Reinforcing member and an article, such as a pressure vessel, containing the reinforcing member

Abstract

The invention relates to a reinforcing liner comprising load-bearing yarns of a first type characterized in that the liner further comprises load-bearing yarns of a second type having a creep rate {acute over ()}.sub.2 of at least 10 times higher than the creep rate {acute over ()}.sub.1 of the yarns of first type, i.e. {acute over ()}.sub.210{acute over ()}.sub.1, wherein the creep rates are measured on the yarns at a temperature of 20 C. and under an applied load of 600 MPa. The invention also relates to a pressure vessel comprising thereof.

Claims

1. A reinforcing member comprising first and second types of load-bearing yarns, wherein the first type of load-bearing yarns have a creep rate {acute over ()}.sub.1 and are comprised of a first type of continuous filaments, and wherein the second type of load-bearing yarns have a creep rate {acute over ()}.sub.2 and are comprised of a second type of continuous filaments, and wherein the creep rate {acute over ()}.sub.2 of the second type of load-bearing yarns is at least 10 times higher than the creep rate {acute over ()}.sub.1 of the first type of load-bearing yarns to thereby satisfy a relationship:
{acute over ()}.sub.210{acute over ()}.sub.1 wherein the creep rates {acute over ()}.sub.1 and {acute over ()}.sub.2 are measured on the first and second types of load-bearing yarns, respectively, at a temperature of 20 C. and under an applied load of 600 MPa.

2. The reinforcing member of claim 1, wherein the first type of load-bearing yarns are polymeric yarns.

3. The reinforcing member of claim 1, wherein the second type of load-bearing yarns are polymeric yarns.

4. The reinforcing member of claim 1, wherein the creep rate {acute over ()}.sub.2 is at least 30 times higher than the creep rate {acute over ()}.sub.1.

5. The reinforcing member of claim 1 wherein the creep rate {acute over ()}.sub.2 is at least 10.sup.9 sec.sup.1 and the creep rate {acute over ()}.sub.1 is at most 10.sup.8 sec.sup.1.

6. The reinforcing member of claim 1, wherein the first type of load-bearing yarns have a fracture strain F.sub.1, and the second type of load-bearing yarns have a fracture strain F.sub.2, and wherein a ratio F.sub.1/F.sub.2 is between 1.1 and 6.

7. The reinforcing member of claim 1, wherein the first type of load-bearing yarns are manufactured from aromatic copolyamide prepared from terephthaloyl chloride and equimolar proportions of p-phenylenediamine and 3,4-diaminodiphenylether, and the second type of load-bearing yarns are manufactured from ultra high molecular weight polyethylene (UHMWPE).

8. The reinforcing member of claim 1 wherein the first type of load-bearing yarns contained by the member are present in the member in a mass % amount of between 20% and 80% based on total mass of the first and second types of load-bearing yarns.

9. The reinforcing member of claim 1 further comprising a resin.

10. The reinforcing member according to claim 1 wherein the member is a liner.

11. The reinforcing member of claim 1, wherein each of the first and second types of load-bearing yarns have a linear configuration.

12. The reinforcing member of claim 1, wherein the second load-bearing yarns elongate by creep under a tension force at which strain induced in the first type of load-bearing yarns is about equal to fracture strain of the first type of load-bearing yarns.

13. A pressure vessel comprising the member of claim 1.

14. A pressure vessel having a vessel wall reinforced with the member of claim 1, wherein the second type of load-bearing yarns are elongated by creep under a stress induced by deformation of the vessel wall achieved by pressurizing the vessel at a pressure of at most a pressure at which strain induced in the first type of load-bearing yarns is about equal to fracture strain of the first type of load-bearing yarns.

15. The pressure vessel of claim 11, wherein the pressure vessel is a pipe.

16. An article comprising a member according to claim 1, wherein the article is selected from the group consisting of a rope, a suture, a cable, a sling, a composite, a liner, and a chain construction.

17. The article of claim 16, wherein the member increases efficiency of the article to above 100%.

Description

(1) Hereinafter the figures are explained.

(2) FIG. 1 represents a strain vs. pressure (strain-pressure) diagram of a pressurized vessel.

