The purpose of this chapter is to describe methods for conducting nondestructive testing (NDT) underwater and to provide general procedures and requirements for accomplishing each method. The NDT methods discussed include underwater visual testing (UWVT), underwater magnetic particle testing (UWMT) and underwater ultrasonic thickness gauging (UWUTG). Understanding the information in this chapter will facilitate effective planning and execution of underwater NDT tasks and will ensure timely return of the ship to operational readiness. This chapter is not intended to serve as a training document used to certify underwater NDT inspectors.
This chapter describes standard NDT methods that have been adapted to underwater use. The chapter addresses why and when each method is used. For each method, the chapter also discusses planning and preparation requirements, general procedures and expected results. The general procedures provided can be used to develop specific procedures for the NDT task at hand. This chapter does not replace or supersede existing technical documents that pertain to NDT, nor does it provide information on general operational and safety procedures for performing underwater ship husbandry. Definitions for words and phrases applicable to NDT can be found in MIL-STD-271 and MIL-STD-2035.
The information in this chapter can be used by anyone involved in planning and executing underwater NDT efforts. Divers can use the information for instruction in applying the various NDT methods and for recognizing equipment required by each method. Diving supervisors and NDT inspectors can use this chapter for guidance in developing an operational plan, for coordinating personnel and for monitoring underwater work for quality assurance.
NDT may be accomplished underwater using UWVT, UWMT, UWUTG or a combination of these methods. Underwater Visual Testing (UWVT) is used to verify dimensional requirements associated with underwater welding, to ensure that welds are free of various detrimental conditions and to ensure that inspection surfaces are suitable for other NDT methods. All of these uses of UWVT are more exacting than the underwater visual inspections described in NSTM Chapter 081, related to underwater fouling. Underwater Magnetic Particle Testing (UWMT) is generally used to discover or document surface breaking cracks in ferrous metal structures and, along with UWVT, is an integral part of underwater welding quality assurance. Underwater Ultrasonic Thickness Gauging (UWUTG) is generally used to discover or document the deterioration of hull plating, as part of the pre-overhaul test and inspection program.
7-1.4.1 PRELIMINARY EFFORT. The decision to conduct UWVT, UWMT or UWUTG inspections often results from a visual examination. Visual examinations range in scope from simple appraisals to determine the extent and type of marine growth found on a ship's hull, to more detailed assessments of the material condition of specific areas. Because the results obtained from a visual examination can be instrumental in determining the need for NDT and the method of NDT to be used, divers must be able to relay visual examination results to NDT inspectors, diving supervisors and repair personnel. To relay results, divers must be familiar with ship hull configurations, openings, appendages and propulsion assemblies. They must also be familiar with the abnormal conditions (table 7-1-1) which indicate that NDT may be necessary to determine the extent of damage. Divers may use underwater video cameras, still cameras, stereo cameras and various measuring devices to record the results of a visual examination.
7-1.4.2 UNDERWATER VISUAL TESTING (UWVT). Underwater visual testing (UWVT) is a nondestructive method for locating and defining surface discontinuities underwater. It is most often applied to welds, to assess their condition and conformance with dimensional requirements. UWVT must be performed with measuring devices or comparators when quantitative restrictions apply and the diver must be properly trained in the use of such devices. The diver must also be trained to recognize detrimental features associated with welding processes, as well as environmental conditions, such as limited visibility or improper lighting, that would affect the validity of the inspection.
7-1.4.2.1 UWVT Applications. Underwater visual testing is used for three distinct purposes. The first is in the underwater welding process, to verify dimensional requirements such as fit-up and that welds meet the requirements for fillet size, allowable undercut, etc. The second is to ensure that welds are free of cracks, incomplete fusion, arc strikes and other fabrication scars as specified by the controlling document. The third is to ensure the suitability of underwater surfaces for other underwater NDT methods, where improper surface conditions may cause false indications to mask relevant indications.
7-1.4.2.2 UWVT Limitations. UWVT shares the same limitations as conventional (topside) VT, but is generally more difficult to apply. The minimum size indication detectable may be larger underwater, despite the magnification inherently obtained when viewing objects in an underwater environment. Limited visibility, distortion caused by the diver's faceplate or thermal gradients and fogging of the faceplate are some of the factors that may reduce the inspection sensitivity. Limited mobility or access restricted by thermal protection or life support equipment may also reduce inspection sensitivity. The availability and quality of communications, video and photographic equipment may limit the eventual quality of records and reports.
