC58).
2. Seamless steel pipe should not be carburized and quenched by heat treatment process.
After quenching and tempering treatment, the parts have good comprehensive mechanical properties and are widely used in various important structural parts, especially connecting rods, bolts, gears and shafts working under alternating loads. However, the surface hardness is low and wear-resistant. Surface hardness of parts can be improved by quenching and tempering plus surface hardening.
Carburizing treatment is generally used for heavy-duty parts with surface wear resistance and core impact resistance. Its wear resistance is higher than quenching tempering + surface quenching. The surface carbon content is 0.8-1.2%, and the core is usually 0.1-0.25% (in special cases, 0.35%). After heat treatment, high hardness (HRC58-62), low core hardness and impact resistance can be obtained on the surface.
If the seamless steel tube is carburized, the core will produce hard and brittle martensite after quenching, which will lose the strength of carburizing treatment. At present, the carbon content of materials used in carburizing process is not high, the core strength of 0.30% has reached a high level, and has never appeared in practical application. Quenching and tempering plus high frequency surface quenching can be used, but the wear resistance is slightly worse than that of carburizing.
