GB2173310A - Testing of underwater structures by their vibration characteristic - Google Patents

Testing of underwater structures by their vibration characteristic Download PDF

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Publication number
GB2173310A
GB2173310A GB08508698A GB8508698A GB2173310A GB 2173310 A GB2173310 A GB 2173310A GB 08508698 A GB08508698 A GB 08508698A GB 8508698 A GB8508698 A GB 8508698A GB 2173310 A GB2173310 A GB 2173310A
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United Kingdom
Prior art keywords
structures
jig
testing
under test
sensor
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
GB08508698A
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GB8508698D0 (en
Inventor
Chengi Kuo
Gordon Hayward
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University of Strathclyde
Original Assignee
University of Strathclyde
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by University of Strathclyde filed Critical University of Strathclyde
Priority to GB08508698A priority Critical patent/GB2173310A/en
Publication of GB8508698D0 publication Critical patent/GB8508698D0/en
Publication of GB2173310A publication Critical patent/GB2173310A/en
Withdrawn legal-status Critical Current

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Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N29/00—Investigating or analysing materials by the use of ultrasonic, sonic or infrasonic waves; Visualisation of the interior of objects by transmitting ultrasonic or sonic waves through the object
    • G01N29/04—Analysing solids
    • G01N29/045—Analysing solids by imparting shocks to the workpiece and detecting the vibrations or the acoustic waves caused by the shocks
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01M—TESTING STATIC OR DYNAMIC BALANCE OF MACHINES OR STRUCTURES; TESTING OF STRUCTURES OR APPARATUS, NOT OTHERWISE PROVIDED FOR
    • G01M7/00—Vibration-testing of structures; Shock-testing of structures
    • G01M7/08—Shock-testing

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Acoustics & Sound (AREA)
  • Health & Medical Sciences (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Chemical & Material Sciences (AREA)
  • Analytical Chemistry (AREA)
  • Biochemistry (AREA)
  • General Health & Medical Sciences (AREA)
  • Immunology (AREA)
  • Pathology (AREA)
  • Investigating Or Analyzing Materials By The Use Of Ultrasonic Waves (AREA)

Abstract

Testing of underwater structures uses a test jig which is clamped to the structure and mechanically impacting the surface of the structure by a hammer device mounted on the jig. The resultant vibration signal is sensed by a sensor mounted on the jig. Instrumentation connected to the sensor and preprogrammed with data determine on a comparative basis whether the structure is air or water filled or cracked.

Description

SPECIFICATION Testing of underwater structures This invention relates to testing of under water structures.
Testing of under water structures such as may form part of an offshore oil or gas rig requires to be undertaken on a routine basis for the purposes of crack detection. Landbased inspection techniques have been utilised for this purpose but have been found to have poor reliability. Recently an ultrasonic technique has been developed for indirectly detecting cracks in tubular structures by determining whether or not the structure under test is flooded with water, this being on the basis that the jacket structures of rigs invariably consist initially of separate sealed compartments containing air at atmospheric pressure so that internal flooding indicates a throughwall defect somewhere on the structural member under test.The known ultrasonic technique is however dependent on manipulative control by a diver in order to align the ultrasonic transducer precisely normally to the wall of the structure under test, is dependent upon the structure under test being free of marine growth, and is limited in its application to tubular structures.
It is an object of the present invention to provide an improved method and apparatus for testing of under water structures.
According to the present invention a remotely controlled vehicle is provided with an arm fitted with clamp means for clamping the arm to a structure to be tested, and a test jig comprising hammer means and a vibration sensor, the vehicle including means for driving said hammer means to effect a mechanical impact on the structure to be tested and instrumentation means connected to the vibration sensor for monitoring the vibration signal detected thereby.
It will be appreciated that the impact on the structure created by the hammer means induces vibration of a resonant nature in the structure and which has a characteristic frequency spectrum dependent upon parameters including: wall thickness; structure dimensions; structure loading; external background noise; and material filling the structure. Consequently for any given structure wall thickness structural dimensions and loading are known so that the material filling the structure (i.e. air or water) can be determined from the signal detected by the vibration sensor. Of course the present invention is also applicable to nontubular structures.
Conveniently the instrumentation means is pre-programmed with data denoting the frequency spectrum of a structure to be tested when that structure is air filled or known to be crack free and the instrumentation means effects a determination of whether or not the structure under test is air or water filled or cracked on a comparative basis.
The present invention also provides a method of testing under water structures comprising clamping a test jig to the structure, mechanically impacting the surface of the structure by hammer means mounted in the jig, sensing the vibration signal generated by means of a sensor mounted in the jig, and comparing characteristics of that signal with characteristics of a predetermined vibration signal.
With the method and apparatus of the present invention there is no requirement for manipulative control of the test jig with any great precision but it is preferred that the hammer means and the sensor are relatively close together and that at least the sensor is capable of being held against the structure under test either resiliently by springs or hydraulically and it is for this latter reason that the clamp means are provided.
1. Apparatus for testing of underwater structures, said apparatus comprising a remotely controlled vehicle provided with an arm fitted with clamp means for clamping the arm to a structure to be tested, and a test jig comprising hammer means and a vibration sensor, the vehicle including means for driving said hammer means to effect a mechanical impact on the structure to be tested, and instrumentation means connected to the vibration sensor for monitoring the vibration signal detected thereby.
2. Apparatus as claimed in claim 1, wherein the instrumentation means is pre-pro gramme with data denoting the frequency spectrum of the structure to be tested when that structure is air filled or known to be crack free and the instrumentation means effects a determination on a comparative basis of whether or not the structure under test is air or water filled or cracked.
3. Apparatus as claimed in either preceding claim, wherein the vibration sensor is capable of being held against the structure under test either resiliently by springs or hydraulically.
4. A method of testing underwater structures comprises clamping a test jig to the structure, mechanically impacting the surface of the structure by hammer means mounted in the jig, sensing the vibration signal generated by means of a sensor mounted in the jig, and comparing characteristics of that signal with characteristics of a predetermined vibration signal.
**WARNING** end of DESC field may overlap start of CLMS **.