(3) FIG. 2 is a schematic representation of the device used for creep measurements. The illustrations (1) and (2) represent an instance of the yarn length (200) at the beginning of the experiment and an instance of the elongated yarn after a certain time t, respectively.

(4) FIG. 3 shows a plot of the creep rate [1/s] on a logarithmic scale vs. the elongation in percentage [%] characteristic to a measured yarn.

TEST EQUIPMENT AND METHODS

(5) The strain induced in the load-bearing yarns by the load exerted by the working pressure to which the pressure vessel is subjected was determined with common strain gauges mounted in both radial and longitudinal direction on the walls of the vessel. Such strain gauges are commercially available. Stress-strain (or pressure-strain) diagram of the pressurized vessel was recorded by pressurizing the heated vessel at 70 C. to about 20% of the initial bursting pressure at a pressure rate such that the mentioned pressure is reached in about 2 minutes, and then keeping that pressure for 1 month. The pressure is then released with the same rate used as when it was applied. The strain induced in the vessel by pressurization was measured with strain gauges. A schematic representation of the recorded diagram (700) of the measured strain (702) vs. the applied pressure (701) is shown in FIG. 1. During the 2 minutes of initial pressure application, a linear increase (703) in strain with pressure was observed. Following stopping the application of the pressure (704) and during keeping the vessel for 1 month at 70 C. to the applied pressure, a strain increase at constant pressure (705) was measured by the strain gauges. After 1 month (706) of keeping the vessel under pressure, the pressure was released over 2 minutes and during the depressurization of the vessel, the strain decreased linear with the pressure in two stages. A first stage (707) where the decrease is almost parallel with the initial increase (703), which shows that both types of yarns under tension were released; and a second stage (708) where the decrease is faster, which shows that the second type of yarns (the high creep yarn) was no longer under tension and only the tension of the first type of yarns under tension was released. The proof that the type 2 yarns were elongated by creep is the presence of part (705) in the diagram wherein the strain increases at constant pressure. Fracture strain of yarns was determined in about 2 minutes according to the commonly known and used ISO-2062. The initial bursting pressure of a pressure vessel was measured by pressurizing the vessel at yet higher pressures in about 2 minutes until the vessel fractured releasing the pressure. The pressure at the moment of fracturing was considered as the bursting pressure. The bursting pressure after a certain time (usually and in the following examples 1 month) of the pressure vessel was measured at an elevated temperature (70 C.) by pressurizing the vessel for the certain time (usually 1 month) and then rapidly increasing the pressure until the vessel fractured releasing the pressure. The efficiency was calculated as the ratio between the bursting pressure after the certain time and the initial bursting pressure. Hence, an efficiency of 100% means that the bursting pressure after one month at a pressure of 20% of the initial bursting pressure is the same as the initial bursting pressure. An efficiency of more than 100% means that the bursting pressure has increased after one month at a pressure of 20% of the initial bursting pressure, and an efficiency of less than 100% (which is the expected result) means that the bursting pressure has decreased after one month at a pressure of 20% of the initial bursting pressure. Creep rate was measured according to the methodology described hereinafter.

(6) Creep tests were performed with a device as schematically represented in FIG. 2, on untwined yarn samples, i.e. yarn with substantially parallel filaments, of about 1500 mm length, having a titer of about 504 dtex and consisting of 64 filaments.

(7) The yarn samples were slip-free clamped between two clamps (101) and (102) by winding each of the yarn's ends several times around the axes of the clamps and then knotting the free ends of the yarn to the yarn's body. The final length of the yarn between the clamps (200) was about 180 mm.

(8) The clamped yarn sample was placed in a temperature-controlled chamber (500) at a temperature of 70 C. by attaching one of the clamps to the sealing of the chamber (501) and the other clamp to a counterweight (300) of 3162 g resulting in a load of 600 MPa on the yarn. The position of the clamp (101) and that of clamp (102) can be read on the scale (600) marked off in centimeters and with subdivisions in mm with the help of the indicators (1011) and (1021).

