GB2213276A

GB2213276A - Simulating conditions encountered in welding an underwater pipeline in which fluid is flowing

Info

Publication number: GB2213276A
Application number: GB8829428A
Authority: GB
Inventors: Jean-Claude Ancenys; Jacques Farenc
Original assignee: COMEX
Current assignee: COMEX
Priority date: 1987-12-18
Filing date: 1988-12-15
Publication date: 1989-08-09
Anticipated expiration: 2008-12-15
Also published as: NO885573D0; DK698588D0; NL193348C; DK174388B1; NL8803008A; FR2625012B1; NO885573L; NO174078C; NO174078B; DK698588A; GB2213276B; FR2625012A1; NL193348B; GB8829428D0

Abstract

A method and apparatus for reproducing the conditions required for performing a welding operation on an underwater pipeline which is in service with a fluid flowing therealong wherein a test rig (1) is disposed inside a hyperbaric chamber (2), the rig comprising two coaxial pipelines (16, 17) delimiting an annular space (18) in which a helical wall 19 is wound at a constant pitch, and a turbulent flow of a fluid is established in the space (18) with the temperature, the pressure, and the flow rate of the fluid being selected to obtain a transfer of heat through the outer wall (16) which has the same characteristics as the underwater pipeline which is comparable to the heat transfer which would be obtained due to the flow of the said fluid in the said underwater pipeline which is in service. <IMAGE>

Description

A METHOD AND APPARATUS FOR REPRODUCING THE COSITIONS R-QU' ED FOR PERFORMING A WELDING OPERATION ON AN UNDERWATER PIP-LI,:n WHICH IS IN SERVICE WITH A FLUID FLOWING THEREALONG The present invention relates to a method and apparatus for reproducing the conditions required for performing a welding operation on an underwater pipeline which is in service with a fluid flowing therealong.

The technical field of the invention is that of equipment applicable to performing off-shore underwater work.

At present, in order to reproduce the conditions required for performing a welding operation on a pipeline in which a fluid is flowing, a test rig is set up which is constituted by a tube including a length having the same characteristics as the said pipeline, a loop is established on the test rig, and the same fluid is caused to flow round the loop as flows along the pipeline which is in service, e.g. oil or gas, after which the heat transfer conditions through the wall of the pipeline in service and in which said fluid is flowing are obtained, under atmospheric air.

Such pipelines may be large in diameter, e.g. about 1 meter, and it will readily be understood that such a test rig is expensive to set up and is relatively bulky and, for example, therefore cannot be used in a conventional hyperbaric chamber in order to reproduce the conditions of the welding to be performed on an underwater pipeline which is in service.

The present invention seeks to mitigate these drawbacks.

The present invention provides a method of reproducing the conditions required for performing a welding operation on an underwater pipeline in service in which a fluid is flowing, the method comprising the following operations: a first length of pipeline having the same characteristics as the pipeline in service is disposed in a hyperbaric chamber; a second length of pipeline having the same length as the first length and having an outside diameter which is smaller than the inside diameter of the first length is placed inside the first length of pipeline so that the first and second lengths of pipeline are coaxial and delimit an annular space therebetween; means are disposed in the annular space for generating a turbulent. flow of a fluid; the two ends of the annular space are closed;; a fluid is admitted under pressure via an inlet orifice situated at one end of the annular space and a flow of the fluid in the turbulent state is established in the annular space; the flowing fluid is returned via an outlet orifice situated at the other end of the annular space and the fluid is recycled; and conditions such as the distance between the walls of the two lengths of pipeline, the means for generating a turbulent flow of fluid, the temperature, the pressure, and the flow rate of the fluid, are selected so as to obtain heat transfer through the wall of the first length of pipeline comparable to the heat transfer obtained by the flow of the said fluid in the said underwater pipeline which is in service.

In the method, the following formula may be applied: P = H.(temperature of the ducting - temperature of the fluid), where P is the heat power and H is a transfer coefficient, the formula being applied as follows: P = H' . (temperature of the test length - temperature of the fluid flowing in the rig), and with average speed of the fluid flowing through the test rig being deduced from the characteristics and the temperature of the fluid, wherein the means for generating a turbulent flow are constituted by a helical wall, and wherein said deduced speed and the flow rate of the test rig fluid are used to define a flow cross-section in the test rig, i.e. the annular space between the two lengths of pipeline constituting the rig, and the pitch of the helical wall, such that a turbulent flow of fluid is obtained.

