Major Defects of Cold Drawn Seamless Stainless Steel Pipe

t Pipe material or bad quality intermediate tube quality, including geometry does not meet the requirements, the longitudinal and transverse serious uneven wall thickness, curvature and through the large oval, chemical composition or not, the mechanical properties of substandard or unequally; u did not comply each step of the preparation procedures before pulling system. The main process is hammer incorrect, improper chemical processing and heat treatment operations, the pipe end burr, grinding quality is not high defects during transport, etc; v not abide by the rules extubation process. The performance of the tube centerline and line drawing made inconsistent extubation die properly installed, launching too fast, improper matching tool mandrel rod diameter is too large or too small, too large amount of deformation, the mandrel feeding untimely ; w extubation die and mandrel of the worst quality, including poor finish, low hardness and strength, dimensional irregularities, carbide die inserts such as incorrect; x extubation disrepair. As the car tilt extubation, extubation die or die holder itself is not properly installed in the center and other shelves.

Regarding the mainly drawn tube defects, in particular their causes and elimination methods:
t. Fold:
Folding present in the steel pipe outer surface or the inner surface, straight or spiral, continuous or discontinuous. Folding the main reason is poor quality pipe material, itself folded, or surface inclusions, severe scratches and cracks, grinding angular in place, by extending the emergence folded pull system. In order to avoid the generation of folding, it should improve the quality and attention to check the pipe material and grinding.

u. Crack:
Cracks (including cracks, hairline) refers to straight or spiral hairline cracks on the inner and outer surfaces of the distribution pipe was a depth of 1 mm or 1 mm or more, there is a continuous and discontinuous. Causes are: Hot- rolled billet subcutaneous subcutaneous bubbles and inclusions, cracks or deep pitting on the front pipe drawing mill, hot-rolled or cold-drawn at each step operation generated a longitudinal channel or scratch scratch. Also prevent the formation of cracks is to improve the quality of pipe material, pipe material to strengthen the inspection of grinding. While avoiding tube pitting in cold drawing production process, designated trails and abrasions.

v. Pit:
That area of pits distributed over the surface of the steel pipe of varying local depression, distribution and some cyclical, some erratic. Pit was the result of iron oxide or other hard dirt in the process of straightening pull system or pressed into the surface of the pipe or the pipe is originally present in the surface of the skin peeling Alice. Measures to prevent the pit is carefully checked tubing and remove warping and other defects, clean workplace, tools and lubricants to prevent oxide scale and dirt fell on the steel surface.

w. Diameter tolerance:
The main reason for the difference in diameter ultra-diameter tolerance is molded with improper or neglected extubation size changes caused due to wear. Straightening process of straightening rollers can also cause excessive pressure pipe diameter is too small.

x. Wall thickness tolerance:
The main reason for the wall thickness of the wall thickness tolerance tolerance is inappropriate with mold, or ignore the changes in die size due to wear caused. After a given amount of change in the wall thickness of the wall of an empty drawing passes in inaccurate estimates, the use of curved conical mandrel and the outer mold when short-mandrel drawing mill mandrel position properly adjusted before or after a transient. In order to prevent the wall thickness tolerance, the mold should be properly equipped, properly adjust the position of the mandrel. Empty Stubbs passes in pipe wall thickness variation should be estimated accurately.

y. Oval:
Oval pipe cross-section that is oval. Used in the drawing process is the die hole is oval-shaped pipe ends extubation die or due to excessive bending, straightening process ran up and down when straightening, pipe diameter is too large pushed stuck pipe tail swinging through the reduction will produce uneven distribution etc. this defect between the large and each pair of straightening rolls. If the die holes and elliptical defects should be replaced extubation die. If the ellipse is formed in the straightening process should result in the elimination on the cause of the ellipse when straightening.

z. Uneven thickness:
Mainly produce steel pipe wall thickness uneven thickness is uneven; tubing uneven wall thickness is too large, pull-line and pipe axis inconsistent pull system, the core pressing and extubation die die orifice oval. In order to reduce the wall thickness of the pipe is uneven, the wall thickness of the tube material should be as small as possible without, at the same time should be carefully checked and adjusted extubation die.

