Protection system for a threaded fastener and a method for installation, inspection and maintenance of such protection system

Abstract

A protection system for a threaded fastener is provided. The system includes a threaded fastener, a sleeve and either two end caps, or one end cap and one threaded hole in a component. To avoid exposure to severely corrosive environments the sleeve and either the two end caps, or the one end cap and the one threaded hole, together form an enclosure around the threaded fastener. The enclosure forms a cavity which is completely sealed from the environment. Furthermore, methods are described for mounting, inspection and maintenance of such protection system.

Claims

1. A protection system for a threaded fastener, the protection system comprising: a threaded fastener comprising a shank, a first end, and a second, a sleeve, and either two end caps covering the first end and the second end, or one end cap covering the first end and one component with a threaded bottom hole into which the second end of the threaded fastener is screwed, the one component being different from a nut, wherein the sleeve together with either the two end caps, or together with the one end cap and the threaded bottom hole of the one component, form an enclosure around the threaded fastener, wherein a sealing ring is provided, the sealing ring comprising an inner O-ring and an outer O-ring, the outer O-ring having a larger diameter than the inner O-ring, wherein the inner O-ring extends around the sleeve in abutment with the sleeve for forming an inner sealing that seals against the sleeve and wherein the outer O-ring forms an outer sealing that seals the sealing ring against a respective end cap such that the enclosure forms a cavity completely sealed from an environment.

2. The protection system for a threaded fastener according to claim 1, wherein the cavity is partly or completely filled with a corrosion-protective substance, wherein said corrosion-protective substance is a corrosion-protecting oil or grease.

3. The protection system for a threaded fastener according to claim 1, wherein the shape and/or material of part of or the whole respective end cap is sufficiently flexible to ensure that any external pressure gives rise to an approximately equal internal pressure.

4. The protection system for a threaded fastener according to claim 1, wherein part of or the whole respective end cap is shaped as a bellows.

5. The protection system for a threaded fastener according to claim 1, wherein part of or the whole respective end cap is manufactured from an elastomeric material.

6. The protection system for a threaded fastener according to claim 1, wherein at least one of the respective end cap, the sleeve and the sealing ring is fitted with an inlet, wherein the inlet is a grease nipple for the filling with a corrosion-protective substance.

7. The protection system for a threaded fastener according to claim 1, wherein there is provided a washer around the sleeve at an end of the threaded fastener, wherein the sleeve and the washer are electrically insulating.

8. The protection system for a threaded fastener according to claim 1, wherein the sealing ring comprising an inner groove in which the inner O-ring is provided and an outer groove in which the outer O-ring is provided.

9. The protection system for a threaded fastener according to claim 1, wherein the sealing ring comprises an outer threading and the end cap comprises a corresponding inner threading, wherein the inner threading is screwed onto the outer threading of the sealing ring for fastening the end cap onto the sealing ring.

10. A method for mounting of a protection system for a threaded fastener, the protection system comprising a threaded fastener including a shank, a first end, and a second end, a sleeve, and either two end caps for covering the first end and the second end, or one end cap for covering the first end and one component with a threaded bottom hole into which the second end of the fastener is screwed, the one component being different from a nut, wherein the method comprises the following steps: fitting the threaded fastener into the sleeve; providing a sealing ring between the sleeve and a respective end cap, wherein the sealing ring comprises an inner O-ring and an outer O-ring, the outer O-ring having a larger diameter than the inner O-ring; wherein the inner O-ring extends around the sleeve in abutment with the sleeve for forming an inner sealing that seals the sealing ring against the sleeve and wherein the outer O-ring forms an outer sealing that seals the sealing ring against the respective end cap; and forming an enclosure around the threaded fastener, the enclosure comprising the sleeve and either the two end caps or the one end cap and the threaded bottom hole of the one component, such that the enclosure forms a completely sealed from an environment.

11. A protection system for a threaded fastener, wherein the threaded fastener comprises a first threading at a first end of the fastener, and a threaded nut screwed onto the first threading; wherein the protection system comprises: a cylindrical sleeve provided around a shank but not extending around the threaded nut, the cylindrical sleeve having an outer cylindrical surface; an end cap having a cavity accommodating the first end and the threaded nut; an inner O-ring provided between the end cap and the cylindrical sleeve and extending around the cylindrical sleeve in abutment with an outer cylindrical surface for forming an inner sealing that seals the end cap against the cylindrical sleeve; wherein the protection system comprises a sealing ring, wherein the sealing ring comprises the inner O-ring and an outer O-ring, the outer O-ring having a larger diameter than the inner O-ring; wherein the inner O-ring forms an inner sealing that seals the sealing ring against the cylindrical sleeve and wherein the outer O-ring forms an outer sealing that seals the sealing ring against the end cap.