Claims (4)

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Testing of underwater structures This invention relates to testing of under water structures. Testing of under water structures such as may form part of an offshore oil or gas rig requires to be undertaken on a routine basis for the purposes of crack detection. Landbased inspection techniques have been utilised for this purpose but have been found to have poor reliability. Recently an ultrasonic technique has been developed for indirectly detecting cracks in tubular structures by determining whether or not the structure under test is flooded with water, this being on the basis that the jacket structures of rigs invariably consist initially of separate sealed compartments containing air at atmospheric pressure so that internal flooding indicates a throughwall defect somewhere on the structural member under test.The known ultrasonic technique is however dependent on manipulative control by a diver in order to align the ultrasonic transducer precisely normally to the wall of the structure under test, is dependent upon the structure under test being free of marine growth, and is limited in its application to tubular structures. It is an object of the present invention to provide an improved method and apparatus for testing of under water structures. According to the present invention a remotely controlled vehicle is provided with an arm fitted with clamp means for clamping the arm to a structure to be tested, and a test jig comprising hammer means and a vibration sensor, the vehicle including means for driving said hammer means to effect a mechanical impact on the structure to be tested and instrumentation means connected to the vibration sensor for monitoring the vibration signal detected thereby. It will be appreciated that the impact on the structure created by the hammer means induces vibration of a resonant nature in the structure and which has a characteristic frequency spectrum dependent upon parameters including: wall thickness; structure dimensions; structure loading; external background noise; and material filling the structure. Consequently for any given structure wall thickness structural dimensions and loading are known so that the material filling the structure (i.e. air or water) can be determined from the signal detected by the vibration sensor. Of course the present invention is also applicable to nontubular structures. Conveniently the instrumentation means is pre-programmed with data denoting the frequency spectrum of a structure to be tested when that structure is air filled or known to be crack free and the instrumentation means effects a determination of whether or not the structure under test is air or water filled or cracked on a comparative basis. The present invention also provides a method of testing under water structures comprising clamping a test jig to the structure, mechanically impacting the surface of the structure by hammer means mounted in the jig, sensing the vibration signal generated by means of a sensor mounted in the jig, and comparing characteristics of that signal with characteristics of a predetermined vibration signal. With the method and apparatus of the present invention there is no requirement for manipulative control of the test jig with any great precision but it is preferred that the hammer means and the sensor are relatively close together and that at least the sensor is capable of being held against the structure under test either resiliently by springs or hydraulically and it is for this latter reason that the clamp means are provided. CLAIMS
1. Apparatus for testing of underwater structures, said apparatus comprising a remotely controlled vehicle provided with an arm fitted with clamp means for clamping the arm to a structure to be tested, and a test jig comprising hammer means and a vibration sensor, the vehicle including means for driving said hammer means to effect a mechanical impact on the structure to be tested, and instrumentation means connected to the vibration sensor for monitoring the vibration signal detected thereby.
2. Apparatus as claimed in claim 1, wherein the instrumentation means is pre-pro gramme with data denoting the frequency spectrum of the structure to be tested when that structure is air filled or known to be crack free and the instrumentation means effects a determination on a comparative basis of whether or not the structure under test is air or water filled or cracked.
3. Apparatus as claimed in either preceding claim, wherein the vibration sensor is capable of being held against the structure under test either resiliently by springs or hydraulically.
4. A method of testing underwater structures comprises clamping a test jig to the structure, mechanically impacting the surface of the structure by hammer means mounted in the jig, sensing the vibration signal generated by means of a sensor mounted in the jig, and comparing characteristics of that signal with characteristics of a predetermined vibration signal.
GB08508698A 1985-04-03 1985-04-03 Testing of underwater structures by their vibration characteristic Withdrawn GB2173310A (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
GB08508698A GB2173310A (en) 1985-04-03 1985-04-03 Testing of underwater structures by their vibration characteristic

