Pressure-resistant Fiber Reinforced Hose

Abstract

A pressure-resistant hose, particularly for deep drilling, comprises spaced oppositely helically wound reinforcing inserts whose pitch, measured from a plane perpendicular to the axis of the hose, increases radially outwardly from insert to insert, for example, 6'--5.degree. for the innermost, 25--32.degree. for the next, and 38--45.degree. for the next outer layer.

Description

The present invention relates to a pressure-resistant fiber reinforced hose used primarily in deep drilling.

The hoses used in deep drilling are produced in their known form from a rubber tube surrounded by eventually prevulcanized rubberized textile layers, these textile layers being surrounded by wound metal wire or cable filaments, an intermediary textile layer with reinforcing insert or inserts and finally covered with protective textile and rubber layers. The subsequent reinforcing metal wire inserts are usually wound with the same pitch, but each insert is wound in opposite direction.

The pressure in the hose is borne mainly by the reinforcing inserts which are therefore subject to high stresses. The forces along the axes and tangents of the inserts vary in each insert because of the difference in the coil radii.

Under the influence of the different axial and tangential forces the inserts will show different elongation causing a shift in the relative positions of the turns of the inserted coils and the textile and rubber materials between the turns will suffer such high strains that they will break in a relatively short time under the loads and deloadings, that is under fatigue stress.

The tangential force is also different for each reinforcing coil, since each insert is placed over a different diameter.

Under the effect of the different tangential and axial forces the reinforcing coils will suffer a relative torsion causing a further increase of the strain on the textile and rubber layers between the coils thus accelerating their breakdown.

Since the ends of the hoses are fixed, the different elongations and torsions of the reinforcing insert coils hamper the cooperation between the reinforcing coils. Lack of cooperation and the different force effects in the fibers of the reinforcing insert coil result in loads much below their tensile strength on the filaments of some insert coils, while the filaments of some other insert coils would be loaded above their tensile strength and would break. Once one of the insert coils is broken the load on the other coils will rise suddenly leading to more breaks and the final break down of the hose.

To avoid this type of failure considerably more reinforcement is built into the hoses of known constructions than would be theoretically necessary when every insert coil filament were subjected to the same load below its tensile strength. As a result the known hose constructions are relatively heavy, expensive and rigid.

The object of the present invention is to produce hoses in which the strength of the reinforcements can be utilized uniformally and nearly equally under high pressure with full operational safety for a long period of time.

The object of the present invention is further to provide a pressure resistant fiber reinforced hoses whereby the strength of the reinforcing inserts is utilized to nearly 100 percent and the space requirement of the embedding textile layers is decreased in order to improve the pressure resistance of the hose without the application of more reinforcement, the cooperation of the reinforcing inserts is ensured for any pressure arising in the hose, and in addition the weight and wall thickness of the hose are reduced and its elasticity is improved.

According to the present invention these object is achieved by forming a hose in which the reinforcing insert material of the hose is divided into three or more, but preferably an uneven number of layers and said layers are wound up starting from the inside of the hose with pitches increasing from layer to layer from 6' to 50.degree..

According to one advantageous variation of the present invention two embedding textile layers are wound around the rubber tube, above which an auxiliary reinforcing insert of metal wire is wound with a pitch between 6' and 5.degree., this is covered by an intermediary textile layer, over which a reinforcing insert is wound in the same direction as the auxiliary insert with pitches between 25 and 32.degree., this is followed by a second intermediary textile layer and finally by a metal wire reinforcement wound in opposite direction to the first two reinforcements with pitches between 38 and 45.degree. and the hose is coated in the usual manner.

According to another advantageous variation the invention may be implemented by applying over the rubber tube and maximum two embedding textile layers an auxiliary reinforcing insert wound with pitches between 6' and 5.degree., above this a textile layer and again a reinforcing insert would in the same direction as the auxiliary reinforcement, but with pitches between 20 and 30.degree., covering this with a textile layer over which a second reinforcing insert is wound with pitches between 25 and 35.degree. in a direction opposite to the first two reinforcements, followed by a third reinforcing insert wound with pitches between 35 and 45.degree. and a fourth reinforcing insert wound with pitches between 40 and 50.degree. and by finally covering the hose in the usual manner.

The hose according to the present invention was constructed in accordance with the concept that a hose can be in stress equilibrium only if the tangential pressure resistance of an insert or inserts wound in one direction is in equilibrium with the axial pressure resistance of an insert or inserts wound in opposite direction and vice versa, that is

P.sub.tl = P.sub.a2 and P.sub.t2 = P.sub.a1

where

P.sub.t is the tangential pressure resistance and P.sub.a the axial pressure resistance.

The basic condition for the cooperation and equal stress conditions of the inserts is the equality of the longitudinal relative changes of the inserts, that is, of the longitudinal forces arising in the inserts, since the ends of the hose and thus of the inserts are fixed by some rigid terminals.

From the relative diameter changes of inserts with two different diameters in a pair of inserts ideal .beta..sub.1 and .beta..sub.2 pitches can be determined for each insert which will ensure that the two inserts shall be in nearly identical stress conditions at any arbitrary internal pressure and shall be capable of cooperation. The winding angle of the insert is determined from the changes in length and diameter of the fiber due to its elongation.

To realize perfect stress symmetry, that is fully equal stresses on the inserts in accordance with the present invention an auxiliary insert is applied in addition to the pair or pairs of inserts; the tangential and axial pressure resistance of this auxiliary insert supplements the corresponding pressure resistance of the other inserts. This auxiliary insert is wound under the first reinforcing insert in the same direction as the latter.

