GB2209573A - Thread protector - Google Patents

Abstract

A protector for the thread of a bolt such as a bolt for use on under water structures, comprises a skirt 20 for locating over the nut 22, and a cap 16 for locating over the tip of the bolt 14. The cap 16 is internally threaded so that it may be tightened to press and seal against the upper wall 30 of the skirt 20, and press the skirt against the member 26 to form a seal between the member 26 and the flange 28. <IMAGE>

Description

Thread Protector The present invention relates to a thread protector for use in protecting the threaded tip of a bolt.

Structures which use nut-and-bolt fixings are sometimes used in hostile environments which may cause damage to the nut and/or bolt. Such hostile environments include corrosive chemicals and seawater. Offshore oil installations may incorporate many thousands of nut-andbolt fixings which are permanently underwater. Without protection, these nuts and bolts may quickly become corroded by the action of seawater until the nuts are difficult or impossible to remove for maintenance. Marine growth on the thread of the bolt may also hamper nut removal during routine maintenance.

It has previously been proposed to provide some protection to the thread of bolts by placing a push-fit plastic cap over the tip of the bolt, between the nut and the end of the bolt. The cap is slightly undersize so as to be held in position by the tightness of the fit. Caps have been found to reduce problems of marine growth but do not prevent corrosion. They tend to split during use because they are constantly under tension.

The present invention seeks to obviate or mitigate these and other disadvantages of the prior art.

According to the present invention there is provided a thread protector for use in protecting the threaded tip of a bolt, comprising a first cover portion having a recess for receiving the tip, the cover portion, in use, covering the end of the tip and a portion of the length of the tip, wherein the recess is internally threaded to engage, in use, the thread on the tip and to retain the cover portion on the tip.

The recess preferably has a mouth through which a tip may be received, the cover portion comprising a sealing surface around the mouth, whereby, in use, the cover portion may be threaded onto the tip until the sealing surface bears on a co-operating surface to provide a seal. The cover portion is preferably resiliently flexible to allow the cover portion to continue to be threaded onto the tip when the sealing surface is bearing on a co-operating surface, thereby tightening the sealing surface against the co-operating surface. The recess is preferably an internally threaded cylindrical bore which is closed at one end.

The protector preferably further comprises a second cover portion having a second recess for receiving a nut threaded on the bolt, the second recess forming part of a passage through the second cover portion through which the bolt tip may extend, whereby the second cover portion may be located, in use, over a nut and be held in position by abutment with the first cover portion. Preferably the second cover portion comprises a second sealing surface for co-operation with the sealing surface on the first cover portion, whereby, in use, a seal may be provided between the two cover portions. Preferably the second cover portion comprises a third sealing surface which, in use, is pressed against a surface against which the nut bears as the first cover portion is tightened on the bolt tip, to provide a seal between the said surface and the second cover portion.

Preferably the second cover portion is a cylindrical member having an open end and a partially closed end at which a generally transverse wall extends inwardly from the cylinder walls to define an aperture through which the bolt tip may extend. Preferably the transverse wall provides the second sealing surface. The transverse wall may be flexible and, in use, may flex as the first sealing surface is tightened against it, to provide a seal between the first and second cover members and between the transverse wall and the nut within the second recess.

Preferably the axial length of the second recess is greater than the axial length of the nut to be received wherein, and the second cover portion is flexible, whereby the second cover portion may flex as the first cover portion is tightened, to tighten the third sealing surface against the surface against which the bolt bears.

The second cover portion may comprise a flange around the open end of the second cover portion, the third sealing surface being provided on the flange. Preferably the third sealing surface is a generally frusto - conical surface which, in use and before the first cover portion is tightened, recedes from the surface against which the bolt bears towards the outermost edge of the third sealing surface, whereby a progressively larger region of the third sealing surface comes into contact with the surface against which the bolt bears, as the first cover portion is tightened.

Preferably the first and/or second cover portion is made from synthetic plastics material. The first and/or second cover portion may be moulded from polyurethane.

One embodiment of a protector will now be described in more detail, by way of example only, and with reference to the accompanying drawings in which Fig. 1 is a section through a protector according to the invention and in use; and Fig. 2 is a perspective view of the protector of Fig. 1.

The thread protector 10 shown in the drawings is for use in protecting the threaded tip 12 of a bolt 14. The protector 10 comprises a cover portion 16 or cap having an internally threaded bore forming a recess for receiving the tip 12. In use, as shown in Fig. 1, the cover 16 covers the end 18 of the tip 12 and a portion of the length of the tip 12. The cap is internally threaded to engage, in use, the thread on the tip 12 and retain the cap 16 on the tip 12.

The protector 10 further comprises a second cover portion 20 or skirt which has a recess for receiving a nut 22 threaded on the bolt 14. The recess in the skirt 20 and an aperture 24 together form a passage through the second cover portion through which the bolt tip 12 extends. The skirt 20 is located, in use, over the nut and held in position by abutment with the cap 16.

The cap 16 and skirt 20 are both cold moulded from polyurethane. This material can be accurately moulded, and is flexible and resistant to many corrosive substances, including seawater.

The skirt 20 has cylindrical side walls which may be circular in transverse section, or may be hexagonal to accommodate the nut 22 more tightly. The nut 22 is mounted on the bolt 14 to bear on a structural member 26.

The side walls of the skirt 20 widen at the end adjacent the member 26, to define a flange 28. The flange may narrow towards its outer edge, so that the lower face of the flange forms a frusto - conical surface. At the other end of the side walls, an annular wall 30 extends generally transverse from the side walls and defines the aperture 24. The diameter of the aperture 24 is less than the external diameter of the cap 16.

