Copyright
James F Jenkins.

Inspection of objects retrieved from the deep ocean : AUTEC acoustic array online

. (page 1 of 3)
Online LibraryJames F JenkinsInspection of objects retrieved from the deep ocean : AUTEC acoustic array → online text (page 1 of 3)
Font size
QR-code for this ebook


r/V- I4-Z-4-



Technical Note N-1424



INSPECTION OF OBJECTS RETRIEVED FROM THE DEEP OCEAN - AUTEC
ACOUSTIC ARRAY



by



J. F. Jenkins



February 1976




Sponsored by

NAVAL FACILITIES ENGINEERING COMMAND



Approved for public release; distribution unlimited.



CIVIL ENGINEERING LABORATORY

Naval Construction Battalion Center

Port Hueneme, California 93043



I A

.MS



o..



Unclassified



SECURITY CLASSIFICATION OF THIS PAGE (When Dero En



REPORT DOCUMENTATION PAGE



V REPORT NUN

TN-1424



2. GOVT ACCESSION NO

DN487017



3 RECIPIENT'S CAT ALOG NUMBEF



4. Tn\.E (and Subtitle)

INSPECTION OF OBJECTS RETRIEVED FROM
THE DEEP OCEAN - AUTEC ACOUSTIC ARRAY



5. TYPE OF REPORT & PERIOD COVERED

Not final; Feb 1973 - Oct 1973



6. PERFORMING ORG. REPORT NUMBER



AUTHORfsJ

J. F. Jenkins



CONTRACT OR GRANT



9. PERFORMING ORGANIZATION NAME AND ADDRESS

CIVIL ENGINEERING LABORATORY

Naval Construction Battalion Center
Port Hueneme, California 93043



O&M, N
42-016



II. CONTROLLING OFFICE I



Chesapeake Division, Naval Facilities Engineering
Command, Washington Navy Yard, Washington,
DC 20374



12. REPORT DATE

February 1976



23



3ER OF PAGES



4, MONITORING AGENCY NAME a ADDRESSrif £



' Irom Co^t^olIir^(i Office)



15. SECURITY CLASS, fo

Unclassified



15a. DECLASSIFICATION DOWNGRADING
SCHEDULE



6. DISTRIBUTION ST ATEMEN J (of thi b- Report)

Approved for public release; distribution unlimited.



DISTRIBUTION STATEMENT (of I



in BJock 20, if different from Report)



18 SUPPLEMENTARY NOTES



19. KEY WORDS (Continue on reverse side if necessary and identify by btoclr number;

Corrosion, metals, alloys, seawater, wire rope, electromechanical cables, cable
terminations, underwater structures, steel, galvanized steel, aluminum alloys,
copper-nickel alloys, nickel-copper alloys, inspection techniques.



20. ABSTRACT (Contin



Information on the corrosion of materials exposed to marine environments must be
obtained if ocean structures are to be designed with predictable lifetimes. A large amount
of relevant information can be obtained at a relatively low cost by evaluating the condition
of objects retrieved from the sea. To optimize these evaluations, they must be performed
logically and uniformly. Development and application of guidelines for such evaluations

continued



DD 1 JAN 73 1473 EDITION OF I NOV 65 IS OBSOLETE



MBL/WHOI



Unclassified



SECURITY CLASSIFICATION OF THIS PAGE (UTien Data Entered)



D3D1 ODMDSm S



Unclassified



SECURITY CLASSIFICATION OF THIS PAGEfXTion D»(a Entered)



20. Continued

can provide this optimization. As a part of the development of guidelines, this report
describes an evaluation of the AUTEC acoustic array emplaced in 1962 and retrieved from
the Tongue-of-the-Ocean, Bahama Islands, after 12 years of exposure. The condition of
the array as well as the application and revision of the inspection guidelines are discussed.



Library Card



Civil Engineering Laboratory

INSPECTION OF OBJECTS RETRIEVED FROM THE
DEEP OCEAN - AUTEC ACOUSTIC ARRAY, by J. F.
Jenkins

TN-1424 23ppillus February 1976 Unclassified

1. Underwater structures 2. Corrosion I. 42-016

Information on the corrosion of materials exposed to marine environments must be
obtained if ocean structures are to be designed with predictable lifetimes. A large amount of
relevant information can be obtained at a relatively low cost by evaluating the condition of
objects retrieved from the sea. To optimize these evaluations, they must be performed
logically and uniformly. Development and application of guidelines for such evaluations
can provide this optimization. As a part of the development of guidelines, this report
describes an evaluation of the AUTEC acoustic array emplaced in 1962 and retrieved from
the Tongue-of-the-Ocean, Bahama Islands, after 12 years of exposure. The condition of the
array as well as the application and revision of the inspection guidelines are discussed.



