GB2325292A

GB2325292A - Hot water heat tracing pipe

Info

Publication number: GB2325292A
Application number: GB9709708A
Authority: GB
Inventors: Keith Shotbolt
Original assignee: Foster Wheeler Energy Ltd
Current assignee: Amec Foster Wheeler Energy Ltd
Priority date: 1997-05-13
Filing date: 1997-05-13
Publication date: 1998-11-18
Also published as: GB9709708D0

Abstract

The metal pipe 10, for joining end to end with similar pipes to create a pipeline, is surrounded by a sleeve of insulation 14 and one or more passages or conduits 16 extending longitudinally are provided such that the insulation defines the passage or conduits at least in part, the passages or conduits being in close proximity to the outer surface of the metal pipe and being arranged for the passage of heat tracing water.

Description

HOT WATER HEAT TRACING This invention relates to hot water heat tracing and, in particular, to pipes which are capable of being used for hot water heat tracing and to a method of using such pipes when assembled into pipelines.

Pipelines are designed to carry many materials and when the material is fluid, i.e. liquid or gaseous, at ambient temperatures, the pipeline need be little more than a metal pipe to act as a conduit with suitable corrosion coatings to avoid rusting or other degradation of the pipe itself. Some materials, however, can be very hot and may need to be kept at such high temperatures or at least their heat needs to be insulated from the surroundings of the pipeline. Under these circumstances, such pipelines will usually be provided with some form of insulating coating to prevent heat loss and to prevent contact with the very hot pipeline. Usually, insulating coatings of this type will then need an outer protective coating or sheath to avoid mechanical damage to the insulation.

Particular problems, however, exist when the contents of the pipeline are capable of solidifying at ambient temperatures. A typical example here is the transport of heavy oils which may solidify and become impossible to pump at ambient temperatures, and gases which contain water may form hydrates which can block a pipeline. In such a situation, good insulation of the pipeline can keep the flowing temperature warm, but this is not a solution in the event of a shutdown in the pipeline for some reason or another which can result in cooling to a low temperature and solidification of the pipe contents.

For this reason, heat tracing is used, that is to say, the application of heat to the pipeline in some manner so as to keep the contents of the pipeline at a desired temperature or remelt deposits and/or contents when necessary.

Hot water heat tracing has been used in circumstances such as the pumping of liquid sulphur where two coaxial tubes are used with the liquid sulphur passing through the central tube and heated water flowing through the outer tube in the space between the two tubes. The requirement for coaxial tubing, however, is a substantial additional complication. This may be acceptable for pipelines which are in a simple environment such as being buried in a trench in the ground. However, this complication would be particularly significant in pipelines which act as risers for conducting crude oil from a well head on the seabed up to the production vessel floating on the surface of the water.

An alternative procedure is electrical heat tracing where electrical heating or resistance wires are placed in contact with the pipeline and covered with some suitable insulation. By passing electric current through such wires localised heating can be provided to keep the pipeline hot and/or to melt deposits or the completely solidified contents of the pipeline. Electrical heating has not proved particularly satisfactory in this area since the electrical heating wires are not long lasting and their replacement is a significant complication and one which could not be accepted in a riser from a well head in relatively deep water.

It is, therefore, an object of the invention to provide simplified hot water heat tracing for pipelines.

According to the invention, there is provided a pipe for joining end to end with similar pipes to create a pipeline, the pipe comprising a central metal pipe, at least one sleeve of material surrounding the pipe, and one or more passages or conduits extending longitudinally of the pipe and in close proximity to the outer surface of the metal pipe for the passages of heat tracing water.

The sleeve may be of thermal insulation or thermal inertia material.

The passages or conduits may extend longitudinally through the material with the material defining, at least in part, the passages or conduits. Alternatively the passages or conduits may be provided at the edge of the inner cylindrical surface of the material such as the insulation, e.g. between the metal pipe and the insulation.

Also according to the invention, there is provided a method of hot water heat tracing for a pipeline in which a metal pipeline has at least one sleeve of surrounding material such as insulation one or more longitudinal water passages are provided in close proximity to the outer surface of the metal pipeline and hot water is passed through those passages in order to maintain the contents of the pipeline at or above a particular temperature and/or to melt deposits or solid material within the pipeline.

An advantage of the invention is that pipelines with a coating of insulation are well known and are widely used in, for example, oil exploration particularly where risers from a sea floor to a production vessel are required.

Therefore, no particular changes in such pipelines, other than the provision of water conduits, is required. Also, the technology exists for joining individual tubes of this nature into pipelines and again the only additional difference required, according to the invention, is the provision of continuity of the passages or conduits across the joins.

