Pipes and tubular conduits – Reinforced
Reexamination Certificate
2001-02-13
2002-08-20
Brinson, Patrick (Department: 3752)
Pipes and tubular conduits
Reinforced
C138S178000, C138SDIG002
Reexamination Certificate
active
06435218
ABSTRACT:
CROSS-REFERENCES TO RELATED APPLICATIONS
This application claims the priority of German Patent Application Serial No. 100 09 305.1, filed Feb. 22, 2000, the subject matter of which is incorporated herein by reference.
BACKGROUND OF THE INVENTION
The present invention relates, in general, to the protection of a pipe section against propagation of cracks, and more particularly to a steel pipe of a type having an outer corrosion-preventive protective sheath, which includes a plastic surface layer, and a crack stopper zone, which extends over a section of the pipe. The present invention also relates to a process for making such a pipe.
Steel pipes or pipelines are often used for transport of fluid under comparably high pressure. Depending on the application, these pipes or pipelines are endangered by formation of cracks and fissures, when exposed to the stress at hand. Even though, this may be a rare event, the formation of cracks may have catastrophic results, e.g. when transporting gaseous fluids, such as transport of natural gas through pipelines of great diameters. Under certain conditions, such cracks may rapidly propagate over long distances of the pipeline. In order to keep the damage in check, proposals have been made to provide so-called crack stoppers along predetermined distances in the pipeline so as to limit crack propagation between two crack stoppers. Many proposals have been made in order to configure such crack stopper zones.
German Pat. No. DE 31 35 966 C2 describes a method of making multi-layer welded pipes, called helical seam steel pipes. Hereby, the individual layers are welded, separate from one another, to pipes. After nesting the pipes within one another, the pipes are then mechanically expanded to a preset outer diameter and joined together. Welding of the helical welding seam steel pipes is realized by providing a difference in diameter of the pipes that is suitable for nesting purposes. The pipes being utilized have helical welding seams of different helix angle so that the helical seams of the individual pipe layers intersect. The production of multi-layer pipes in this type is very complicated.
German Pat. No. DE 34 37 564 C2 describes a steel pipe for use as crack stopper for gas pipelines. The steel pipe includes several layers, typically two or three layers made of strips or sheet metal. In case of a two-layer configuration, the inner layer is significantly thicker than the outer layer and has on its outer surface a plurality of notches which extend at an angle between 35° and 70° in relation to the pipe axis so that any imaginary geometric axial line on the steel pipe passes at least through one of the notches. In case of a three-layer configuration, the center layer is formed with such notches or even continuous grooves. In any event, the obliquely oriented notches or grooves are neither directly accessible from the pipe inside or from the pipe outside. The entire wall thickness of this multi-layer crack stopper has a same thickness as the pipes of the respective pipeline. The individual layers of the crack stopper are welded together in circumferential direction along their end faces. Any crack in the pipeline, typically cracks running along the geometrical surface line, is ensured to reach one of the notches oriented obliquely to the crack migration so that the crack is deflected in circumferential direction and brought to a standstill.
German Pat. No. DE 32 08 452 A1 describes a crack stopper in the form of a cylindrical sleeve of an inner diameter which is greater than the outer diameter of the respective pipeline in which the sleeve is fitted. The outer peripheral surface of the sleeve includes at least one opening and is pushed along a portion of the pipeline and so centered with respect to the pipe axis that an annular space is formed between the inner surface of the sleeve and the outer surface of the pipeline. The annular space is sealed on its end faces, for example, by an outer strip. Subsequently, a curable filling material is pressed through the opening in the sleeve. Once cured, the filling material has still an elastic consistency. An example for use as filling material is urethane elastomer. The sleeve is typically made of a same material as the actual pipeline. The filling of the annular space with plastic is supposed to prevent a corrosion of the steel pipe in the area of the crack stopper. The fabrication of this type of crack stopper is rather complicated because it not only requires a centering of the sleeve but also a sealing of the openings at the end faces and a proper filling of the spaces with plastic. Furthermore, the thick-walled sleeve substantially increases the outer diameter and the weight.
German Pat. No. 30 32 176 A1 describes another type of crack stopper which includes a tubular body portion having two truncated cone shaped sections, which are sloped inwardly, and an intermediate section of reduced diameter at the outer surface. A cylindrical reinforcing member loosely embraces the cylindrical intermediate section and may be formed as a reinforcing sleeve. The reinforcing member may also be made of a strip or cable wrapped around the cylindrical section. To the outside, the crack stopper is surrounded over its entire length by a smooth cylindrical sheet metal shield, and the remaining space between the truncated cone shaped sections and this shield is filled with a filler material. This type of crack stopper is also very difficult to fabricate. Although the crack stopper does not result in a significant increase of the pipeline diameter, it is disadvantageous that the inner diameter of the cylindrical section of the crack stoppers is considerably smaller than the inner diameter of the remaining pipeline. This results not only in an undesired flow resistance but is also an obstacle when forcing a scraper through the pipeline.
It is also known to integrate by welding in a pipeline short pipes as crack stoppers, having a wall thickness which is thicker (e.g., twice the thickness) than the wall thickness of the remaining pipeline. The effectiveness of such crack stoppers is dependent not only on the calculated reduction of tensile stress in the pipe wall but also significantly on the fact that the thick-walled pipes are tough enough. In particular, when pipelines of high tensile steel such as X90 and X100 are involved, physical limitations are quickly reached that cannot be overcome. As thick-walled pipes normally are produced with a significantly smaller ductility than thin-walled large-sized pipes, thick-walled large-size pipes of such steels have typically a coarser texture and thus significantly poorer toughness than corresponding thin-walled large-size pipes for the actual pipeline. This type of crack stopper is therefore unsuitable for high-strength steels for use in pipelines.
International patent publication WO 94/29633 describes a protective plastic cover for a pipeline. The cover is made of half-shells configured as an outer bandage in the form of a sheet metal strap or plastic strap, or a hook-and-loop fastener strap. The material of the cover may be reinforced by fiber material. The protective cover is intended to prevent damage of the pipeline as a result of external forces, such as through impact of an excavator bucket, and to provide better visibility. The cover may have a mat-like configuration and can be wrapped on a pipeline in several layers and held together, for example, by straps or hook-and-loop fastener straps.
It would be desirable and advantageous to provide a pipe with improved crack stopping feature which obviates prior art shortcomings and which is easy to make and results in an insignificant weight increase, while yet is reliable in operation even for pipelines of high-strength steels.
SUMMARY OF THE INVENTION
According to one aspect, the present invention provides for a steel pipe, including an outer corrosion-preventive protective sheath, which includes a surface layer of plastic material, e.g. thermoplastics, and a crack stopper zone, which extends over a section of the pipe, wher
Arndt Johannes
Hillenbrand Hans-Georg
Junker Gerd
Knauf Gerhard
Von Hagen Ingo
Brinson Patrick
Feiereisen Henry M.
Mannesmann AG
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