IPELINE OR VESSEL

The present invention is concerning an access fitting for attaching a device within a process pipeline or vessel as described in the introductory part of claim 1.

In further detail, the present invention relates to a sealing- and preload method for a conical plug in a pipe fitting. The plug is in itself a conventional and accepted way of sealing a pipe fitting. More specifically, the invention covers a novel sealing device which intends to increase sealing efficiency and safety, with better lateral support to both the plug itself and possible extensions mounted to it.

Background

Conical plugs in pipe fittings have become widely used in the oil-, gas- and process industries, e.g. to seal off various devices such as probes for measuring and monitoring purposes. Examples of this are the ER or LPR probes or weight-loss coupons which are mounted into process vessels, wellheads or water injection systems. By using a fitting provided with internal threads and a plug provided with external threads, a probe can be inserted into a pipe to become in direct contact with the process medium, while being sealed off with a preload from said threads acting on a conical seal between plug and fitting. Another way to preload the conical seal is with the clamping force of a cover nut with internal threads, matching an outside such on the fitting.

Both methods above lack sealing efficiency, requires high preload, has no built-in secondary- seal safety and gives poor support to plug extensions such as a measuring probe described above.

A conventional seal for a conical plug is typically an annular packing made from a polymer material such as fiber-reinforced PTFE. Said packing needs to be preloaded through an axial force applied on the plug, all in order to overcome the counter-force from the line-pressure inside the pipe on the opposing side of the plug. With a line-pressure of more than 400 bar and

a packing diameter of 40 mm, the counter-force can be as much as 50 kN or five metric tons. Needless to say, the axial force on the plug should be considerably higher than the expected counter-force in order to provide a margin against leakage, which calls for a massive torque, as much as 1000 Nm, to be applied on either the large diameter threaded plug or threaded cover in the solutions described above. Moreover, in case of a seal failure, a separate secondary seal must be applied up-streams for safety reasons.

Another problem is that all external forces on the plug coming from mentioned extensions passes through the PTFE packing, which has a low stiffness in itself even if preloaded, leading to leakage and possible problems with natural frequencies on long measuring probes.

Object The object of the present invention is therefore to provide an access fitting for attaching a device within a process pipeline or vessel that increases sealing efficiency and safety, reduces torque needed for necessary preload and improves the device's lateral stiffness. The invention

The object of the present invention is achieved by an attachment fitting for attaching a device within a process pipeline or vessel as described in the characterizing part of claim 1. Further advantageous features appear from the respective dependent claims.

The surprising technical effect is achieved by a combination of a radially compliant and self- energized seal, and a plurality of low-torque bolts acting directly on the device, preloading the latter with a conical metal-to-metal contact directly against the fitting.

The term "device" is here meant to include any physical device which is accommodated within the access fitting, temporarily as well as permanent. Examples of devices of this type are: devices for sample extraction from the interior of the pipeline or vessel, devices for injection of chemicals, a weight loss coupon for measuring corrosion within the pipeline or vessel, and a probe for measurement and monitoring purposes. However, other devices are conceivable as well and should be within the scope of the person skilled in the art.

The conical contact will guarantee that no external loads or vibration passes through the seal, when the preload-path is confined within a very short circuit, between said contact and bolts. This access fitting will have a built in safety against blow-outs, by the device being held urged against the fitting with a high contact-pressure, creating a tight orifice even in case of a complete seal-failure.

Additionally, this invention will allow for a tertiary seal between threaded cover nut and fitting. Drawings

The invention will now be described in further detail by an example of an embodiment of the present invention by means of drawings, where equal numeral references have been used to identify similar or identical parts of the respective drawings, suffixed by a character were applicable:

Figure 1 illustrates a longitudinal cross-section of one example of a prior art access fitting for attaching a probe within a pipeline or vessel containing fluids;

Figure 2 illustrates a longitudinal cross-section of another example of a prior art access fitting for attaching a probe within a pipeline or vessel containing fluids; Figure 3 illustrates a longitudinal cross-section of one embodiment of an access fitting in accordance with the present invention for attaching a probe within a pipeline or vessel containing fluids; and

Figure 4 illustrates a partial cross-section of the primary seal the encircled area indicated by SD in figure 3.

Detailed description of the invention

Now referring to Fig. 1, the drawing illustrates a prior art access fitting for attaching a probe 6 within a fluid containing pipeline or vessel 7 in the form of a cross-section taken along the longitudinal axis of the probe 6 and its attachment device. A pipe or vessel fitting 2, hereinafter also referred to as "fitting", is sealed and preloaded in a conventional fashion by a threaded plug 1, matching an equally threaded fitting 2, which together preloads a conical annular seal 3, arranged in an annular groove provided in the plug 1, against said fitting's conical inside, all in order to seal off the probe 6 from the atmosphere. A cover 4 is attached at the rear end of the plug 1 for protection against the environment only.

