There is a known process applied for the reconditioning of old, worn out steel pipes ? es (-12783/t996), consisting of-the sectioning of the worn out pipe into segments of a certain lengthand attaching a thread to each of their ends in order to join the steel tubes into a pipe. After having threaded and cleaned it on the inside, the steel tube is rotated while its interior is covered with a synthetic resin layer, then a plastic tube is introduced and while pouring additional synthetic resin, first mixed with sand, sawdust or concrete. One end of the plastic tube thus introduced has the pipe's nominal diameter and at the other end there is a plug with a smaller diameter so that it fits hermetically the plastic tube's nominal diameter end secured in the second steel tube The known process has the following disadvantages : - it requires a difficult and expensive threading operation; - it does not ensure an efficient fixing of the plastic tube into the steeLpipeo dich. results Thegative technical effects, - FEw resins, a difficult to handle, toxic and extremely expensive chemical product are needed for the relative attachment of the plastic tube into the steel pipe - great tolerances as to the geometrical shape and the sizes stipulated by the technical standards in force represent a major obstacle to the hermetic hydraulic fixing of the tubes.

The process for pipe internal anticorrosive and anti-erosive protection, according to the invention, consists of introducing a plastic tube into an either new or old steel tube, after having first attached certain items, fixing buttons, by welding or sticking them onto the exterior surface of the plastic tube. These fixing buttons are made of the same material as the plastic tube and once introduced into the steel tube, the plastic tube hardens there by injecting under pressure a mineral binder through a side hole of the steel tube. Prior to this operation, the annular space between the plastic tube exterior surface and the steel tube internal surface had been totaly obstrueted with a sealing system at one end and partially obstructed at the other end in order to allow the air to be evacuated during the mineral binder injection. Once the hinder injected and hardened, the injection hole is welded shut and the plastic tube ends are adjusted and processed in order to allow certain sealing items to be mounted at plastic tube level.

Pipe orientation changes can be achieved-by using steel curves protected on the inside, made both of modulated segments of curve that have internal anticorrosive and anti-erosive protection by means of squirted plastics and of linear pipe sections.

Tightened joining between two straight pipe sections can be achieved by welding at steel tube level and by using a self-healing set at plastic tube level, in the case of non- uniform-internal diameter pipes or a mounting nipple in the case of uniform internal diameter pipes.

Tightened joining between two modulated curve segments or one modulated curve segment and one straight pipe section can be-achieved by welding at pipe steel tube level and by using a self-sealing set at plastic tube level, in the case of non-uniform internal diameter pipes or by welding or sticking plastics in the case of uniform internal diameter pipes-.

The process of internal anticorrosive and anti-erosive protection of steel pipes by means-of squirted-plastics, according to the invention, eliminates the disadvantages listed above, because : - it also allows the steel tubes to be welded together when making pipes protected on the inside by squirted plastics ; - replaces toxic, difficult to handle and expensive-synthetic resins with a non- toxic, easy to handle and very economic mineral-binder ; -it ensures a-perfect fixing of the squirted plastic tube within the steel tube because the plastic. tubes are equipped with fixing buttons and the mineral binder is injected under-pressure into the annular space between the steel and the plastic tubes, - it replaces the sealing plugs of the plastic tubes that are ineffective, difficult to make for the required-geometrical shapes and sizes, with self-sealing sets or mounting nipples; - it allows the creation of curves, forked tubes and other geometrical shapes made out of modulated segments or items; -the process can be applied when making very flexible pipes, either threaded or non-threaded, by using both new steel tubes and old, worn out steel tubes no longer in use; - the pipes obtained by applying this process have a longer operation life than the steel pipe operation life.

