What is a hot rolled seamless steel pipe?

What is a hot rolled seamless steel pipe?

Hot-rolled seamless steel pipe is a large category of seamless steel pipe, which is divided according to the production method. Hot rolling is relative to cold rolling, cold rolling is carried out rolling at room temperature, and hot rolling is carried out rolling at the recrystallization temperature. Seamless steel pipe is named relative to the welded steel pipe, seamless steel pipe is usually made of round steel perforation and reprocessing, welded steel pipe is usually welded by steel plate in different ways. The diameter of hot-rolled seamless steel pipe is usually above 38mm. Seamless steel pipe with smaller diameter can be obtained by cold rolling or cold drawing.
Hot-rolled seamless steel pipe is manufactured by hot rolling technology, as the name suggests, the temperature of rolled piece is high, so the deformation resistance is small to achieve large deformation. Take rolling of steel plate for example, the general thickness of continuous casting slab is about 230mm, and after roughing mill and finishing mill, the final thickness is 1~20mm. At the same time, due to the small thickness ratio of steel plate, the dimension accuracy is relatively low, it’s not easy to cause shape problem.

The process of hot-rolled seamless steel pipe:

Hot-rolled seamless steel pipe production base deformation process can be summarized as three stages: perforation, extension and finishing.

Generally process of hot-rolled seamless steel pipe: round bars → heating → piercing → three-roll cross rolling, rolling or extrusion → detached → sizing (or reducing) → cooling → parison tube → straightening → hydrostatic test (or flaw detection) → mark → storage.

Billet is fed into the heating furnace, the temperature is about 1200 degrees Celsius. Fuel for a hydrogen or acetylene. The furnace temperature control is critical to wear air tube round, after the release of pressure puncher. which are generally more common puncher tapered roller punch this punch, high production efficiency, product quality, perforated expanding volume, wearing a variety of steels. After perforation, round tube has been three-roll cross rolling, rolling or extrusion.

After extrusion off pipe sizing. Sizing mill by the high-speed rotation of the cone drill into the Billet punch to form a steel pipe. The steel pipe inner diameter is determined by the length of the outer diameter of the sizing mill drill. After sizing, the steel pipe to enter the cooling tower by the water spray cooling, the steel pipe after cooling, it is necessary to be straightening. Sent by conveyor pipe by straightening the metal detection machine (or hydrostatic test) to conduct an internal flaw. Steel pipe internal issues such as cracks, bubbles will be detected.

Steel pipe quality inspection but also through a rigorous manual selection. Steel pipe of Quality Supervision, Inspection, use spray paint on the number, size, production batch. By a cable car hanging into the warehouse.

Requirements on pipe billet for hot-rolled seamless tube:

Requirements on pipe billet for hot-rolled seamless tube is related to and pipe varieties, uses and piercing methods. For general-purpose steel pipe tube quality requirements can be relaxed more, but the quality of important applications of tube steel and high-alloy steel pipe requirements must be strictly. Stress conditions better or lesser amount of deformation perforation method, without affecting pipe performance conditions, the tube surface and internal quality requirements may be slightly lower. Stress disadvantaged two-roll rotary piercing, if a large amount of deformation perforation, then the tube surface and internal quality have strict requirements. In short, steel tube technical condition is to ensure the quality and smooth production process as the basis to determine, and with different methods vary perforation, with the technical conditions of steel to improve and increase. Technical conditions can be found on a variety of tube standards and technical protocols.

Such as general automatic rolling machine for tube requirements are as follows:

(1) Deviation in Table 1 tube diameter Dp. Tube bending of any part of the ≤6mm / m, tube end face of the cut slope ≤6 ~ 8mm, flattened tube end face of ≤8% Dp;

(2) Tube surface without cracks, hairline, scarring, scaly layer, folding, non-metallic inclusions and residual shrinkage. Not allowed height or depth of more than 0.5mm small grooves, pitting, ears and height of more than two-sided ears of 1mm. Cleanup tube defects deeper than 0.05Dp;

(3) Low magnification tube: not allowed ≥1 level of residual shrinkage, bubbles, anti-leather, white spots and cracks. For the average carbon structural steel billet, which generally loose ≤3 level, center porosity ≤3 level, segregation ≤3 level, subcutaneous bubbles ≤2.

Advantage of hot-rolled seamless steel pipe:
It can destroy the microstructure of ingot casting, grain refinement of steel and eliminate microstructure defects, so that make steel structure compact and improve the mechanical properties. This improvement is mainly reflected in the rolling direction, so that the steel no longer is isotropic; Formation of bubbles, cracks and loose when pouring can also be welded under high temperature and pressure.

Disadvantages of hot-rolled seamless steel pipe:
1 After the hot rolling, the nonmetallic inclusions in the interior of a steel (mainly sulfides and oxides, as well as the silicate) was pressed into a sheet, stratified (laminated) phenomenon appears. The layering of the steel in the thickness direction by the pull performance deteriorated significantly, and may appear in the weld shrinkage interlayer tear. Weld shrinkage induced local strain often reach several times the yield point strain, the strain is much greater than the load caused;
2 Residual stress caused by uneven cooling. The residual stress is the stress of internal self-phase equilibrium in the absence of external force, the hot-rolled steel of various cross-sectional has a residual stress such Usually steel sectional dimension is the greater, the greater the residual stresses. Residual stress is self-phase equilibrium, but the steel members in the performance external force or have a certain influence. Such as deformation, stability, anti-fatigue may adversely.
3 Hot-rolled steel products, poor control of thickness and edge width. We are familiar with the thermal expansion and contraction, even if the beginning of the hot-rolled out are standard length, thickness, or there will be some negative final after cooling, this negative differential edge width wider the increasing thickness of the performance of the more obvious.
So for large steel for steel edge width, thickness, length, angle, and sideline no law requires too precise.