7-1.4.2.3 UWVT Equipment. The full range of visual testing tools, including weld profile gauges, joint angle measuring devices, surface comparators, etc., must be available to the diver and used when appropriate. Tools which are adversely affected by use underwater should be considered expendable. In addition, an appropriate white light source and ground fault interrupter, such as specified in NAVSEA drawing number 6653063, shall be available.
7-1.4.3 UNDERWATER MAGNETIC PARTICLE TESTING (UWMT). Underwater magnetic particle testing (UWMT) is a nondestructive method for locating and defining surface discontinuities in magnetic materials underwater. Its principles are the same as its topside (i.e., conventional) counterpart, that is, magnetic particles are attracted to flux leakages at the surface of magnetized materials and form indications of discontinuities located either at or just below the surface.
In operation, the magnetic material or item of interest is magnetized using an electromagnetic yoke specially designed for underwater use. Wherever surface discontinuities exist within the yoke's field of influence, magnetic flux will "leak" from the surface of the part. A slurry of magnetic particles are attracted to and aligned with, the leaking magnetic flux. The particles are brightly colored and form a visible indication corresponding to the location of discontinuities at or very near the part's surface.
7-1.4.3.1 UWMT Applications. Underwater magnetic particle testing is used primarily as a quality assurance tool to support underwater welding on ship structures. It can be used as well to inspect hulls or other magnetic components for surface discontinuities such as cracks and lack of fusion. UWMT may also be used to define the true length (and locate the true ends) of discontinuities detected visually and to help determine where corrective measures (e.g., stop drilling) should be applied.
7-1.4.3.2 UWMT Limitations. As with any inspection method, UWMT has some limitations. These include:
a. Underwater magnetic particle testing has limited sub-surface capability. For use on U.S. Navy applications, it is considered to be strictly a method for detecting and measuring surface discontinuities. It is not an approved method for detection of sub-surface discontinuities.
b. The adequacy of inspection with UWMT (as with most nondestructive test methods) is largely a function of the operator's knowledge and skill. Inspections with UWMT are to be performed only by personnel trained and certified specifically in UWMT. (See Section 7-2.2.9 for certification requirements).
c. UWMT is limited to ferromagnetic materials, which include most steels. For most applications, a simple check with a magnet is sufficient to determine suitability for UWMT.
7-1.4.3.3 UWMT Equipment. For fleet users, the equipment for UWMT is specified in NAVSEA drawing number 6653063. This equipment meets the requirements of MIL-STD-271. Only this equipment may be used. Major components of the UWMT system include:
1. Underwater magnetic yoke with articulated legs
2. White light source
3. Underwater magnetic particles
4. Ground fault interrupter
5. Magnetic field indicator
6. Flaw size sensitivity plate.
For non-fleet users, the UWMT equipment shall meet the requirements of MIL-STD-271.
7-1.4.4 UNDERWATER ULTRASONIC THICKNESS GAUGING (UWUTG). Underwater ultrasonic thickness gauging (UWUTG) is a nondestructive method for measuring the thickness of ships' hulls. Its principles are the same as its topside (i.e., conventional) counterpart - the time of travel of ultrasonic emissions from a hand-held ultrasonic transducer are measured and converted to thickness based on the (known) velocity of sound in the material being tested. In UWUTG, the ultrasonic instrument is located topside and is monitored by a certified ultrasonic test inspector, while the transducer is manipulated along the hull by a diver working under the direction of the inspector. For fleet users, a computer data acquisition system is used, which permits area scanning and rapid data collection and which prints out minimum, maximum and average thicknesses measured.
7-1.4.4.1 UWUTG Applications. The UWUTG technique is suitable for measuring thicknesses of approximately 1/4 inch to 2 inches in steel and ultrasonically comparable materials. It works best on surfaces which are approximately parallel but can be used on surfaces which are corroded or pitted on one or both sides.
7-1.4.4.2 UWUTG Limitations. As with conventional ultrasonic techniques, the degree of difficulty in obtaining accurate readings increases with the degree of surface roughness. Ideal conditions are smooth front and back surfaces; worst-case conditions are very rough or pitted front and back surfaces. In the latter case, the scanning speed may need to be reduced significantly in order to obtain accurate readings. Under conditions of extreme pitting on both surfaces, UWUTG may be unable to provide accurate readings.