{. Road planning and abrasions:
Road and feature zoned scratch defects that render appropriate longitudinal linear varying lengths of scratches on the inside and outside surfaces of steel, more groove-shaped, but may also be raised stripes. Road planning and scrapes main reason is: the inner tube material have designated channel when the system fails to eliminate the drawing, the steel remnants of iron oxide, bonded steel mold, mold strength and hardness of insufficient or uneven mold appears broken crack and wear, poor hammer, hammer sharp angle transition portion of the shuttle damaged mold. In order to prevent abrasion and scratch track should enhance the quality of each preparation step before pulling system and the use of high strength and hardness, good finish mold.

|. Pull off:
Pull off pull off the main reason for the emergence of: excessive deformation, not heat treated pickled lubrication quality, hammer undesirable, when heated to produce a hammer in front of overheating or over-burning, pulling and pipe- line axis inconsistent, short mandrel protruding sizing extubation die before passing, launching too fast and so on. To prevent pull off, pull the pipe system before the die size and distribution should be strictly carried out in accordance with the provisions of pull tabs, should Anzheng extubation die, mandrel position to be correct, should ensure the quality of each system before drawing the preparation process, in drawing manufactured under high speed, the
speed is reduced when launching. When short - mandrel drawing time and space to pull over the length of the mandrel head pull system, the pipe wall thickness exist for a period not greater than a predetermined length of the wall thickness of the empty drawing mill plucking head is normal. However, if the air is too long plucking head will increase the amount of crop, increased metal consumption. It appears empty plucking head long because when launching the mandrel is pushed into the mandrel is not timely or can not be brought into the pipe deformation zone. When the former situation, should pay attention to the operation and use locator. If the mandrel can not enter the deformation zone, can be polished in the grinding wheel at the ends of the chamfered mandrel, so as to favor into the deformation zone.

}. Shaking pattern:
Shaking pattern produced only during a short mandrel drawing mill. Appears when shaking groove on the inner surface of the pipe or the inner and outer surfaces rendered uneven, wavy ring a different number of marks, some continuous, some
intermittent, may be full circle, it may not complete revolution. So feed grain to produce, due to the drawing process is in the pipe and the mandrel rod happened jitter. Jitters specific countries of origin are: good quality pickling and lubrication, friction increases and changing when drawing mill, heat treatment is inconsistent along the length of the mechanical properties of steel, mandrel rod is too long too small, front position over the mandrel or later, excessive deformation and the like. In order to prevent the shaking of grain production, should improve the quality of pickling, lubrication and heat treatment, the right to adjust the position of the mandrel, avoid using too small diameter mandrel rod.

~. Longitudinal cracking:
This defect occurs when longitudinal cracks, penetrate the wall of the steel pipe exhibits longitudinal split, with a burst of Health. Generally occurs in the full-length, sometimes it occurs in part by the end of the hammer. Longitudinal cracks usually only empty extubation appear because of the outer surface of the steel pipe after pulling a large empty tangential tensile residual stresses. Longitudinal cracking caused by specific reasons are: reducing the amount is too large, increasing the degree of non-uniform deformation, residual stress increases; even pull pull pass too empty, pipe resulting in a larger residual stress and work hardening phenomenon; improper annealing including the
temperature is too low, uneven temperature or time is too short; after the hammer transition portion recessed too deep or partial wall drawing made after the end of pipe missing a notch stress concentration; not timely prepared baking after drawing or annealing and a blow when resting; folding steel surface defects such as hydrogen embrittlement, and the like. Poor cold workability of steel, thick-walled steel pipe and low temperature greater tendency temporal extubation occurs longitudinal cracking. Pipe is a longitudinal cracking irreparable defects occur, on steel scrap. Prevent longitudinal cracking pipe, pull the control room should be reducing the amount of passes and even pull the number, quality assurance and hammer heat treatment to avoid hydrogen embrittlement, the steel pipe after drawing system should be annealed.

. Wall longitudinal recesses:
Wall longitudinal recesses occur in the air and pull the thin-walled special thin-walled tube, the drawing process is due to the cross-section of the pipe caused by the loss of stability. Specific reasons for reducing excessive. If the hammer end wall transition portion local depression too deep will increase the tendency to produce longitudinal recesses. When pulling thin-walled and especially thin-walled tube to prevent longitudinal recesses, reducing the amount of smaller, better quality hammer, it can also be used to pull the dual-mode system.

€. Warping:
Alice skin wherein the inner and outer surfaces of the steel pipe has a partial separation of the metal substrate sheet into a massive individual, discrete, root or not root in the wall, but not the natural exfoliation. Causes are: bad steel, subcutaneous bubbles, exposed Alice belt in hot rolling after cold drawn to produce cold-drawn;

�. Inclusions:
Mixed performance in the steel surface or surface cracks embedded non-metallic inclusions. Causes is bad or when the steel tube or pipe annealing heat pressed into the surface impurities.

‚. Pock:
Pock wherein the steel sheet surface showed a small point-like pits. Ma face the main reason is to produce pitting pickling, annealing after straightening iron oxide skin is too thick pressed into the surface of the steel pipe, steel pipe corrosion save bad happened.

ƒ. Touch (pressure) depression:
Touch (pressure) is mainly produced in the thin-walled tube recess. It causes the handling, especially when lifting improperly released after annealing steel piling too many low-level pipe is pressed recess, when straightening steel swinging, holding tight when the pipe cutting.