I I



Unclassified



CONTENTS

Page

INTRODUCTION 1

AREIAY RECOVERY DESCRIPTION 2

FIELD INSPECTION 2

Visual Observations of Replacement Acoustic String 3

Visual Observations of Failed Array Upper Buoy 3

Electromechanical (21 -Quad) Cable 4

Cable Termination Housings 4

Hydrophone Cases 5

Tracking Arm Assembly 5

Array Counterweight Cable 6

LABORATORY EVALUATION. . . 6

Evaluation of Tracking Arm Joints 6

Analysis of Corrosion Products 7

RESULTS OF INSPECTION, SAMPLE EVALUATION, AND RECOMMENDATIONS. ... 7

EVALUATION OF GUIDELINES FOR INSPECTION OF OBJECTS

RECOVERED FROM THE SEA 7

CONCLUSIONS 8

Appendix A — Guidelines for Inspection of Structures Recovered

From the Sea 10

Appendix B - Guidelines for Inspection of Structures Recovered

From the Sea 15

REFERENCES 22

LIST OF ILLUSTRATIONS
Figure 1 . AUTEC acoustic array 9



INTRODUCTION

In order to gather information on the performance of materials as
structural components of fixed ocean facilities the Criteria and Methods
Program of the Chesapeake Division (CHESDIV) , NAVFAC has initiated a
project to develop and apply techniques to maximize the amount, quality,
and applicability of data obtained from the inspection of objects retrieved
from the ocean. In order to develop techniques to maximize the benefit
of these inspections, guidelines for the inspection of structures recovered
from the sea have been prepared, exercised, and, as appropriate, revised.
The main purpose of these guidelines is to set forth procedures for
inspection of objects recovered from the sea which can be uniformly
applied by field personnel with limited expertise in the field of marine
corrosion and which will result in the accumulation of data which can be
compared with data obtained by other field personnel from inspection of
other objects. The gathering of information in this manner is cost
effective when compared with normal corrosion testing because the costs
of specimen procurement, specimen preparation, specimen exposure, and
specimen retrieval, which are a large portion of the cost of most
marine corrosion testing, are eliminated. An additional advantage of
gathering information in this manner is that actual components of ocean
structures are evaluated. The major disadvantage of data gathered in
this manner is that, due to incomplete documentation of the structure
prior to emplacement, the data are normally of a qualitative or semi-
quantitative nature. Quantitative data such as corrosion rates are not
normally obtainable from such inspections.

In order both to validate the guidelines for inspection of objects
recovered from the sea and to gather preliminary data on the performance
of materials as structural components of fixed ocean facilities,
CHESDIVNAVFAC has sponsored the inspection of "objects of opportunity"
recovered from the sea.

One such object was the AUTEC acoustic array, portions of which
were retrieved from the Tongue-of -the-Ocean, Bahama Islands, in March
1974 for repair and refurbishment.

In addition to the validation of inspection guidelines and gathering
of material performance data, the field inspection of the retrieved
portion of the array was intended to assist in the determination of the
extent to which undamaged or unrecovered portions of the existing array
could be utilized in the refurbished array. Also, during a precruise
standby period, a replacement acoustic string was cursorily inspected
after retrieval from a 6-month test exposure in Ft. Lauderdale, Florida,
Harbor.



This report is a description of the inspection and evaluation of
the replacement array, the AUTEC array after retrieval, an outline of
the results of the inspections and evaluations, and a discussion of the
application and revision of the inspection guidelines.



ARRAY RECOVERY DESCRIPTION

As shown in Figure 1, the AUTEC acoustic array emp laced in 1962,
consists of two main parts: the deep water mooring and the acoustic
string. The system was so designed that the acoustic string could be
retrieved and replaced without retrieving the deep water mooring. In
December 1973 the upper buoy was found washed ashore. The 21 -quad cable
used in the acoustic string had parted at or near the cable termination
on the second termination below the main buoy. It was determined during
an inspection of the failed array using a manned submersible that the
acoustic string had fallen on the main mooring buoy. It was then planned
to retrieve the acoustic string by attaching to the bitter end of the
failed 21 -quad cable, raising the bitter end to the surface, and then
retrieving the acoustic string in a normal manner. It was planned to
replace the failed acoustic string with a new unit if the condition of
the deep water mooring, as inferred from the condition of the failed
acoustic string, could be expected to have a reasonable additional
service life.