7-1.4.4.3 UWUTG Equipment. For fleet users, the equipment for UWUTG is specified in NAVSEA drawing number 6653028. This equipment meets the requirements of MIL-STD-271. Major components of the UWUTG system include:
1. Ultrasonic test instrument
2. Transducer
3. Computer
4. Ground fault interrupter
5. Hogging lines
6. Software
7. Step block
8. Waterproof cables
For fleet users, only this equipment may be used, with the following exceptions:
a. Rigging lines: The UWUTG system includes a set of rigging lines for positioning the diver. These rigging lines are designed to meet most applications but can be modified (or another location system can be used) if desired to better suit the particular user or application. Any changes must be reviewed and accepted by the Level II Inspector.
b. Calibration blocks: The UWUTG system includes two calibration blocks and the software will default to those step block settings if they are not otherwise defined. However, if an activity desires to use different calibration blocks with UWUTG, such use is permitted provided the blocks used meet the requirements of MIL-STD-271.
For non-fleet users, UWUTG equipment shall meet the requirements of MIL-STD-271.
Planning for nondestructive testing (NDT) requires an in-depth review of various source documents, such as previous inspection reports, hull cleaning reports and engineering drawings that identify the materials used and the construction criteria of the specific area of inspection. Each document has a unique purpose; therefore, all available references must be consulted before and during each task. This section identifies important source documents and the information relevant to NDT that each document provides. For direction on obtaining and using reference materials, refer to Chapter 2 of this manual, General Information and Safety Precautions.
7-2.1.1 U.S. NAVY DIVING MANUAL. NAVSEA 0994-LP-001-9010, U.S. NAVY DIVING MANUAL, Volume 1, Air Diving, provides guidance, instructions and safety precautions for diving operations.
7-2.1.2 NAVAL SHIPS' TECHNICAL MANUAL (NSTM). The purpose of S9086-00-STM-000, Naval Ships' Technical Manual (NSTM), is to provide technical information to personnel engaged in the supervision, operation or maintenance of U.S. Navy Ships. The various chapters and volumes of the NSTM contain detailed administrative and technical instructions that amplify U.S. Navy Regulations and other authoritative documents. These instructions are designed to assist personnel, afloat and ashore, in satisfactorily managing the operation and maintenance of ships and shipboard machinery and equipment. The NSTM chapters listed below contain information of special interest to NDT planners. While the NSTM chapters described below contain a wide range of information, the following descriptions are limited to information relevant to NDT.
050 Readiness and Care of Inactive Ships. This chapter discusses preservation and routine inspection programs for inactive ships' hulls.
074 Volume 1, Welding and Allied Processes; and Volume 2, Nondestructive Testing of Metals-Qualification and Certification Requirements for Naval Personnel. This chapter provides the minimum mandatory requirements and guidance for welding, brazing, NDT and safety used for ship maintenance. Volume 1 is useful in identifying improper welds and familiarizing personnel with welding terminology. Volume 2 addresses NDT qualification and certification of naval personnel.
080 Publications and Drawings. This chapter discusses the various systems used to store information, the particular information each system contains and the requisitioning of information.
081 Waterborne Underwater Hull Cleaning of Navy Ships. This chapter provides guidance on criteria for evaluating fouling severity and antifouling and anticorrosive paint condition; determining intervals of cleaning; and selecting cleaning methods and equipment to be used.
090 Inspections, Tests, Records and Reports. This chapter discusses types of corrosion and their causes and identifies critical inspection areas.
091 Submarine Hull Inspection. This chapter furnishes submarine hull integrity inspection, repair and reporting requirements.
100 Hull Structures. This chapter discusses inspection and repair requirements for ships' hulls and superstructures.
631 Preservation of Ships in Service (Surface Preparation and Painting). This chapter provides precautions the diver must take when removing organotin paints from ships' hulls. It also discusses safety precautions for topside operation of hydroblasting equipment.
633 Cathodic Protection. This chapter provides information on the equipment, design, installation, operation and maintenance of cathodic protection systems used on active Navy ships, submarines, boats and craft. It discusses the requirement for periodic diver inspections to: detect abnormal hull conditions, ensure adequate cathodic protection system operation and assess the cathodic protection system performance.
9430 Shafting, Bearings and Seals. This chapter furnishes descriptive visual evidence of and repair requirements for deterioration, physical damage, lack of adhesion and other discontinuities to rubber and fiberglass covered shafts.