This auxiliary insert has practically only a tangential pressure resistance, that is it is wound with a very low pitch, but ties the rubber hose with its minimum, not more than two layers textile covering firmly down and is useful for the circular embedding of the two or more reinforcing inserts.

The more essential advantages of the invention are the following:

It ensures the equal stress of an insert system consisting of three or more uneven number of inserts; it enhances the strength of the reinforcement in a measure hitherto not observed.

The third insert of preferably a single filament wound with a very low pitch on the rubber tube or on the not more than two textile layers covering the rubber tube serves as a rigid embedding for the winding of the strong insert layers which eliminates the bulky textile embedding of several layers used hitherto. The main reinforcing inserts are situated on a smaller diameter which reduces the quantity needed of the reinforcing insert material while the pressure resistance of the inserts increases.

The third auxiliary insert participates fully in the pressure resistance and pressure symmetry of the hose and in addition is capable of adjusting itself fully to the equal stress conditions of the main inserts.

The invention will be further described, by way of example, with reference to the accompanying drawings, in which:

FIG. 1 is a longitudinal section of a hose of known construction with two inserts;

FIG. 2 is a longitudinal section of a hose with 2+1 inserts produced according to the present invention; and

FIG. 3 is a longitudinal section of a hose with 4+1 inserts according to the invention.

The hose shown in FIG. 1 consists of a rubber tube 1, several rubberized textile embedding layers 2, a first reinforcing insert 3, a rubberized textile layer 4 between the reinforcements, a second reinforcing insert 5, protective rubberized textile layer 6 and a covering rubber layer 7.

In FIG. 2 the reference numerals stand for the same types of components, with the exception that here a single embedding textile layer 2 was used with an auxiliary reinforcing insert 8 above it and an embedding rubberized textile layer 9 above the insert 8.

The hose in FIG. 3 consists of a rubber tube 1, embedding textile layers 2, reinforcing inserts 3a and 3b and 5a and 5b, textile layers 4a, 4b and 4c between the reinforcing inserts, auxiliary reinforcing insert 8 with embedding textile layer 9 above it, rubberized protective textile layer 6 and covering layer 7.

One hose according to FIG. 2 of the present invention was constructed of the following layers:

Rubber tire 4.0 mm.

One layer rubberized textile 0.5 mm.

Auxiliary insert 0.9 mm.

Textile layer between inserts 0.5 mm.

First reinforcing insert (cable) 2.8 mm.

Textile layer between inserts 0.5 mm.

Second reinforcing layer (cable) 2.8 mm.

Two rubberized textile protective layers 2.0 mm.

Outer protective rubber layer 2.0 mm.

The mean diameter D of the three inserts and the pitches .beta. of the inserts were as follows:

Auxiliary insert D.sub.o = 8.59 cm. .beta..sub.o = 0.5.degree.

First reinforcing insert D.sub.1 = 9.06 cm. .beta..sub.1 = 30--55.degree.

Second reinforcing insert D.sub.2 = 9.72 cm. .beta..sub.2 = 41--45.degree.

As will be seen from a comparison of the layers 8 and 3 in FIG. 2 (and 8 and 3a in FIG. 3) the recited pitch angles are measured from planes perpendicular to the axis of the hose.

With this construction the calculated pressure resistance of the hose is 898 kp/cm..sup.2 while the hose made of the same materials but in the customary form by the known method, thus without auxiliary insert, by winding the two reinforcing insert with a pitch of 35.degree.16' and by applying over the rubber tube four textile layers for embedding broke down at 680 kp/cm..sup.2 internal pressure.

Claims

I claim:

1. A pressure-resistant hose comprising a rubber tube with multilayered embedding and intermediary textile layers and reinforcing inserts and a covering rubber coat, comprising at least two helically wound reinforcing inserts having a pitch increasing from the axis of the hose towards the covering coat from layer to layer, as measured from a plane perpendicular to the axis of the hose, in such a way that the reinforcing inserts satisfy the formulas:

Pt.sub.1 = P a.sub.2 and P t.sub.2 = P a.sub.1 wherein

Pt.sub.1 is the tangential pressure resistance of a first insert wound in one direction;

Pa.sub.2 is the axial pressure resistance of a second insert wound in the opposite direction;

Pt.sub.2 is the tangential pressure resistance of said second insert; and

Pa2 is the axial pressure resistance of said first insert.

2. Hose according to claim 1, and an auxiliary reinforcing insert wound helically under the reinforcing inserts with a pitch between 6' and 5.degree. as measured from a plane perpendicular to the axis of the hose.

3. Hose according to claim 1, wherein the pitch of the first reinforcing insert is between 25 and 32.degree. and the pitch of the second reinforcing insert is between 38 and 45.degree. as measured from a plane perpendicular to the axis of the hose.

4. A hose according to claim 1, comprising four reinforcing inserts, wherein the first reinforcing insert has a pitch between 20 and 30.degree., the second reinforcing insert is wound in opposite direction with a pitch between 25 and 35.degree., the third reinforcing insert is wound in the same direction as the first reinforcing insert, with a pitch between 35 and 45.degree., and the fourth reinforcing insert is wound in the same direction as the second reinforcing insert with a pitch between 40 and 50.degree..

5. A hose according to claim 1 wherein the reinforcing inserts are metal wires.