Here follows an example of the way the process for steel pipes-anticorrosive and anti- erosive protection by means of squirted plastics can be applied, according to the invention, and also related to pictures 1 = 9, representing: - Picture 1 : General layout of the assemblage for the plastic tube fixing into the steet tube ; -Picture 2: Steel-tube protected on the inside by squirted plastics, used to make non-uniform internal diameter pipes; -Picture 3-: Steel tube protected on the inside by squirted plastics, used to make uniform internal diameter pipes; - Picture 4: Modulated 15° segment, used to create curves of various sizes, protected on the inside by squirted plastics and used for non-uniform internal diameter pipes; - Picture 5: Modulated 15° segment, used to create curves of various sizes, protected on the inside by squirted plastics and used for uniform internal diameter pipes; -Picture-6 : Self-sealing set, used to make non-uniform internal diameter pipes and curves ; - Picture 7: Mounting nipple, used to make uniform internal diameter pipes; - Picture 8 : General layout of a pipe with a curve protected on the inside by squirted plastics and with a non-uniform internal diameter; - Picture 9: General layout of a pipe with a curve protected on the inside by squirted plastics and with a uniform internal diameter.

The process for the steel pipes internal anticorrosive and anti-erosive protection by means of squirted plastics, according to the invention, consists of the attachment of fixing buttons, 1, by welding or sticking them onto the exterior surface of a plastic tube, 2, that is introduced into a steel tube, 3, with a lateral opening, 4, at one of the ends of the steel tube, 3, through which a mineral binder, 5, is injected after having totally obstructed the annular space between the plastic tube, 2, and the steel tube, 3, with a sealing system, 6, at the one end, and a sealing system, 7, at the other end, is designed to allow the air to be evacuated through the upper side during the injection of the binder (picture 1).

After the injection of the binder is finished and the binder hardens, the injection hole is welded-shut, and the plastic tube ends are adjusted and processed in order to allow the sealing items to be mounted- (self-sealing set, 8, or mounting nipple, 11), (pictures 2 and 3).

Pipe orientation changes can be achieved by using steel curves that have internal anticorrosive and anti-erosive protection by means of squirted plastics, made by welding together, at the steel tube level, modulated segments of curve protected on the inside (pictures 4 and 5), sealed at the plastic pipe level by means of joining elements, if necessary, with the self-sealing set, 8, or binding or welding, 12, plastic tubes (pictures 8 and 9). The entire range of pipe orientation changes required can be achieved by varying the number of segments, as well as the values of their sectioning angles from the tube axis.

Tightened joining between two elements of the pipe that can be straight sections, modulated curve segments or a straight pipe section and a modulated curve segment is achieved at squirted plastic tube level, 2, by means of a sealing set, 8, (picture 6), for non-uniform diameter pipes and by welding, 9, at steel tube level, 3 (picture 8).

In case you want to make steel pipes protected on the inside by squirted plastics, but with uniform internal diameter throughout the pipe (pipes that can be scraped), hermetic joining is achieved at squirted plastics level, along the straight segment, by means of mounting nipples, 11, (picture 7) and welding, 9, at steel tube level, (picture 9). The hermetic joining between the modulated segments forming a uniform internal diameter curve (pipes that can be scraped) is achieved at squirted plastic tube level, 2, by binding or welding, 12, and at steel segment level, 3, by welding, 9, (picture 9).

In order for the structure of the self-sealing set, 8, and of the mounting nipple, 11, materials to remain unaltered by the temperature of the steel tube, 3, welding area they are covered with a foliated ring, 10, made of a thermo-tolerant material.

There is a steel plate ring, 13, mounted over the plate ring, 10, so that it should result a steel support at the welding root, 9.

The steel pipes protected on the inside by means of squirted plastics against corrosion and erosion made according to the process described so far have the following characteristics : - its operation life is longer than steel pipe operation life, - it has high pressure resistance, thus allowing larger flows at the same diameter during exploitation, - higher resistance in the case of accidental internal or external stresses, - low capacity losses, due to the smooth internal surface, - there cannot appear any mineral scales on the internal surface, - the underground line does not require any special arrangements, - the plastic tube is safely sealed due to the sealing items used, the self-sealing set or the mounting nipple.