Now referring to Fig. 2, the drawing illustrates a prior art access fitting for attaching a probe 6b in a manner similar to Fig. 1. A pipe fitting 2b is sealed off and preloaded in an alternative manner by a threaded cover 4b, matching an equally threaded fitting 2b, which together clamps the plug lb against said fitting and preloads the conical seal 3b against said fittings conical inside.

One embodiment of an access fitting for attaching a device, e.g. a probe, in accordance with the present invention is illustrated in Fig. 3, where a pipe fitting 2c is sealed off and preloaded. The plug lc is preloaded by externally threaded pins 5 accommodated within corresponding radially extending apertures 8 formed in the fitting 2c. A seal 5'is inserted into an annular groove 5" formed in the surface of the aperture 8. The plug Is is the region of the aperture 8 in the fitting 2c provided with a beveled surface lc'. This arrangement provides a conical metal-to-metal contact directly between the fitting 2c the pin 5 and plug lc. A radially compliant seal 3c becomes self- energized by the line-pressure in the pipe. The cover 4c is equipped with a seal 4c' arranged between the cover 4c and the rear end of the fitting 2c, to seal against the atmosphere together with the fitting 2c. The gap S indicates the clearance between the plug lc and the cover 4c after installation.

Figure 3 illustrates two threaded pins 5 arranged at an angle less than 90° with regard to the longitudinal axis of the plug lc and probe. The angle between the pins 5 and the longitudinal axis of the plug lc including the number of pins may vary. Accordingly, the number of pins could be three, four, five or even six. A person skilled in the art will be able to calculate the number of pins required in view of the present description and the pipeline pressure involved, pin dimensions, angle etc. The angle between the longitudinal axis of the pins 5 and the longitudinal axis of the plug lc and probe may also vary with the material chosen, dimensions and pressure involved. Accordingly, an exemplary angle between the longitudinal axis of the pins 5 and the longitudinal axis of the plug lc and probe could be 60°. However, the invention is not limited to any specific number of pins 5 in excess of 5 or any specific angle less than 90°.

The encircled area (circle included for illustration purposes only) in Fig. 3 is detailed in Fig. 4. The radially compliant seal 3c of Fig. 3 comprises an outer seal part 3c' of a substantially incompressible solid material, such as a hard polymer material, and an inner seal part 3c" of a substantially compressible or resilient material. The directions "inner" and "outer" is here meant to indicate the directions with regard to the outer surface of the plug lc. The seal 3c is arranged in an annular groove provided in the outer periphery of the plug lc. The seal parts 3c' and 3c" are in fluid communication with the internal part of the pipe or vessel (not illustrated in Fig. 4), so that the fluid pressure which act upon the seal parts 3c' and 3c" and thus urge the resilient seal part 3c" against the sealing surface 2c' of the probe. The presence of the substantially incompressible seal part 3c' will prevent the resilient seal part 3c" from being extruded by the fluid pressure and thus maintain its sealing effect. The person skilled in the art will readily be able to choose the applicable seal material with support in the present description. Examples of materials for use with the resilient seal art 3c" are: NB , FCM and EPDM. Similarly, examples of materials for the substantially incompressible seal part 3c' are PFTE based polymers and polymers reinforced by glass and/or carbon.

Whereas the description above has been directed to the constructional details of the present invention, the description below clarifies the surprising technical effect of the access fitting in accordance with the present invention.

As the access fitting according to the invention is assembled, the plurality of angularly mounted and threaded pins 5 are tightened with a pre-determined torque in order to preload the plug lc with an equally pre-determined force, against conical surface 2c' of the fitting to provide a metal- to metal contact. This conical contact will guarantee that no external loads or vibration passes through the seal, while the preload-path is confined within a very short circuit, between said contact and bolts, where the latter itself is beneficial in case of different thermal expansion between plug and fitting.

Said torque is designed to give said contact the proper level of preload, in order to overcome the expected counter-force from the line-pressure in to provide a certain margin against leakage.

The self energized primary seal 3c can have any numerous designs, as long as it is not dependant on a mechanical preload to serve its sealing functions. In case of a complete seal failure, the invention will still have a built in secondary seal against dramatic blow-outs, by the plug itself being held urged against the fitting's sealing surface 2c' with a high metal-to metal contact-pressure, creating a tight orifice which will hold its integrity even when subjected to the extreme temperatures from a petroleum-fueled fire.

The seal 4c' between cover 4c, and fitting 2c (Fig. 3), forms together with the threaded pin seals 5', a tertiary seal, which can be used for leakage detection by monitoring the pressure inside said cover, built up between secondary and tertiary seal.

The access fitting will also be fail-safe against human error if the pins 5 are unlocked by mistake during operation. The plug lc can only travel a certain distance "S" before it will be supported by the cover, thereby limiting the gap to the sealing surface 2c' and securing the seal's function.

Accordingly, the access fitting in accordance with the present invention provides a pipe or vessel fitting which increases sealing efficiency and safety, reduces torque needed for necessary preload and at the same time improves the plug's lateral stiffness.