The invention also provides apparatus for reproducing the conditions required for performing a welding operation on an underwater pipeline in service in which a fluid is flowing, the apparatus comprising, in combination: a hyperbaric chamber which receives a test rig constituted by: a first length of pipeline having the same characteristics as the pipeline in service; a second length of pipeline having the same length as the first length of pipeline, which second length of pipeline has an outside diameter which is less than the inside diameter of the first length, the first and second lengths of pipeline being coaxial and delimiting an annular space therebet.een; means for generating a turbulent flow of a fluid situated in the annular space, the space including closure walls at its ends;; an inlet orifice for a fluid under pressure situated at one end of the annular space and an outlet orifice situated at its other end; and means for causing the fluid to flow in the annular space, and for adapting and monitoring its flow rate, its tmperature, and its pressure in such a manner as to obtain heat transfer through the wall of the first length of pipeline comparable to the heat transfer obtained by virtue of the flow of the said fluid in the said underwater pipeline which is in service.

In one embodiment, the means for generating a turbulent flow of fluid under pressure are constituted by a helical wall extending at a constant pitch over the length of the annular space, which wall engages in sealed manner both the inside face of the first length of pipeline and the outside face of the second length. The helical wall is constituted by a metal flat wound helically around the second length of pipeline and fixed thereto, with the metal flat together with the inside face of the first length delimiting a space which is filled by a sealing gasket.

The gasket is constituted by a bead put into contact with the inside face of the first length of pipeline and by two lips placed astride the metal flat, with the gasket being fixed to the metal flat by glue, and being made of high temperature silicone.

The inlet orifice for fluid under pressure is fixed to the wall of the second length of pipeline and the outlet orifice for the fluid is fixed to the wall of the first length.

The apparatus may also include: a tank containing the fluid; a fluid "go" circuit running from the tank, which circuit includes a pump for circulating and pressurizing the fluid from the tank, a flowmeter, a thermometer, and a pressure gauge, the circuit terminating at a sealed feed through going through the wall of the hyperbaric chamber, and a tube extending from the feedthrough to the inlet orifice of the second length of pipeline; and a "return" circuit running back to the tank comprising a tube running from the outlet orifice fixed to the first length of pipeline to a feedthrough going through the wall of the hyperbaric chamber, with the circuit including after the feedthrough, a thermometer, and a valve for adjusting and stopping the stream of fluid returning to the tank. The helical wall is orthogonal to the lengths of pipeline.

The invention can be used to reproduce underwater welding conditions on land in order to determine optimum conditions for performing a welding operation on an underwater pipeline which is in service and in which a fluid is flowing.

The advantages of the invention lie firstly with the operating conditions of the test rig in a hyperbaric chamber, with testing being performed at the sea bed pressure applicable to the in-service underwater pipeline on which welding operations are to be performed, secondly with the cost of the installation which cost is considerably smaller than that of test rigs currently being used, and thirdly with the ease with which the method can be implemented using equipment which is very simple.

An implementation of the invention is described by way of example with reference to the accompanying drawings, in which: Figure 1 is a diagrammatic cross-section through a hyperbaric chamber in which a test rig in accordance with the invention is disposed, the figure showing the devices for regulating the rig which are shown in diagrammatic form outside the hyperbaric chamber; Figure 2 is a longitudinal section view of a test rig similar to that of Figure 1; Figure 3 is a section view on line III-III of Figure 2; and Figure 4 is a fragmentary section view on a larger scale showing the implementation of the helical wall which extends within the annular space between the two lengths of coaxial pipeline.

In order to reproduce those conditions of an underwater pipeline in service which are determining for a welding operation, i.e. its internal pressure and its flow of gas or oil, a flow of fluid, e.g. water, is set up according to the invention between a first length of pipeline under test and a second length of pipeline which is coaxial with the first length, and with the second length having a helical wall welded thereto. The space between the two lengths of pipeline, the pitch of the helical wall, the temperature, the pressure, and the water flow rate are all selected so as to establish a turbulent flow ensuring that heat is transferred through the wall of the first length of pipeline in a manner which is comparable to the heat transfer obtained due to the flow of gas or oil in the underwater pipeline in service.

Said first'length of pipeline which constitutes the outer skin of the test rig is constituted by a length having characteristics which are similar or identical to those of the underwater pipeline in service (inside diameter, wall thickness, and grade of steel).

The length of the rig is naturally dictated by the maximum size that can be admitted into the hyperbaric chamber in which the tests are performed. The outside diameter of the second length of pipeline disposed coaxially inside the first length, and the pitch of the helical wall which winds over the length of the rig around second length of pipeline are defined as follows: the characteristics, in operation, of the ducting conveying the fluid make it possible to calculate the heating power which is required to reach the wall temperature needed to perform the welding operation.

The following equation is applied: P = H. (temperature of the ducting - temperature of the fluid) in which P is the heat power and H is a transfer coefficient.

