Steel pipes for oil casing raw materials

According to the manufacturing method, steel pipes can be divided into two categories: seamless steel pipes and welded seam steel pipes. Among them, ERW steel pipe is the main variety of welded seam steel pipe. Two types of steel pipes used as raw materials for octg casing: seamless vs welded pipes.

Seamless casing - casing made of seamless pipe as raw material
Seamless pipe refers to steel pipes manufactured by four methods: hot rolling, cold rolling, hot drawing, and cold drawing. The pipe itself does not have any welds.

ERW casing - casing made of electric welded pipe as raw material
ERW pipe refers to a straight seam welded pipe manufactured by a high frequency resistance welding process. The raw steel plate (coil) of ERW welded pipe is made of low carbon microalloy steel rolled by TMCP.

Outer diameter tolerance

Seamless steel pipe: hot rolling forming process is adopted, and its sizing is completed at about 8000C. The raw material composition of the steel pipe, cooling conditions and cooling state of the roll have a great influence on its outer diameter, so the outer diameter control is difficult to be accurate and fluctuates. Larger range.

ERW steel pipe: cold-formed, sizing is completed by 0.6% diameter reduction, and the process temperature is basically constant at room temperature, so the outer diameter is controlled accurately and the fluctuation range is small, which is conducive to eliminating black leather buckles;

Wall Thickness Tolerance

Seamless steel pipe: It is produced by round steel perforation, and the wall thickness deviation is relatively large. The subsequent hot rolling can partially eliminate the wall thickness unevenness, but the most advanced unit can only control it within ±5-10%t.

ERW steel pipe: hot-rolled coils are used as raw materials, and the thickness tolerance of modern hot-rolled strips can be controlled within 0.05mm.

Exterior

The defects on the outer surface of the billet used in the seamless steel pipe cannot be eliminated by the hot rolling process, and can only be polished off after the finished product is completed; for the spiral path left after piercing, it can only be partially eliminated during the wall reduction process.

ERW steel pipes use hot-rolled coils as raw materials. The surface quality of coils is the surface quality of ERW steel pipes, and the surface quality of hot-rolled coils is easy to control and of high quality, so the surface quality of ERW steel pipes is much better than seamless steel pipes. .

Ovality

Seamless steel pipe: hot rolling forming process is adopted, the steel pipe raw material composition, cooling conditions and the cooling state of the roll have a great influence on its outer diameter, so the outer diameter control is difficult to be accurate, and the fluctuation range is large.

ERW steel pipe: It is formed by cold bending, so the outer diameter is controlled accurately and the fluctuation range is small.

Stretching test

The tensile properties of seamless steel pipes and ERW steel pipes are in line with API standards, but the strength of seamless steel pipes is generally at the upper limit, and the plasticity is at the lower limit. In comparison, the strength index of ERW steel pipes is in the best state, and the plasticity index is 33.3% higher than the standard The reason is that the raw material of ERW steel pipes - the performance of hot-rolled coils is guaranteed by means of micro-alloying smelting, refining outside the furnace, and controlled cooling and controlled rolling; seamless steel pipes mainly rely on means of increasing carbon content, which is difficult to guarantee strength and plasticity. reasonable match.

Hardness

The raw material of ERW steel pipe - hot-rolled strip coil has extremely high precision of controlled cooling and rolling during the rolling process, which can ensure the uniform performance of each part of the strip coil.

Grain size

The raw material of ERW steel pipe - hot-rolled coils are wide and thick continuous casting slabs, which have a thick fine-grained surface solidification layer, no columnar grain area, shrinkage cavity and porosity, small composition deviation, and compact structure; in the subsequent rolling process Among them, the application of controlled cooling and rolling technology further ensures the grain size of raw materials.

Anti-collapse test

ERW steel pipe is characterized by its raw materials and pipe making process. Its wall thickness uniformity and ovality are far superior to seamless steel pipes, which is the main reason why its anti-collapse performance is higher than that of seamless steel pipes.

Impact test

Since the impact toughness of the ERW steel pipe base material is several times that of the seamless steel pipe, the impact toughness at the weld is the key to the ERW steel pipe. Process parameters such as heating power and frequency, welding extrusion amount, intermediate frequency withdrawal temperature and depth, and length of air-cooling section ensure that the impact energy of the weld reaches more than 60% of the base metal. If further optimized, the impact energy of the weld can be close to that of the base metal. materials for seamless performance.

Burst test

The blasting test performance of ERW steel pipes is much higher than the standard requirements, mainly due to the high uniformity of wall thickness and uniform outer diameter of ERW steel pipes.

Straightness

The seamless steel pipe is formed in a plastic state, and it is relatively difficult to control the straightness of the pipe end with a single length (3 to 4 times for continuous rolling);

ERW steel pipe belongs to cold processing, and it has online straightening in the state of reducing diameter, and it is infinitely magnified, so the straightness is better.

10,000-meter footage casing steel consumption

The wall thickness of ERW steel pipe is uniform, and its wall thickness tolerance can be ignored, while the control accuracy limit of seamless steel pipe wall thickness difference is ±5%t, generally controlled at ±5-10%t. In order to ensure that the minimum wall thickness can meet the standard requirements and performance, the only solution is to increase the wall thickness appropriately. Therefore, for casings of the same specification and weight, ERW steel pipes are 5-10% longer than seamless steel pipes, or even more, which reduces the steel consumption of 10,000-meter-foot casings by 5-10%. Even at the same price, ERW bushings virtually save users 5-10% of purchase costs.