METHOD AND DEVICE FOR DETECTING FAULTS IN NON-CONDUCTIVE COATINGS ON UNDER WATER PIPELINES

• US 3,753,091 A
• Filed: 04/10/1972
• Issued: 08/14/1973
• Est. Priority Date: 04/10/1972
• Status: Expired due to Term

• Current Assignee: Walter J. Daspit
• Original Assignee: Walter J. Daspit
• Inventors: Daspit, Walter J.
• Primary Examiner(s): Strecker, Gerard R.
• Application Number:
  US05/242,870
• Time in Patent Office: 491 Days
• Field of Search: 324/3,37,40,54,52,67 61/72.3,72.4,72.5
• US Class Current: 324/557
• CPC Class Codes: G01N 27/83 by investigating stray magnetic fields

Abstract

The method of and apparatus for detecting faults in nonconductive coatings on underwater pipelines as the pipes are being laid by lay barges unto the ocean bottom or after the pipes have been laid on the bottom. The detector of the apparatus comprises in lay barge and jet barge embodiments three electromagnetic pickup coils placed near the pipe surface which detect a change in an electromagnetic field produced by a fault in the non-conducting coating as a low voltage is applied across the pipe. A Wheatstone bridge hookup is provided to maximize the effects of the system. One of the three coils is used as the primary sensing coil while the other two are used to indicate when the electromagnetic field is being unbalanced by the presence of nearby metal objects rather than by a fault in the coating. A simplified hand-held model having one coil is likewise disclosed.

Claims

1. An off-shore apparatus for detecting faults in non-conductive coatings on underwater metal pipelines comprising:

signal producing means electrically connected to the pipeline for producing a signal in the pipeline;

signal detection means placed underwater in juxtaposition to the underwater pipeline for detecting signal changes which are a function of any substantial variation in the non-conductive characteristics of the coating on the coated pipeline, such as a fault in the coating;

support frame means, being at least in part underwater and straddling the underwater pipeline, for supporting and mounting said signal detection means in fixed relationship to the pipeline; and

movement means for moving the pipeline and said support frame means relative to each other so that the pipeline moves through said support frame means, said signal detection means being held by said support frame means only a relatively short but uniform distance from the pipeline;

whereby faults in the nonconductive coating on the pipeline can be detected underwater.

2. The apparatus of claim 1 wherein said signal producing and said signal detection means are electrical in nature, said signal producing means being electrical means for putting a voltage on the metal pipeline, producing an electromagnetic field surrounding the pipeline, and said signal detection means being electromagnetic sensing means for measuring the electromagnetic field produced by said signal producing means.

3. The apparatus of claim 2 wherein said electromagnetic sensing means comprises a set of at least three electromagnetic pickup coils, two of which are placed in a symetrically opposing position about the pipeline with respect to the third coil, one of said two coils being electrically connected in series with said third coil whereby the voltage induced in said coils by said electromagnetic field normally cancel each other out, the other coil being used as the primary sensor of the electromagnetic field and the two coils connected in series being used as a back-up, checking system.

4. The apparatus of claim 3 wherein said electrical means includes an impedance bridge network with the pipeline at one leg thereof;

whereby the impedance of the pipeline can be balanced in the system.

5. The apparatus of claim 3 wherein said electromagnetic sensing means includes at least one electromagnetic pickup coil completely surrounded and encapsulated in a dielectric medium having a substantial thickness;

whereby the electromagnetic field effect of inducing current in the coil is greatly enhanced.

6. The apparatus of claim 3 wherein said signal producing means is a low voltage.

7. The apparatus of claim 1 wherein the pipeline is being laid off a lay barge through a stinger, said support frame means being attachEd to the downstream end of the stringer, whereby any faults caused in the pipeline coating by the stinger can be detected.

8. The apparatus of claim 7 wherein said support frame means includes a yoke structure having two straddling, flanking sides upon which said signal detection means are mounted.

9. The apparatus of claim 8 wherein said yoke structure is four-cornered, the four corners being symmetrically disposed about the pipeline, said yoke including at each corner a set of roller bearing members which contact and mate with the pipeline as it moves past said support frame means, the roller bearing members serving to maintain said signal detection means in fixed, spaced relationship to the pipeline.

10. The apparatus of claim 9 wherein said support frame means includes an upper ballast tank, the lower two roller bearing members being movable laterally away from the pipeline, said support frame means being removable from the underwater pipeline to the surface by moving the lower two roller bearing members away from the pipeline and filling the ballast tank with air causing the support frame means to be freed from the pipeline and floated to the surface.

11. The apparatus of claim 1 wherein the pipeline is already on the water bottom and is being worked on at the bottom by a jet sled, said support frame means being attached to the back of the jet sled, whereby any faults caused in the pipeline coating by the jet sled can be detected.

12. The apparatus of claim 1 wherein there is further included in the apparatus fault recording means for recording the location on the pipeline of any detected fault.

13. The apparatus of claim 12 wherein said fault recording means is located on said support frame means.

14. The apparatus of claim 12 wherein said fault recording means includes means for recording the time of fault detection and means for measuring the rate and amount of a pipeline movement through said support frame means.