By way of example, the following transfer coefficient has been used during testing:

= = thermal conductance D = (4S/p) hydraulic diameter o = density V = speed u = dynamic viscosity Cp = specific heat By using the same heating power on the test rig as on the pipeline in service, the object is to obtain the same temperatures in the welding zone.

To do this, the heat flux dissipated through the wall of the pipeline in service is written as being equal to the heat flux dissipated through the wall of the first length which constitutes the outer skin of the test rig: P = H'. (temperature of test length - temperature of water3.

The characteristics of the water and its temperature can be used to deduce the average speed of the water.

Given this speed, a flow cross-section (i.e. the annular space between the two lengths of pipeline constituting the test rig and the pitch of the helical wall) is defined in order to obtain a turbulent flow of water at a rate of about 8 m3/s.

It is verified that this flow cross-section allows a uniform flow to take place.

Naturally, the thicknesses of the two end plates and of the inner second length of pipeline are defined so as to withstand the internal pressure in the rig, which pressure may be necessary to prevent the water boiling.

An embodiment of apparatus in accordance with the invention for implementing the method is shown diagrammatically in Figure 1 of the drawings.

The test rig 1, which is described below, is placed inside a hyperbaric chamber 2 in which the pressure is identical to the sea bed pressure applied to the pipeline in service.

In order to perform testing, the water is caused to circulate by means of the following circuit: water is pumped from a basin or tank 3 by a pump 4 inserted in a tube 5 in which the following are also placed: a flowmeter 6, a thermometer 7, and a pressure gauge 8. The tube 5 ends at a feedthrough 9 into the hyperbaric chamber 2. The water goes from the feedthrough 9 to the inlet orifice of the rig by means of a tube 10 which may be flexible, for example.

After the water has flowed turbulently along the rig 1, it is recycled into the circuit. Another flexible tube 11 is fixed to the outlet orifice from the rig and extends to a second feedthrough 12 of the chamber 2. A tube 13 conveys the water back to the tank 3 and this tube includes a thermometer 14 and a valve 15 for adjusting and stop purposes.

Figures 2 to 4 show, in greater detail, the construction of a test rig 1 for implementing the method of the invention.

As shown in Figures 2 and 3, the test rig comprises a first length of 'pipeline 16 having the same characteristics as the underwater pipeline in service. A second length of pipeline 15 is placed inside the first length and coaxially therewith. As can be seen in the drawings, the second length has an outside diameter which is clearly smaller than the inside diameter of the first length 16, thereby leaving an annular space 18 between the two lengths 16 and 17.

A wall 19 is wound helically inside the annular space over the entire length of the rig, with the space between the two lengths 16 and 17, and the pitch of the helix 19 being defined as explained above.

The wall 19 (Figure 4) is constituted by a metal flat 19a extending orthogonally to the length of central pipeline 17 and to the outer skin 16. In order to facilitate fabrication of the rig, the metal flat 19a is not as tall as the space 18 between the two lengths 16 and 17. The helical wall 19 is sealed by means of a gasket 19b which is constituted by a bead 19bl bearing against the inside face 16a of the wall of the first length of pipeline 16 and mounted astride the metal flat 19a. The gasket 19b thus includes t.ó lips 19b2 and 19b3 extending substantially parallel to each other over the same length, and the gasket is fixed to the metal flat by means of glue. The gasket is preferably selected from the family of gaskets made of high temperature silicone.

The annular space 18 is closed at both ends of the rig by walls 20 and 21 which are welded to the lengths of pipeline 16 and 17 with the walls projecting beyond the lengths and being square in outline. Their central portions are open with the central portions extending to the inside periphery of the inner length of pipeline 17 in order to provide access to the inside thereof.

The rig also includes a water inlet orifice 22 fixed to the second length of pipeline 17 and an outlet orifice 23 fixed to the first length of pipeline 16. These orifices are made in centrally-tapped thickenings in order to enable the tubes 10 and 11 of the hydraulic circuit to be connected thereto.

Unlike the rig illustrated in Figure 1, the rig of Figures 2 and 3 includes a branch connection 24 constituted by a skirt welded to the middle portion of the length 16 during welding tests on the rig.

Naturally, the parts described above by way of example may be replaced by the person skilled in the art by equivalent parts performing the same function and without going beyond the scope of the invention.