12. The protection system for a threaded fastener according to claim 11, wherein the sealing ring comprises an inner groove in which the inner O-ring is provided and an outer groove in which the outer O-ring is provided, the outer groove and the outer O-ring having a larger diameter than the inner groove and the inner O-ring.

13. The protection system for a threaded fastener according to claim 11, wherein the sealing ring comprises an outer threading and the end cap comprises an inner threading, wherein the inner threading is screwed onto the outer threading of the sealing ring for fastening the end cap onto the sealing ring.

14. The protection system for a threaded fastener according to claim 11, wherein the cylindrical sleeve is electrically insulating, and wherein the protection system further comprises an electrically insulating washer abutting the sealing ring on an opposite side of the sealing ring relative to the end cap.

Description

BRIEF DESCRIPTION

(1) Some of the embodiments will be described in detail, with reference to the following figures, wherein like designations denote like members, wherein:

(2) FIG. 1 illustrates a protection system for a threaded fastener according to embodiments of the invention;

(3) FIG. 2 illustrates the protection system for a threaded fastener depicted in FIG. 1 in more detail;

(4) FIG. 3 illustrates an embodiment of the protection system for a threaded fastener as applied when the threaded fastener is installed in a bottom hole;

(5) FIG. 4a illustrates an embodiment of the protection system for a threaded fastener with a pressure-balancing feature;

(6) FIG. 4b illustrates an embodiment of the protection system for a threaded fastener with a pressure-balancing feature;

(7) FIG. 5a illustrates an embodiment of the protection system for a threaded fastener with a pressure-balancing feature and supplementary protection;

(8) FIG. 5b illustrates an embodiment of the protection system for a threaded fastener with a pressure-balancing feature;

(9) FIG. 6 illustrates an embodiment of the protection system for a threaded fastener with the end cap and the sealing ring integrated with the nut; and

(10) FIG. 7 illustrates an embodiment of the protection system for a threaded fastener with a pressure-balancing feature and supplementary protection and where the end cap and the sealing ring are integrated with the nut.

DETAILED DESCRIPTION

(11) In the figures, similar or corresponding elements are denoted with the same reference numerals.

(12) FIG. 1 illustrates a protection system for a threaded fastener according to embodiments of the invention. A threaded fastener 1 is mounted through two flanges 2 and 3. The threaded fastener is fitted with an extender 4 which allows the use of a fastener that is longer than the combined thickness of the flanges, thereby reducing the risk of loss of pretension because of settling of the assembly and relaxation of the materials. At one end the threaded fastener has a head 5 and at the other end a nut 6 is fitted.

(13) FIG. 2 illustrates the protection system for a threaded fastener depicted in FIG. 1 in more detail. Under the nut 6 a hardened washer 7 is mounted. The washer 7 rests on a sealing ring 8 and an insulating washer 9, which rests against the extender 4. Around the shank 10 of the fastener 1 an insulating sleeve 11 is fitted. The insulating sleeve 11 fits into an O-ring seal 12 in the sealing ring 8. On the outside of the sealing ring an end cap 13 is fitted. The end cap 13 comprises a threaded ring 14 and an end cap cover 15. The threaded ring 14 forms a seal with an O-ring 16 mounted in the sealing ring 8.

(14) In this arrangement the threaded fastener 1 is completely protected against the environment. Consequently, it may be a “black”, unprotected threaded fastener, such as a conventional class 8.8 or 10.9 threaded fastener. Equally, the nut 6 may be a “black”, unprotected nut, such as a class 8 or 10 nut, and the hardened washer 7 may also be a simple, “black”, unprotected hardened washer made of carbon steel. The sealing ring 8 and the end cap 13 comprising the threaded ring 14 and the end dap cover 15 may be made of a variant of Alloy 625 metal, such as Inconel, or of some other material immune to corrosion. The threaded ring 14 and the end dap cover 15 may be manufactured as separate components, joined by laser welding. The insulating washer 9 and the insulating sleeve 11 may be made of GRP. The O-rings 12 and 16 may be made of nitrile rubber. The cavity 17 inside the end cap 13 and the sleeve 11 may be air-filled, or it may be partly or completely filled with a corrosion-protective substance such as corrosion-protecting oil or grease.

(15) FIG. 3 illustrates an embodiment of the protection system for a threaded fastener as applied when the fastener is installed in a bottom hole. The fastener 1 is screwed into a threaded hole 18 machined into a component 19, such as a flange. The insulating sleeve 11 fits into an O-ring seal 12 in the component 19.

(16) FIG. 4 illustrates an embodiment of the protection system for a threaded fastener with a pressure-balancing feature. Here the end cap 13 comprises a threaded ring 14 and an end cap cover 15 shaped as a bellows. The end cap cover 15 is fitted with a grease nipple 20. FIG. 4.a shows the protection system after the threaded ring 14 of the end cap 13 has been fitted to the sealing ring 8 and before any supplementary corrosion-protective substance has been added. The bellow-shaped end cap cover 15 is substantially in its neutral position. FIG. 4.b shows the protection system after a desired amount of supplementary corrosion-protective substance has been added through the grease nipple 20. The bellow-shaped end cap cover 15 is now in its extended position, exerting a small pressure on the corrosion-protective substance in the cavity 17.

