Hot-rolled seamless steel pipe

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 °.