Claims

1/ A method of reproducing the conditions required for performing a welding operation on an underazate- pipeline in service in which a fluid is flowing, the method comprising the following operations: a first length of pipeline having the same characteristics as the pipeline in service is disposed in a hyperbaric chamber; a second length of pipeline having the same length as the first length and having an outside diameter which is smaller than the inside diameter of the first length is placed inside the first length of pipeline so that the first and second lengths of pipeline are coaxial and delimit an annular space therebetween; means are disposed in the annular space for generating a turbulent flow of a fluid; the two ends of the annular space are closed;; a fluid is admitted under pressure via an inlet orifice situated at one end of the annular space and a flow of the fluid in the turbulent state is established in the annular space; the flowing fluid is returned via an outlet orifice situated at the'other end of the annular space and the fluid is recycled; and conditions such as the distance between the walls of the two lengths of pipeline, the means for generating a turbulent flow of fluid, the temperature, the pressure, and the flow rate of the fluid, are selected so as to obtain heat transfer through the wall of the first length of pipeline comparable to the heat transfer obtained by the flow of the said fluid in the said underwater pipeline which is in service.

2/ A method according to claim 1, in which the following formula is applied: P = H.(temperature of the ducting temperature of the fluid), where P is the heat power and H is a transfer coefficient, the formula being applied as follows: P = H' . (temperature of the test length - temperature of the fluid flowing in the rig), and with average speed of the fluid flowing through the test rig being deduced from the characteristics and the temperature of the fluid, wherein the means for seneratir. a turbulent flow are constitute by a helical wall, and wherein the deduced speed and the flow rate of the test rig fluid are used to define a flow cross-section in the test rig, i.e. the annular space between the two lengths of pipeline constituting the rig, and the pitch of the helical wall, such that a turbulent flow of fluid is obtained.

3/ A method of reproducing the conditions required for performing a welding operation on an underwater pipeline in service in which a fluid is flowing, the method being substantially as herein described with reference to the accompanying drawings.

4/ Apparatus for reproducing the conditions required for performing a welding operation on an underwater pipeline in service in which a fluid is flowing, the apparatus comprising, in combination: a hyperbaric chamber which receives a test rig constituted by: a first length of pipeline having the same characteristics as the pipeline in service; a second length of pipeline having the same length as the first length of pipeline, which second length of pipeline has an outside diameter which is less than the inside diameter of the first length, the first and second lengths of pipeline being coaxial and delimiting an annular space therebetween; means for generating a turbulent flow of a fluid situated in the annular space, the space including closure walls at its ends;; an inlet orifice for a fluid under pressure situated at one end of the annular space and an outlet orifice situated at its other end; and means for causing the fluid to flow in the annular space, and for adapting and monitoring its flow rate, its tem,perature, and its pressure in such a manner as to obtain heat transfer through the wall of the first length of pipeline comparable to the heat transfer obtained by virtue of the flow of the said fluid in the said undera.ater pipeline which is in service.

5/ Apparatus according to claim 4, wherein the means for generating a turbulent flow of fluid under pressure are constituted by a helical wall extending at a constant pitch over the length of the annular space, which wall engages in sealed manner both the inside face of the first length of pipeline and the outside face of the second length.

6/ Apparatus according to claim 5, wherein the helical wall is constituted by a metal flat wound helically around the second length of pipeline and fixed thereto, with the metal flat together with the inside face of the first length delimiting a space which is filled by a sealing gasket.

7/ Apparatus according to claim 6, wherein the gasket is constituted by a bead put into contact with the inside face of the first length of pipeline and by two lips placed astride the metal flat, with the gasket being fixed to the metal flat by glue.

8/ Apparatus according to claim 6 or 7, wherein the gasket is made of high temperature silicone.

9/ Apparatus according to claim 4, wherein the inlet orifice for fluid under pressure is fixed to the wall of the second length of pipeline and the outlet orifice for the fluid is fixed to the wall of the first length.

10/ Apparatus according to any one of claims 4 to 9, including a tank containing the fluid; a fluid "go" circuit running from the tank, which circuit includes a pump for circulating and pressurizing the fluid from the tank, a flowmeter, a thermometer, and a pressure gauge, the circuit terminating at a sealed feedthrough going through the wall of the hyperbaric chamber, and a tube extending from the feedthrough to the inlet orifice of the second length of pipelir.e;; and a "return" circuit running back to the tank comprising a tube running from the outlet orifice fixed to the first length of pipeline to 2 feedthrough going through the wall of the hyperbaric chamber, with the circuit including after the feedthrough, a thermometer, and a valve for adjusting and stopping the stream of fluid returning to the tank.

11/ Apparatus according to claim 5 or 6, wherein the helical wall is orthogonal to the lengths of pipeline.

12/ Apparatus for reproducing the conditions required for perfcrr.ing a welding operation on an underwater pipeline in service in which a fluid Is flowing, the apparatus benny substantially as herein described with reference to and as illustrated in the accompanying drawings.