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Zawartość zarchiwizowana w dniu 2022-12-27

FIELD IMPLEMENTATION OF A NOVEL TECHNIQUE FOR DETECTION OF CORROSION UNDER INSULATION IN OIL AND GAS PROCESS PIPEWORK

Cel

This project addresses the need to monitor long lengths of insulated pipe in complex pipework systems for oil and gas production and processing in order to detect corrosion under the insulation. Such localised corrosion can cause premature and unexpected failure which may result in potentially catastrophic releases of hydrocarbons into the environment. A novel low frequency, long range ultrasonic technique allows long lengths of pipe to be examined without the need to remove large areas of insulation. The aim of the project is to produce a test system suitable for field use, which is capable of detecting and locating corrosion of 30-50% wall loss over a 3t x 3t area (where t is the wall thickness) in lagged piping in the diameter range 50 to 300mm (2 to 12 inches), with a false call rate of 10% or less and a usable test range of at least l5m.
The results to date show that :
* The technique is capable of detection of both pipework features and corrosion under plant conditions.
* To obtain optimum test conditions, careful control over both the set up and input is needed. Procedures exist to achieve this.
* Well defined procedures are necessary for analysis of the output from the test system. These are currently being developed and will be used in a forthcoming series of site trials
* A mechanised device is necessary for efficient attachment of the transducer arrays on to pipes to be tested.
The key features of this technique are the use of ultrasonic waves at the low frequency end of the ultrasonic range (50-5OOkHz) and the introduction of selected guided wave modes which are transmitted along the pipe wall. These waves can propagate large distances (hundreds of metres) in continuous welded pipe runs and are largely unaffected by the presence of external lagging. However, if the correct wave modes are generated, they are sensitive to thickness changes which allows localised corrosion to be detected. Important technical elements are the means of generating the correct wave modes and the means of analysing received signals after propagation along the test piece, in order to discriminate between corroded and uncorroded pipes.
There is currently no satisfactory non-destructive test method for detection of corrosion under insulation. Thus, the majority of pipework on oil and gas production and processing installations is not subjected to any in-service monitoring, such that its condition and therefore its integrity are uncertain. Of the approaches which have been attempted for examination of insulated pipework, profile radiography is very slow as only a small area of pipe can be examined in each test, requiring 100% coverage of the test piece with the test apparatus, and there are hazards of exposure to ionising radiation. Low frequency eddy current techniques again require a sensor to be scanned over the entire surface to be examined and are defeated by external metallic cladding surrounding the insulation or by wire mesh, which is widely used to hold the insulating material in place. The availability of the long range ultrasonic inspection technique will provide a unique global means of assessing piping condition and is therefore expected to capture a major share of the market for inspection of pipework in oil and gas installations.
At the end of 1992 EC oil production was 2.3 million barrels per day, 80% from UK offshore wells. All topside separation and processing installations require inspection for corrosion in pipework. A typical annual inspection budget for topside plant is around UKL 300,000 of which approximately 1/3 is spent on monitoring for corrosion. The poor access for inspection in topside plant makes long range monitoring particularly attractive. The current emphasis on de-manning of offshore installations and on extending the operating life of such plants will increase the need for monitoring techniques of this nature. In addition, there are 39 onshore gas processing plants and 100 oil refineries in the EC, for which corrosion under insulation is a significant problem owing to the temperature ranges in which such plants operate. The typical cost of on-stream monitoring of these types of plant for degradation, such as corrosion under insulation, is around UKL 200,000 per annum per plant. The market for testing in the UK offshore zone alone is estimated at UKL 5M per annum.

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Koordynator

Welding Institute
Wkład UE
Brak danych
Adres
Abington Hall Abington
CB1 6AL Cambridge
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