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 crystallization 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: hot rolled is relative to the cold-rolled, cold rolling is below the recrystallization temperature of the rolling, and hot rolled is carried out at above the recrystallization temperature of the rolling.

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.

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.

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.

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.

Advantages

hot rollded seamless steel pipe can damage the cast microstructure of the steel ingot, refinement of the crystal grains of the steel, and eliminate the defects of the microstructure, so that the the steel organization compacting, improve the mechanical properties. This improvement is reflected in the rolling direction, so that the steel is no longer to a certain extent isotropic; pouring the formation of bubbles, cracks, and osteoporosis, under high temperature and pressure can also be welded together.

Disadvantages:

  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 °.

Hot rolled seamless steel pipe

Hot-rolled seamless steel pipe defects

a. Inner surface defects

An inner flap: presenting a straight line, a spiral or a semi-helical sawtooth defect on the inner surface of the steel pipe.

  • Inside scarring: scars in the steel pipe inner surface, generally easily peel off.
  • Warping: a straight line or intermittent small nail-like tilt leather. Often seen in the capillary head, and easy to peel.
  • Inside straights: a straight shape scratch with a certain width and depth.
  • Iinner edge: a straight shape protrusion with a certain width and depth.
  • inner drum kits: a super and regular protrusion and outer surface is not damaged.
  • Pull pits: a regular or non-regular pit and the outer surface without damage.
  • 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.

b. outer surface defects

An outer fold: the outer surface of the pipe presents a layered folded spiral.

  • separation: presenting a spiral shape or blocky delamination and cracking.
  • external scarring: scars on the outer surface.
  • pock surface: steel surface showed uneven pits.
  • Line: a substantially symmetrical or asymmetrical linear rolling marks.
  • Hairline: a continuous or discontinuous hairy fine lines.
  • net cracks: scaly small cracks.
  • scratches: linear or spiral-shaped groove-like defects.
  • touch deflated: the outer surface of the steel pipe rendered in a convex outer concave phenomenon, and pipe wall thickness without injury.
  • bumps: collision irregular scars.
  • straightening recess: steel spiral concave outer surface.
  • rolled off: longitudinally local or long presentation in a convex outer concave folds, the outer surface into strips depression.
  • crack:opened the rupture surface phenomenon, much produced in the thin-walled tube.

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ASTM

ASTM's steel standards are instrumental in classifying, evaluating, and specifying the material, chemical, mechanical, and metallurgical properties of the different types of steels, which are primarily used in the production of mechanical components, industrial parts, and construction elements, as well as other accessories related to them.

  • ASTM A 53 specification for black steel seamless pipes
  • ASTM A 106 Gr. B seamless carbon steel pipes for high-temperature service
  • ASTM A333 (ASME S/A-333) Pipe grades permit low temperature service.
  • ASTM A335 Pipe is a seamless ferritic Alloy-Steel Pipe for high temperature service.
  • ASTM A 210 specification for seamless medium-carbon steel boiler and superheater pipes
  • ASTM A 519 seamless carbon and alloy steel for mechanical tubing
  • ASTM A 556 seamless cold-drawn carbon steel feedwater heater tubes
DIN

DIN Standards are the results of work at national, European and/or international level.

  • DIN 17175 seamless steel tube for elevated temperature
  • DIN 2391 cold drawn seamless precision pipes

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.


Seamless pipe Specification, standard and identification

Seamless pipes are extensively applied for the nuclear device, gas, petrochemical, ship building and boiler industries. Seamless pipes dominates 65% of market share in Chinese boiler industry.