GB2180068A

GB2180068A - Probe for corrosion testing

Info

Publication number: GB2180068A
Application number: GB08522006A
Authority: GB
Inventors: Roe Strommen
Original assignee: Corrocean ASA
Current assignee: Roxar AS
Priority date: 1985-03-01
Filing date: 1985-09-04
Publication date: 1987-03-18
Also published as: GB8522006D0

Abstract

A probe for corrosion testing includes a spirally wound resistance element (13) on a rod shaped insulating member 12 which is reinforced by an electrically conductive rod member 11. The element is partially covered by a moulded portion 19 which therefore shields part of the element, the remainder of the element being exposed. The exposed end of the element 13 is connected to the rod at 14. The other end of the element 13 and the rod 11 are respectively connected to electrical conductors 16, 17. The central part of the element is connected to a further conductor. The conductors 16, 17 and 15 are used to connect the exposed and unexposed parts of the element 13 to a bridge network whereby the resistance of the exposed element part can be monitored. <IMAGE>

Description

SPECIFICATION Probe for corrosion testing This invention relates to a probe for the testing or monitoring ofthe effects of a corrosive environment involving providing a corrodable resistance element which is helically arranged on an electrically insulating support. The probe is intended to be permanently installed in the region at which the corrosive environmentoccurs. Such location can be inthewall of a pipe, tank or other structure in which corrosive conditions are likely to occur.

Probes for testing for corrosion are used in various forms of equipment, installations and structures, e.g., in systems, more particularly offshore systems, for processing petrochemical products. The active components of such probes are preferably prepared from an active metallic material that is similartothat used in the equipment etc., to be protected, e.g, the material of the tank or pipe wall. The probes are fitted with screw type threads so that they can be screw mounted to the location of use in such mannerthat the active part of the probe is in contact with the same medium asthe equipment itself i.e.,the medium being transported through the pipe or contained in the tank. In practice, the active part of the probe is connected to a remotely located electrical measurementcircuit.

Oneform of such measurement equipment in- volves resistance bridge network arrangements in which the electrical resistance ofthe exposed active metallic part of the probe which is exposed to the corrosive conditions is compared with the resistance of a similar non-active part of the probe which is not exposed to the corrosive conditions.

In use of such probes it is found that decrease in the area ofthe active element i.e., the corroded element causes the electrical resistance to increase and present a measure ofthe corrosion of the equipmentconcerned. Such probes are generallytermed "electrical resistance probes" or ER probes. Such ER probes may have an additional resistance element with the same properties as those ofthe active element, but sealed from the influence ofthe corrosive envoironment and thereby acting as a reference element, whereby during the balancing procedures of the bridge network a desirable temperarure com- pensation can be achieved.

British Patent No 1,402,413 discloses a probe having a helical conductive element arranged on an electrically non-conductive, rod shaped core. It has been found that this known construction exhibits certain shortcomings as a consequence of the nature ofthe core material together with the use of a separate electrical conductorforthe connectionsforeach end of the resistance element thereby complicating the mounting ofthe probe.

Furthermore, it has been found that the conductive element is liable to be attacked in particular bycorrosion occurring in the fissures created between the core and the conductive element which corrosion has been found to lead to erroneous measurements being made by the probe.

Figure2 is a section on the line ll-ll of Figure 1.

Referring now to the drawing a probe includes a cylindrical support rod 11 of steel or other electrically conductive material having corresponding physical properties. A sheathing 12 of a synthetic material which is preferably elastomeric and which is electric ally insulating encloses the main part ofthe rod 11 including one end thereof.

The insulating sheathing 12 which can have an cylindrical external surface so that the sheathing is effectively a hollow cylinder is such that the rod may be firmly embedded therein. The sheathing carries a helically or otherwise spirally wound or arranged strip 13 of a carbon steel orother metallic material depending uponthematerial ofthepipewall,tankor other structure at the location at which the corrosion is to be tested or otherwise monitored. The strip 13 has a pitch which is largerthan the width thereof thereby leaving the surface of the sheathing exposed along a helical space or passage lengthwise of the sheathing 12 which is electrically insulating.

The end ofthe strip 13 adjoining the closed end of the sheathing is electrically connected to the one end ofthe central rod 11 as is indicated at 14. The centre of the strip 13 is connected to an electrically insulated wire 15,whilethe other end ofthe strip 13, adjoining the other end ofthe rod 11 is connected to an electrically insulated wire 16. An electrically conductive wire 17 is connected to said other end of the rod.