During 11 days of at- sea operation 1,200 feet of electromechanical
(21 -quad) cable, nine hydrophones, two acoustic beacons, an underwater
communications transducer (UQC) and the tracking arm assembly were
retrieved by the primary recovery vessel, the R. V. Hunt. As deck space
on the E. V. Hunt was limited, the cable, hydrophones, beacons, and UQC
were transferred to an auxiliary recovery vessel, the J. W. Pierce^ for
inspection. The tracking arm assembly was too large to safely transfer
at sea, and it was inspected on the B. V. Hunt.



FIELD INSPECTION

The field inspection, following the guidelines included as Appendix
A to this report, was made by an experienced corrosion engineer of the
Navy's Civil Engineering Laboratory. A professional photographer from
Lockheed Electronics Co. , together with an assistant, was responsible
for the retrieval and inspection photography. Technical assistance for
the inspection was furnished by personnel from the Naval Underwater
Systems Center, and the Naval Ship Research and Development Center.
Mechanical assistance was furnished by the crew of the recovery vessels
belonging to Traaor MAS. All inspection equipment and supplies as
outlined in Appendix A, except for the crating materials, were available
on site.



Visual Observations of Replacement Acoustic String

The replacement acoustic string was retrieved from Ft. Lauderdale
Harbor for inspection after 6 months of exposure. The corrosion behavior
of this string was of interest not only because it was to replace the
failed acoustic string, but because many of the materials used in the
new string were the same as those used in the failed string. Corrosion
effects noted on the replacement string could therefore be used to
determine which areas of the failed array should be inspected in detail.

The most severely corroded portions of the replacement string were
the Monel 400 bands used to secure the rubber hydrophone boots to the
hydrophone cases. Most of the bands were severely corroded due to
crevice corrosion at the band- joining buckles. Many of the bands had
failed completely. The 90-10 cupro-nickel hydrophone cases were very
slightly etched. The electromechanical cable was unattacked. The
painted steel portions of the replacement string were unattacked except
for areas where the steel was exposed by abrasion. The protective
coatings used were essentially intact except where mechanically damaged.

Visual Observations of Failed Array Upper Buoy

The upper buoy had been only slightly damaged by being washed'
ashore. Nearly all surfaces of the assembly were covered with a thick ■
(1/8-inch to 1/4-inch) accumulation of encrusting coral. Fresh mechanical
damage to the structure could be easily identified by the lack of encrusting,
coral on the surface at the point of damage. The steel tube support
structure was corroded slightly at a few areas of paint failure, particularly
on the top sides of the structural members. This could have been due to
personnel climbing on the structure prior to deplo3mient. The four steel-
buoyancy spheres had a few areas of minor pitting up to 1/8-inch deep.
The paint coating, where visible due to the flaking off of the encrusting
coral, was reasonably intact and relatively free from blistering, flaking,,
or chalking .

The electromechanical cable termination at the base of the buoy
had been previously disassembled and details of its condition upon
retrieval were not well documented. However, as for many of the other
terminations retrieved and inspected, the minimum diameter of each armor
wire was measured upon disassembly and was recorded. This information
was used by NSRDC in evaluating the condition of the terminations in an
attempt to infer the condition of the terminations which were not
recovered.



*

In this report all points where the armor wires are

discontinuous are referred to as terminations, even

when the termination is used only as an electrical

conductor breakout.



Electromechanical (21 -Quad) Cable

The cable had parted at the upper end of the second breakout housing
below the upper buoy. The failed end of the cable showed significant
corrosion of most of the outer and inner armor wires. The attack was
localized at the areas of the wire where the polyethylene jacketing on
the individual wires had been removed in assembling the terminations.
The galvanized coating on the wires was intact under the polyethylene ■
jacketing but was not present on most of the wires adjacent to the point
of failure.