Defect of Hot-rolled Seamless Steel Pipe:
Separation
Located on the inner surface of the steel pipe was vertical distribution, was raised helical, massive metal separation or break-like dissection.
Straight inner flap
Located on the inner surface of the steel pipe was vertical distribution, showing a symmetrical or a single line-shaped folded with through long, there are local.
Irregular hole
Located in the surface of the pipe was vertical distribution, ① has one or two walls 180 °out of thickening, or in the surface of the pipe and the wall thickness of the mandrel separation point has thickened shape, also known as the inner drum kit. ② steel inner garden was a hexagonal shaped uneven thickness, also called hexagon.
Wall contraction
Located on the inner surface of the steel pipe, steel transverse section thinnest steel pipe inner surface depressions, localized thinning of the wall thickness of the severe contraction almost tear.
Rolled scar
Longitudinal direction of the inner surface of steel nails like scarring, bumps or lumps folded inner pipe surface indentation.
Inside folding
Located at the inner surface of the end portion of the steel pipe, local or flaky longitudinal spiral or semi-spiral folding irregular distribution.
Rolling off
Located within the longitudinal surface of the pipe wall was a partial or full length in the outer concave or convex corrugations on the outer surface of the pipe through the long longitudinal grooves prescribe obvious symmetry, generally rectilinear, individual to slash shape.
Tear
Located on the tube longitudinal steel surface showed varying degrees of transverse rupture, diamond-shaped and oval-shaped hole through the tubular body.
Fold the double-slit
Located on the longitudinal surface of the pipe wall obliquely extending into a pair of longitudinal cracks, the cracks sometimes scattered distribution on the pipe circumference sometimes appear symmetrical.
Double centerfold
Located on the longitudinal surface of the pipe wall obliquely extending into a pair of longitudinal cracks, the cracks sometimes scattered distribution on the pipe circumference sometimes appear symmetrical.
Outer folding
① on the outer pipe presents regular folding triangle shaped, double-slit straight single slit straight or irregular sheet folded like.
② Presenting a generally continuous or intermittent stitch sewing machine-like or staggered 60 °, 120 °, 180 ° sewing stitch-shaped folded pipe in the longitudinal direction of the outer。
③ outer longitudinal folded on a spiral steel pipe. 
④ a longitudinal direction of the pipe surface through long or short slash dot folded severe staggered two or three of 120 °.

Outer surface defects of hot-rolled seamless steel pipe:
1. An outer fold: the outer surface of the pipe presents a layered folded spiral.
2. separation: presenting a spiral shape or blocky delamination and cracking.
3. external scarring: scars on the outer surface.
4. pock surface: steel surface showed uneven pits.
5. Line: a substantially symmetrical or asymmetrical linear rolling marks.
6. Hairline: a continuous or discontinuous hairy fine lines.
7. net cracks: scaly small cracks.
8. scratches: linear or spiral-shaped groove-like defects.
9. touch deflated: the outer surface of the steel pipe rendered in a convex outer concave phenomenon, and pipe wall thickness without injury.
10. bumps: collision irregular scars.
11. straightening recess: steel spiral concave outer surface.
12. rolled off: longitudinally local or long presentation in a convex outer concave folds, the outer surface into strips depression.
13. crack:opened the rupture surface phenomenon, much produced in the thin-walled tube.

Inner Surface Defects of Hot-Rolled Seamless Steel Pipe:
1.An inner flap: presenting a straight line, a spiral or a semi-helical sawtooth defect on the inner surface of the steel pipe.
2. Inside scarring: scars in the steel pipe inner surface, generally easily peel off.
3. Warping: a straight line or intermittent small nail-like tilt leather. Often seen in the capillary head, and easy to peel.
4. Inside straights: a straight shape scratch with a certain width and depth.
5. Inner edge: a straight shape protrusion with a certain width and depth.
6. Inner drum kits: a super and regular protrusion and outer surface is not damaged.
7. Pull pits: a regular or non-regular pit and the outer surface without damage.
8. Internal thread (this defect produced only at Accel units): spiral traces often seen in the thin-walled tube surface, and there are obvious rugged feelings.

The application of hot-rolled seamless steel pipe:
1. Construction: it is mainly used to bottom pipeline transportation, that is used to extract groundwater when building houses, and transport hot water for boiler, etc.
2. Machinery: it is used to mechanical processing, bearing sets, processing machinery parts, and so on.
3. Electrical categories: The fluid flowing pipe for gas transmission and water power generation.
4. Other: Anti-static tube for wind power plant.
Yaang is a leading manufacturer of seamless steel pipe, we have the most advanced production line, if you have any requirement of seamless steel pipe, you can send email to us, we will give the best solution.
Source: China Seamless Steel Pipes Manufacturer – Yaang Pipe Industry Co., Limited (www.pipelinedubai.com)

(Yaang Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Super Duplex Stainless Steel Flanges, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. Yaang products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.)

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References:

• https://www.yaang.com