It is a primary object of the present invention to provide an improved probe ofthe kind above discussed and to produce a probe which is particularly suitable for mounting in the wall of a pipe ortankand which makes use of comparative electrical measurements whereby the changes in ambient conditions such as temperature may be compensated.

According to the present invention there is provided a probefortesting corrosion, including an electrical resistance element of a corrodable material, the resistance element being spirally arranged upon the surface of an electrically insulating support member, an electrically conductive reinforcement memberfor internally reinforcing the support member, means for enclosing orshrouding a portion ofthe length of the support member and thus a corresponding portion of the length ofthe resistance element including one end thereof thereby effectively to separate the resistance element into an unexposed portion including the element one end and an exposed portion including the other end of the element, an electrical connection between said other end of the resistance element and the reinforcement member, and means for enabling connection of a measuring circuittothe reinforcement member, and said one end ofthe resistance element.

For a better understanding of the invention and to show how to carry the same into effect reference will now be made to the accompanying drawing in which: Figure lisa side view ofan embodimentofa probe incorporating the features of the invention; and The electrically insulating space or passage defined between the adjacent turns of the strip 13 is filled-in or otherwise covered by an electrically in sulating material 18, such that the outer surface of the material 18 is flush or level with the spiral outer surface of the strip 13, whereby the outer surface of the probe presents an initially uniform diameter.

The portion ofthe strip located between said one end and the location ofthe connection of the wire 15 with the strip 13 is enclosed by a housing 19 which effectively shrouds or encloses the surface of this portion of the strip 13. The housing 19 is preferably moulded such asto ensurethata sealed bond is made with the carrying structure 13, 18. In a modified embodiment, the strip 13 is provided with its carrying and covering parts by a moulding process. With this embodiment the necessary electrical connections are prepared priorto the moulding process.

The housing 19 is provided partly to shroud a portion ofthe strip 13, and partly to facilitate the mounting ofthe probe in a wall, e.g., a pipe ortank. Forthis pupose the housing 19 can be provided with threads (notshown) or otherwise made suitableformounting in an opening, such as a bore ora bushing.

The wires 15,15 and 17 are connected to a resistance bridge type of measuring circuit (not shown) in such manner as to enable the use of the exposed and nonexposed portions of the strip 13 as the unknown and reference resistances of a measuring bridge.

Thus the exposed outer part of the strip 1 3forms the unknown resistance whilst the covered partwill provide the reference element of the bridge.

Itwill be appreciatedthatthe rod 11, in addition to functioning as an electrical conductor acts as a reinforcementforthe probe.

The diameter of the active part of the probe shown may be 1 0-30mm and the length ofthe protruding, active part 10-100mm.The required suitable physical properties ofthe materials in any particilar aplication may be readilly determined of a person skilled in the art. Furthermore, the srrip 13 is preferably prepared from a material with resistance to corrosion corresponding to that of the structure to be tested.

The length of the strip 13 may be 400mm, its width 3mm and its depth 1 mm.

The probe may be modified, e.g., in regard ofthe method of manufacturing, its dimensions, it shape of section, and the selection ofthe materials. Such modifications are considered to be within the scope ofthe invention as defined in the accompanying

Claims

claims. CLAIMS

1. A probefortesting corrosion, including an electrical resistance element of a corrodable material, the resistance element being spirally arranged upon the surface of an electrically insulating support member, an electrically conductive reinforcement memberfor internally reinforcing the supprot member, meansforenclosing orshrouding a portion ofthe length of the support member and thus a corresponding portion of the length ofthe resistance element including one end thereofthereby effectively to separate the resistance element into an unexposed portion including the element one end and an exposed portion including the other end of the element, an electrical connection between said other end of the resistance element and the reinforcement member, and means for enabling connection of a measuring circuit to the reinforcement member, and said one end of the resistance element.

2. A probe as claimed in claim 1 ,wherein there- sistive length of the enclosed part and that of the exposed portions ofthe element are equal.

3. Aprobeasclaimed in claim 1 or2,whereinan electrically insulating mateterial is provided between adjacentturns of the resistance element, the arrange- ment being such that the surface ofthe exposed portion of the resistance element is flush with the sur- face ofthe insulating material.

4. A probe as claimed in claim 1,2 or 3, wherein the support and the covering means are moulded from a synthethic elastomeric material as an integral element.

5. A probe as claimed in claim 1,2,3 or 4, wherein the covering means is adapted for mounting the probe inthewall of a vessel or pipe orthe like ata location where the corrosion isto be tested in such mannerthatthe exposed portion ofthe resistance element projects into the corrosive environment.

6. A probe for testing corrosion constructed and arranged to operate substantially as herein before described with reference to the accompanying drawings.