The only significant corrosion of the entire 1 ,200-f oot-long section
of electromechanical cable retrieved was at the cable terminations.
This attack was localized adjacent to and just Inside the outer edge of
the wire-retaining slots in the termination. At these areas the protective
polyethylene jacket had been removed from the wires in order to assemble
the termination. The corrosion preventive compound used to fill the
interior of the termination housings was, in most cases, not present in
this critical area. There was a general trend for the presence of more
of this corrosion preventive compound in those housings exposed at a
greater depth on the array. In order to quantitatively evaluate the
condition of the electromechanical cable at the terminations thirteen
terminations were disassembled for inspection. The minimum diameter of
each wire was measured. The data from these measurements was analyzed
by NUSC in an attempt to predict the remaining life of the unrecovered
cable at the terminations. The only trend noted in a field evaluation
of this data was that the wires, particularly the inner armor wires,
were less corroded in those terminations which had retained a large
amount of corrosion preventive compound than in those terminations which
had retained little corrosion preventive compound. As noted above, '
retention of this compound was generally, but not reliably, a function
of depth. It was noted during these inspections that approximately 50%
of the wires were not properly seated in the termination block. Eleven
terminations and a 25- foot section of cable were retained by NUSC and
NSRDC for further analysis.

Cable Termination Housings

The steel termination housings were in good to fair condition. The
most severe attack was on the end sleeves. However, penetration of
these end sleeves (1/8-inch original thickness) was noted in only two
cases. A thin, patchy deposit of copper was noted on the surfaces of/
miany of the housings. This was most probably due to substitution of
electrogalvanizing for hot-dip galvanizing on the housings. Electro-
galvanizing generally employs a thin copper plating, or flash, over the
steel to promote good adhesion of the electrodeposited zinc coating.
This copper deposit can, and probably did, lead to galvanic attack of
the portions of the housing which did not originally have, or did not
retain, the copper deposit. As no copper deposits were found on the end



sleeves the fact that these portions of the housings were more severely
attacked than the housing bodies can be explained by this effect.

Hydrophone Cases

The hydrophone cases were fabricated from either 90-10 cupro-nickel
or 70-30 cupro-nickel. The 90-10 cupro-nickel housings were uniformly
etched and had a thin blue-green patina on much of their surfaces. The
weld beads and heat-affected zones were in the same condition as the
remainder of the housings. No difference in attack was noted in the
housings exposed at different depths.

The hydrophone cases fabricated from 70-30 cupro-nickel were also
uniformly corroded except for some shallow linear attack in the heavily
deformed hydrophone support tubes. No accelerated weldment attack was
noted.

All the monel bands used to secure the protective rubber boots to
the hydrophone supports showed some signs of crevice corrosion, particularly
at the band joining buckles. Two bands were found to have completely
failed.

The insulating blocks used to electrically isolate the hydrophone
cases and other copper-alloy instrument cases from their respective
steel termination housings had retained their original effectiveness.
Resistance between the cases and the housings was in excess of 1,000
ohms.

Tracking Arm Assembly

The tracking arm assembly consisted of a steel center section with
aluminum outer sections. The steel center section was covered with a
very thin layer of tan corrosion products as is typical of the corrosion
products on galvanized steel after depletion of the zinc coating. No
copper deposits were noted on the steel structure. No significant
corrosion of the steel structure was evident. At the ends of the open
tubular sections of the central portion of the tracking arm assembly
there were stalactite like rust tuber cules. These tubercules were up to
8 inches long and 2 inches in diameter. Their hard outer skins (1/4-
inch thick) covered softer and often fluid interiors. After several
hours exposure to the air the tubercules became brittle and crumbled.
The interior portions of the tubular steel members which showed these
tubercules were uniformly corroded.

The aluminum sections of the tracking arm assembly were heavily
corroded. This corrosion was most severe on the portions of these
sections nearest the steel center section. As the aluminum and steel
were separated by nonmetallic isolation blocks which had retained an
insulation resistance of over 1,000 ohms between the steel and aluminum
sections, galvanic corrosion between the dissimilar metal sections was
not the cause of this localization of attack. There were, however, red
deposits on the central portions of the aluminum tracking arms. The



electromechanical cable just above the tracking arm assembly was heavily
coated with copper-based antifouling compound. The red deposits were
assumed to be copper (which was later verified) which would explain the
localization of the attack of the aluminum structure most directly
beneath the source of copper. The aluminum structure in electrical
contact with the 70-30 cupro-nickel hydrophone cases at the ends of the
tracking arms was severely corroded by galvanic action.

Array Counterweight Cable

Approximately 10 feet of the 3.75-inch wire rope array counterweight
cable was available for inspection. The outer wires were 100% rusted.
However, corrosion of these wires was not severe. No broken wires were
located. The inner strands of the cable had retained much of their
original lubricant coating. The inner strands of the cable were essentially
uncorroded.