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
GB08508698A GB2173310A (en) 1985-04-03 1985-04-03 Testing of underwater structures by their vibration characteristic

Publications (2)

Publication Number Publication Date
GB8508698D0 GB8508698D0 (en) 1985-05-09
GB2173310A true GB2173310A (en) 1986-10-08

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GB08508698A Withdrawn GB2173310A (en) 1985-04-03 1985-04-03 Testing of underwater structures by their vibration characteristic

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GB (1) GB2173310A (en)

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2197473A (en) * 1986-10-31 1988-05-18 Helitune Limited Method and apparatus for vibration testing equipment
EP0379622A1 (en) * 1986-03-11 1990-08-01 Powertech Labs Inc. Apparatus and method for testing wooden poles
GB2278198A (en) * 1993-05-20 1994-11-23 Mini Agriculture & Fisheries Condition indicator
EP0832429A1 (en) * 1995-06-07 1998-04-01 Washington University Method and apparatus for predicting structural integrity by estimating modal damping factor
FR2790326A1 (en) * 1999-02-25 2000-09-01 Framatome Sa Monitoring centering pin lock in nuclear Pressurized Water Reactor fuel assemblies comprises applying shock to pin and registering signal detected by vibration sensor
GB2366382A (en) * 2000-08-23 2002-03-06 Mecon Ltd Remote monitoring of structure condition

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2083913A (en) * 1980-09-12 1982-03-31 Syminex Sa Method and device for detecting changes in the mechanical state of the members of a structure implanted in the sea
EP0056772A1 (en) * 1981-01-20 1982-07-28 Societe Bretonne De Fonderie Et De Mecanique (Sbfm) Apparatus for monitoring resonance
GB2136569A (en) * 1983-03-05 1984-09-19 Robert Joseph Savage Testing of structures
GB2137347A (en) * 1983-03-31 1984-10-03 Nat Res Dev Improvements in or relating to the testing of structures by impact

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2083913A (en) * 1980-09-12 1982-03-31 Syminex Sa Method and device for detecting changes in the mechanical state of the members of a structure implanted in the sea
EP0056772A1 (en) * 1981-01-20 1982-07-28 Societe Bretonne De Fonderie Et De Mecanique (Sbfm) Apparatus for monitoring resonance
GB2136569A (en) * 1983-03-05 1984-09-19 Robert Joseph Savage Testing of structures
GB2137347A (en) * 1983-03-31 1984-10-03 Nat Res Dev Improvements in or relating to the testing of structures by impact

Cited By (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0379622A1 (en) * 1986-03-11 1990-08-01 Powertech Labs Inc. Apparatus and method for testing wooden poles
GB2197473A (en) * 1986-10-31 1988-05-18 Helitune Limited Method and apparatus for vibration testing equipment
GB2278198A (en) * 1993-05-20 1994-11-23 Mini Agriculture & Fisheries Condition indicator
EP0832429A1 (en) * 1995-06-07 1998-04-01 Washington University Method and apparatus for predicting structural integrity by estimating modal damping factor
EP0832429A4 (en) * 1995-06-07 2000-07-19 Univ Washington Method and apparatus for predicting structural integrity by estimating modal damping factor
FR2790326A1 (en) * 1999-02-25 2000-09-01 Framatome Sa Monitoring centering pin lock in nuclear Pressurized Water Reactor fuel assemblies comprises applying shock to pin and registering signal detected by vibration sensor
GB2366382A (en) * 2000-08-23 2002-03-06 Mecon Ltd Remote monitoring of structure condition

Also Published As

Publication number Publication date
GB8508698D0 (en) 1985-05-09

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