The pipes themselves are usually steel but in some cases may be titanium. When they are steel they will usually need an anti-corrosion layer adjacent to the outer surface of the metal pipe. Such anti-corrosion layers are well known and can be relatively thin and will readily transmit heat from the heat tracing water to the contents of the pipeline. In the case of titanium pipelines, however, this is not usually necessary since the titanium would not be corroded by contact with the hot heat tracing water.

Materials for insulating such pipelines are well known and are generally based on foamed plastics materials such as polyurethane and polypropylene. An example of a known thermal insulation layer and process for applying it to pipelines for use in oil production is that known as Thermotite (trade mark). This system uses a foamed polypropylene insulation and comprises polypropylene foam, polypropylene solid and polypropylene syntactic foam. The Thermotite process has been patented by Norsk Hydro and is available from companies such as Thermotite Limited in the United Kingdom.

Over the insulation layer one will usually require an outer shield or protective layer. This can be a sleeve applied in a conventional manner.

The water conduits themselves can be wholly within the insulation or can be provided at the inner surface of that insulation. Alternatively, the channels may be formed within the insulation. An alternative arrangement is to provide an annular space between the outer surface of the pipeline or corrosion coated pipeline and the inner surface of the insulation with a number of longitudinally extending spacers positioned within that annular space to provide discrete conduits between adjacent spacers for the passage of the water.

The number of conduits provided is not critical but preferably the conduits are relatively shallow in the radial sense and have a relatively large angular size so as to provide a substantial cross-section for ease of water flow yet they will not contribute to a substantial increase in overall diameter for the pipeline as compared with a conventionally insulated pipeline. According to one preferred embodiment there are an even number of such conduits and half of the conduits can then be used to conduct the hot water in one direction along the length of the pipe and other half used to return the water in the opposite direction. In this way one can make very effective and efficient use of the heat and need only have one heating station for the water. Desirably the outward and return conduits alternate around the pipeline.

The invention will now be described, by way of example, with reference to the accompanying drawing which is a cross-section through one form of pipe according to the invention.

Figure 1 shows one possible configuration for a hot water heat tracing pipe according to the invention. Here a central metal pipe 10 is provided with four spacers 12.

These are positioned at approximately 900 intervals and over the spacers is provided a sleeve of insulation 14. As a result water passages or conduits are defined between adjacent spacers.

Such a pipe can be provided with known corrosion layers on the outer surface of the metal pipe 10 and will normally be provided with suitable shield layers around the insulation. Such components are well known and for simplicity are not shown in the drawing.

Pipes can be joined end to end to form a pipeline in a largely conventional manner. It is just important to provide for continuity of the conduits 16 across the joins between adjacent pipes.

In an alternative embodiment conduits can be provided in the thermal inertia layer of a pipe of the type known as ThermoStore (trade mark) which is available from Balmoral Webco Pipeline Systems. This includes a metal pipe covered with an anti-corrosion layer. Over this is a thermal inertia layer in which the conduits are provided. This layer has a high heat capacity and so acts as a thermal reservoir which, together with the hot water heat tracing, can substantially increase the time for which a pipeline retains a temperature above which its contents will solidify. Over this thermal inertia layer is provided an optional sheath and this is covered with an insulation layer.

Claims

1. A pipe for joining end to end with similar pipes to create a pipeline, the pipe comprising a central metal pipe, at least one sleeve of material surrounding the pipe, and one or more passages or conduits extending longitudinally of the pipe and in close proximity to the outer surface of the metal pipe for the passage of heat tracing water.

2. A pipe as claimed in Claim 1 in which the passages or conduits are provided such that the said material of a sleeve surrounding the pipe defines the passages or conduits at least in part.

3. A pipe as claimed in Claim 2 in which the passages or conduits are wholly within the said material.

4. A pipe as claimed in Claim 2 in which an annulus is provided outside the pipe at the inner surface of the sleeve of the said material, and a number of spacers are positioned around that annulus to divide it into a number of passages or conduits.

5. A pipe as claimed in any proceeding claim in which the said material is insulating material to reduce heat losses from fluid passing along the pipe.

6. A pipe as claimed in any of claims 1 to 4 in which the said material is thermal inertia material.

7. A pipe substantially as herein described with reference to the accompanying drawing.

8. A method of hot water heat tracing for a pipeline in which a metal pipeline has at least one sleeve of surrounding material such as insulation one or more longitudinal water passages are provided in close proximity to the outer surface of the metal pipeline and hot water is passed through those passages in order to maintain the contents of the pipeline at or above a particular temperature and/or to melt deposits or solid material within the pipeline.