LABORATORY EVALUATION

Samples of joints from both the steel and aluminum portions of the
tracking arm assembly were returned to CEL for analysis. Also, several
samples of corrosion products from various portions of the array and
several small hardware items were retained by CEL for analysis. -

Evaluation of Tracking Arm Joints

The aluminum tracking arm joint was analyzed chemically and found
to be aluminum alloy 6061 . Chemical analysis of the weld metal was
typical of deposits obtained with 5356 welding wire. The maximum pit
depth measured on this section was 0. 200 inch. The pits were randomly
distributed with a frequency of ssl pit per square inch. Microstructural -
analysis showed these pits to be intergranular in nature. The weld
beads were less corroded than the adjacent parent metal. There was no .
accelerated attack at the heat-affected zones adjacent to the welds. It ,
was noted, however, that corrosion was accelerated at areas which had
been covered with electrical tape during exposure. Mechanical tests of
the section resulted in failures of the tubular sections; the weld
joints did not fail. The ultimate strength of the tube sections averaged'
56% of the rated breaking strength of unexposed 6061 -T6 tube. However,
the elongation was reduced from a rated 12% to an average of 4%. This
reduction of elongation is typical of aluminum alloys which are subject
to pitting.

The steel section of the structure was analyzed chemically and
found to be typical of A- 36 structural steel. The section was corroded
uniformly. Tensile tests of coupons from the tubes showed no loss of
material properties compared with typical properties of A-36 steel.



Analysis of Corrosion Products

Analysis of corrosion products removed from various array components
identified their major constituents to be as follows.

1. from 70-30 Cupro-nickel hydrophone cases: Ni(OH) , CuCI

2. from 90-10 Cupro-nickel hydrophone cases: Ni(OH) , CuCI , CuO

3. red material from aluminum tracking arm section: Metallic Cu,
Cu 0, amorphous A1 -XH 0, NaCI , Metallic Al

4. Corrosion products from monel bands: CuC1„, CuO, Ni (OH)

RESULTS OF INSPECTION, SAMPLE EVALUATION, AND RECOMMENDATIONS

Considering the duration of exposure, the array was in remarkably
good condition. Except for the corrosion of the armor wires of the
electromechanical cable at the terminations, the galvanic corrosion
between the aluminum tracking arm sections and the hydrophone cases, the
corrosion of the aluminum tracking arm sections due to copper ion
contamination, and the crevice corrosion of the monel bands on the
hydrophone boots there was little significant corrosion of the array.
The aforementioned corrosion problems can be avoided by changes in future
designs.

The electromechanical cable terminations can be augmented with
flexible boots to retain the corrosion preventive compound in the critical
area where the protective jacketing is removed from the wires. The
galvanic corrosion between the hydrophone cases and the aluminum tracking
arm section can be eliminated by electrical isolation such as that used
in the steel /aluminum joint on the tracking arm assembly. The copper
ion contamination- caused corrosion of the aluminum tracking arm sections
can be avoided by eliminating heavy metal (copper, mercury) antifoulants
from the vicinity of bare aluminum structures. The antifoulants are not
generally needed in the deep ocean to prevent the heavy accumulation of
fouling organisms normally encountered in shallow ocean environments.
The crevice corrosion of the monel bands can be reliably eliminated
either by selection of an alternate material resistant to crevice
corrosion or by cathodic protection of the monel bands.



EVALUATION OF GUIDELINES FOR INSPECTION OF OBJECTS
RECOVERED FROM THE SEA

The interim guidelines for inspection of objects recovered from the
sea (Appendix A) were found to be technically applicable to the evaluation
of the AUTEC array. The guidelines were useful in explaining to the
recovery team what was planned for the inspection and for giving personnel
assisting in the inspection an overview of the procedures to be used.



However, it was determined that the guidelines presented in Appendix A
did not cover an essential, in fact crucial, part of the inspection -
prerecovery planning.

The interim guidelines were, therefore, revised to include a section
on prerecovery planning. These revised guidelines are included as
Appendix B of this report and should, until superseded, be used as new
interim guidelines for the future inspection of structures recovered
from the sea.



CONCLUSIONS

By a systematic evaluation of objects recovered from the sea, data
obtained can be used for predicting the additional useful life of the
object, modifying the existing object to extend its life, or designing
new ocean structures. The usefulness of these data can be maximized by
application of standardized guidelines for inspection of such objects.
The interim guidelines presented in Appendix A were found to be technically
applicable but deficient in coverage of prerecovery planning. Appendix
A is included in the report to document the procedures used to obtain


1 3

Online LibraryJames F JenkinsInspection of objects retrieved from the deep ocean : AUTEC acoustic array → online text (page 1 of 3)