(9) Special care was taken when placing the yarn inside said chamber to ensure that the segment of the yarn between the clamps does not touch any components of the device, so that the experiment can run fully friction free.

(10) An elevator (400) underneath the counterweight was used to raise the counterweight to an initial position whereat no slackening of the yarn occurs and no initial load is applied to the yarn. The initial position of the counterweight is the position wherein the length of the yarn (200) equals the distance between (101) and (102) as measured on (600).

(11) The yarn was subsequently preloaded with the full load of 600 MPa during 10 seconds by lowering the elevator, after which the load was removed by raising again the elevator to the initial position. The yarn was subsequently allowed to relax for a period of 10 times the preloading time, i.e. 100 seconds.

(12) After the preloading sequence, the full load was applied again. The elongation of the yarn in time was followed on the scale (600) by reading the position of the indicator (1021). The time needed for said indicator to advance 1 mm was recorded for each elongation of 1 mm until the yarn broke.

(13) The elongation of the yarn .sub.i [in mm] at a certain time t is herein understood the difference between the length of the yarn between the clamps at that time t, i.e. L(t), and the initial length (200) of the yarn L.sub.0 between the clamps. Therefore:
.sub.i(t)[in mm]=L(t)L.sub.0
The elongation of the yarn [in percentages] is:

(14) ${\mathrm{.Math.}}_i\left(t\right)\left[\mathrm{in}\%\right]=\frac{L\left(t\right)-L_0}{L_0}100$
The creep rate [in 1/s] is defined as the change in yarn's length per time step and was determined according to Formula (2) as:

(15) $\begin{array}{cc}{\stackrel{.}{\mathrm{.Math.}}}_i=\frac{{\mathrm{.Math.}}_i-{\mathrm{.Math.}}_{i-1}}{t_i-t_{i-1}}\frac{1}{100}& \left(2\right)\end{array}$
wherein .sub.i and .sub.i-1 are the elongations [in %] at moment i and at the previous moment i1; and t.sub.i and t.sub.i-1 are the time (in seconds) needed for the yarn to reach the elongations .sub.i and .sub.i-1, respectively.

(16) The creep rate [1/s] was then plotted on a logarithmic scale vs. the elongation in percentage [%]. An example of such a recorded plot characteristic to a gelspun UHMWPE yarn is shown in FIG. 3.

(17) The minimum (e.g. (900) in FIG. 3) of the plot was then used as the creep rate value characteristic to the investigated yarn.

EXAMPLE AND COMPARATIVE EXPERIMENT

Example

(18) A high density polyethylene (HDPE) pipe of 8 diameter, 5 mm wall thickness and 1.5 m length was reinforced with a member in the form of a liner consisting of yarns of first type and second type by winding the liner around the pipe under an angle of about 54.7 with respect to the axial direction of the pipe. The pipe was pressurized at a pressure of 25% of bursting pressure.

(19) The yarns of first type were manufactured from an aromatic copolyamide prepared from terephthaloyl chloride and equimolar proportions of p-phenylenediamine and 3,4-diaminodiphenylether. Such yarns are commercially available under the name Technora being produced by Teijin. The yarns had a titer of 1670 dtex, a fracture strain of 4.6% and a strength of 24.7 cN/dtex.

(20) The yarns of second type were HPPE yarns manufactured from UHMWPE by a gel spinning technique. Such yarns are commercially available under the name DyneemaSK75 being produced by DSM Dyneema, the Netherlands. The yarns had a titer of 1760 dtex, a fracture strain of 3.5% and a strength of 35.1 cN/dtex.

(21) An equal number of yarns of first and second type was used, the mass % of yarns is of first type being 48.7 and of the second type 51.3.

(22) The efficiency of the pipe was 130%, where 100% corresponds to the initial burst strength.

Comparative Experiment

(23) Example was repeated but the liner consisted of only Technora yarns.

(24) The efficiency of the pipe was 90%.

(25) It can be seen from the above experimental data that the efficiency of a pressure vessel comprising a member according to the invention increases in time whereas the efficiency of a known pressure vessel always decreases with time. Therefore, a pressure vessel of the invention has an increased safety factor and most surprisingly, the safety factor increases with time.