The cap 16 has circular cylindrical side walls which define the threaded internal bore which engages the bolt tip 12. Alternatively, the external surface of the cap side walls may be non-circular, such as hexagonal, to allow easier manipulation of the cap during installation.

The protector is used in the following manner. The bolt 14 and nut 22 are first assembled in the normal manner and the nut 22 tightened as required, to bear on the member 26. The skirt 20 is then placed over the tip 12, so that the tip projects through the aperture 24. The skirt 20 is then pushed along the bolt 14 until covering the nut 22. At this point, the flange 28 will be in abutment with the member 26, the skirt 20 being a loose fit over the nut 22.

Next, the cap 16 is threaded onto the projecting tip 12 until the annular surface around the mouth of the bore bears on the outer surface of the wall 30. Further tightening has two effects. The wall 30 around the aperture 24 is squeezed progressively more tightly between the cap 16 and the nut 22 and the flange 28 is pressed progressively more tightly against the member 26. As the cap is tightened, a progressively larger region of the frusto conical lower surface of the flange bears on the member 26. The flange 28 thereby forms a seal with the member 26 to prevent the ingress of seawater or other c orrosive material into the recess within the skirt 20, and the joint between the skirt 20 and cap 16 is similarly sealed by pressure. The cap and skirt thereby form a sealed cover over the whole of the tip 12 and nut 22.

The axial length of the skirt 20 may deliberately be greater than the axial length of the nut 22 to allow the wall 30 to flex as the cap 16 is tightened against it.

This, together with the overlength of the cap 16 and the flexibility of the material allows the components of the protector to be put into compression, thereby increasing the effectiveness of the seals, and provides a further seal between the edge of the wall 30 and the nut 22. The flexibility also allows minor variations in the surface flatness of the member 26 and the nut 22 to be accommodated without seals being broken.

In circumstances in which it is important to protect the thread of the bolt 14, but the nut 22 need not be protected against corrosion, the cap 16 may be used alone.

In this case, the cap 16 is tightened on the tip 12 until the annular surface around its mouth is tight against the surface of the nut 22 so providing a sealed cover around the peripheral portion of the tip 12 which projects beyond the nut 22.

It will be appreciated that variations and modifications may be made to the apparatus described without departing from the spirit of the present invention. Other materials may be chosen and differently shaped caps and skirts can be used. Provision may be made for more sophisticated seals but it is expected that the seals described above will be adequate for many situations and that it would be undesirable to increase the complexity and cost of manufacture of the article by incorporating further sealing components.

Claims (17)

1. A thread protector for use in protecting the treaded tip of a bolt, comprising a first cover portion having a recess for receiving the tip, the cover portion, in use, covering the end of the tip and a portion of the length of the tip, wherein the recess is internally threaded to engage, in use, the thread on the tip and to retain the cover portion on the tip.

2. A protector according to claim 1, wherein the recess has a mouth through which a tip may be received, the cover portion comprising a sealing surface around the mouth, whereby, in use, the cover portion may be threaded onto the tip until the sealing surface bears on a co-operating surface to provide a seal.

3. A protector according to claim 2, wherein the cover portion is resiliently flexible to allow the cover portion to continue to be threaded onto the tip when the sealing surface is bearing on a co-operating surface, thereby tightening the sealing surface against the co-operating surface.

4. A protector according to any of claims 1 to 3 wherein the recess is an internally threaded cylindrical bore which is closed at one end.

5. A protector according to any preceding claim, and further comprising a second cover portion having a second recess for receiving a nut threaded on the bolt, the second recess forming part of a passage through the second cover portion through which the bolt tip may extend, whereby the second cover portion may be located, in use, over a nut and be held in position by abutment with the first cover portion.

6. A protector according to claim 5, wherein the second cover portion comprises a second sealing surface for co-operation with the sealing surface on the first cover portion, whereby, in use, a seal may be provided between the two cover portions.

7. A protector according to claim 5 or 6, wherein the second cover portion comprises a third sealing surface which, in use, is pressed against a surface against which the nut bears as the first cover portion is tightened on the bolt tip, to provide a seal between the said surface and the second cover portion.

8. A protector according to any of claims 5 to 7, wherein the second cover portion is a cylindrical member having an open end and a partially closed end at which a generally transverse wall extends inwardly from the cylinder walls to define an aperture through which the bolt tip may extend.

9. A protector according to claim 8 and claim 6, wherein the transverse wall provides the second sealing surface.

10. A protector according to claim 9, wherein the transverse wall is flexible and, in use, flexs as the first sealing surface is tightened against it, to provide a seal between the first and second cover members and between the transverse wall and the nut within the second recess.

11. A protector according to any of claims 5 to 10, wherein the axial length of the second recess is greater than the axial length of the nut to be received therein, and the second cover portion is flexible, whereby the second cover portion may flex as the first cover portion is tightened, to tighten the third sealing surface against the surface against which the bolt bears.

12. A protector according to any of claims 5 to 11, wherein the second cover portion comprises a flange around the open end of the second cover portion, the third sealing surface being provided on the flange.

13. A protector according to claim 7 or any claim dependant thereon, wherein the third sealing surface is a generally frusto - conical surface which, in use, and before the first cover portion is tightened, receeds from the surface against which the bolt bears towards the outermost edge of the third sealing surface, whereby a progressively larger region of the third sealing surface comes into contact with the surface against which the bolt bears, as the first cover portion is tightened.

14. A protector according to any preceding claim, wherein the first and/or second cover portion is made from synthetic plastics material.

15. A protector according to claim 14, wherein the first and /or second cover portion is moulded from polyurethane.

16. A thread protector substantially as described above with reference to the accompanying drawings.

17. Any novel subject matter or combination including novel subject matter herein disclosed, whether or not within the scope of or relating to the same invention as any of the preceding claims.