(17) FIG. 5 illustrates embodiments of the protection system for a threaded fastener with a pressure-balancing feature and supplementary protection, where the supplementary protection is integrated with the end cap. Here the end cap 13 comprises a threaded ring 14, a protective cover in the form of a tubular member 21, and a bellows 22 joined to the inside of the tubular member 21. The tubular member 21 has an internal ring 23 that acts as an end stop for the bellows 22, limiting the extent to which the bellows 22 can extend because of being filled with supplementary corrosion-protective substance through the grease nipple 20. The tubular member 21 extends somewhat beyond the internal ring 23 to a rim 24 that provides protection for the bellows 22 and the grease nipple 20. FIG. 5.a shows the protection system after the threaded ring 14 of the end cap 13 has been fitted to the sealing ring 8 and before any supplementary corrosion-protective substance has been added. The bellow 22 is substantially in its neutral position. FIG. 5.b shows the protection system after a desired amount of supplementary corrosion-protective substance has been added through the grease nipple 20. The bellow 22 is now in its extended position, resting against the internal ring 23 of the tubular member 21, exerting a small pressure on the corrosion-protective substance in the cavity 17. The condition of the protection system can be readily verified by visual inspection of the position of the grease nipple 20 relative to the internal ring 23 and/or the rim 24 of the tubular member 21.

(18) FIG. 6 illustrates an embodiment of the protection system for a threaded fastener where the end cap 13 is integrated with the nut 6 and the sealing ring 8. In this embodiment the O-ring 12 which seals against the sleeve 11 is fitted into the integrated sealing ring 8, and the metallic washer 7 rests directly on the insulating washer 9. The cavity 17 may be air-filled or partly or completely filled with another substance, such as a corrosion-protective substance. The end cap 13 may be fitted with a grease nipple 20 (not shown on the drawing).

(19) FIG. 7 illustrates an embodiment of the protection system for a threaded fastener where the end cap 13 is integrated with the nut 6 and the sealing ring 8, and which has pressure compensation. In this embodiment the end cap 13 is integrated with a protective cylinder 21 that is extended to form a rim 24 that provides protection for a piston 25 fitted with a grease nipple 20. The piston 25 is pushed towards the end face of the nut 6 by a spring 26 kept in place by a locking ring 27. The piston is sealed against the inside of the cylinder 21 by two O-rings 28. The force from the spring 26 maintains an overpressure on a corrosion-protective substance in the cavity 17. After the nut 6 has been tightened on the fastener 1 supplementary corrosion-protective substance has been added through the grease nipple 20 until the spring 26 has been pressed to its fully compressed position. The condition of the protection system can be readily verified by visual inspection of the position of the grease nipple 20 relative to the rim 24 of the cylindrical part 21 of the end cap 13.

(20) In the following several constructional details are specified for the protection system.

(21) The pressure in the cavity (17) inside the sleeve (11) and the end cap (13) is maintained at a level that is higher than the ambient pressure.

(22) The elastic, spring-like properties of the end cap (13) are used to maintain the pressure in the cavity (17) inside the sleeve (11) and the end cap (13) at a level that is higher than the ambient pressure.

(23) The elastic properties of mechanical or gaseous springs are used to maintain the pressure in the cavity (17) inside the sleeve (11) and the end cap (13) at a level that is higher than the ambient pressure.

(24) The end cap (13) is partly or completed surrounded by a protective cover (21).

(25) The protective cover (21) is integrated with the end cap (13).

(26) The protective cover (21) is used to maintain the sealing and position of the end cap (13).

(27) The protective cover (21) provides an end stop (23) for the flexible part of the end cap (13).

(28) In the following several specific steps are specified for the method.

(29) A pressure in the cavity (17) inside the sleeve (11) and the end cap (13) is established at a level that is higher than the ambient pressure.

(30) The pressure in the cavity (17) inside the sleeve (11) and the end cap (13) is established by the introduction of a fluid substance such as a corrosion-protective substance into the cavity (17) through inlet means in the end cap (13), the sleeve (11) and/or any sealing ring (8).

(31) Increasing the pressure in the cavity (17) inside the sleeve (11) and the end cap (13) to a level that expands the end cap (13) to a pre-defined dimension or shape.

(32) Although the present invention has been disclosed in the form of preferred embodiments and variations thereon, it will be understood that numerous additional modifications and variations could be made thereto without departing from the scope of the invention.

(33) For the sake of clarity, it is to be understood that the use of “a” or “an” throughout this application does not exclude a plurality, and “comprising” does not exclude other steps or elements. The mention of a “unit” or a “module” does not preclude the use of more than one unit or module.