7-2.1.3 SHIP DRAWINGS. Ship drawings are the primary source of engineering data required for underwater ship husbandry (UWSH). Ship drawings define the configuration, arrangement and dimensions of a ship's structure and its components. They provide UWSH personnel with the locations, dimensions and interfaces of all underwater components such as hull plating, structural members, propulsion gear, rudders, hull appendages and hull openings. Ship drawings also specify types of material used and list materials and parts for each ship system. The ship drawings listed below are pertinent to NDT.
7-2.1.3.1 Docking Plans. The ship docking plan provides an underwater profile of the ship, the plan view of its bottom and the exact locations of all underwater appendages with reference points and measurements. The docking plan also provides vertical measurements taken from the main deck and from the baseline.
7-2.1.3.2 Shell Plate Expansion. Shell plate expansions provide detailed information on individual hull plate locations, materials used, construction details, and design plating thickness. Inspectors and diving supervisors can use the information to develop specific procedures for the area being inspected.
7-2.1.3.3 Shafting Arrangement Drawing. The shafting arrangement drawing shows the locations of all the propulsion shafting components from the propeller to the reduction gear connection. The drawing also gives shaft measurements and clearances around shafting components.
7-2.1.3.4 Component-Level Drawing. Drawings of a component being inspected or of components in an inspection area will specify construction conditions such as dimensions, base material and surface finishes of the component or components.
7-2.1.3.5 General Outboard Profile. The General Outboard Profile provides visual landmarks between the water line and the 01 deck that can be used to locate specific frame numbers. The diving supervisor can direct hogging line placement or position the dive boat with respect to these above-water features.
7-2.1.4 MILITARY STANDARDS. Military standards contain minimum requirements for performing various activities. Those which are most often used in the inspection and repair of ships are listed below.
7-2.1.4.1 Fabrication, Welding and Inspection of Ships Structure. MIL-STD-1689 contains minimum requirements for the fabrication and inspection of the hull and associated structures of combatant surface ships. This includes requirements for shipbuilding, materials, welding, welding design, mechanical fasteners, workmanship and inspection.
7-2.1.4.2 Requirements for Nondestructive Testing Methods. MIL-STD-271 discusses how to determine the presence of surface and internal discontinuities in metals. It also contains the minimum requirements necessary to qualify NDT procedures, equipment and civilian personnel.
7-2.1.4.3 Nondestructive Testing Acceptance Criteria. MIL-STD-2035 contains acceptance criteria for determining the acceptability of nondestructive test discontinuities in materials and components used by the Naval Sea Systems Command (NAVSEA) and tested in accordance with the methods described in MIL-STD-271.
7-2.1.5 DIVING EQUIPMENT AUTHORIZED FOR NAVY USE (ANU). NAVSEAINST 10560.2, ANU, denotes selected commercially available diving equipment, tools, accessories and hyperbaric system components which have undergone design safety reviews, test and evaluation or both, to ensure diver safety.
Chapter 2 of this manual, General Information and Safety Precautions, contains general planning guidelines. This chapter discusses general planning requirements that include personnel, equipment, procedures and quality assurance (QA) for developing an operational plan to conduct underwater NDT. This chapter also contains planning requirements specific to underwater visual testing (UWVT), underwater magnetic particle testing (UWMT) and underwater ultrasonic thickness gauging (UWUTG).
7-2.2.1 OPERATIONAL PLAN. Before undertaking any NDT operation, the NDT inspector, diving supervisor and repair officer should develop a comprehensive, written operational plan that includes detailed procedures for the NDT tasks involved. The plan should include:
a. Documents pertinent to planning the operation, including identification of the area(s) to be inspected and, for UWUTG, the size of the inspection grid.
b. Personnel training and certification requirements
c. Responsibility assignments for all involved activities
d. Required tools, equipment and expendable materials
e. Detailed step-by-step procedures for performing NDT underwater
f. QA package with specific inspection and verification (I&V) points
g. Post-operational procedures
h. Safety precautions.
7-2.2.2 REFERENCE DOCUMENTS. For information on identifying NDT reference documents needed for planning, see paragraph 7-2.1.4. See Chapter 2 of this manual for information on obtaining and using reference documents.
7-2.2.3 EQUIPMENT, TOOLS and MATERIALS. The equipment, tools and materials needed to accomplish NDT can be determined from the information provided in this chapter. When special equipment, tools and materials are needed, procurement or fabrication arrangements should be developed and the sources and lead times should be incorporated into the operational plan. NDT equipment and materials must meet the requirements set forth in MIL-STD-271 and this document.
7-2.2.4 DETAILED PROCEDURES. A NAVSEA approved procedure is required before performing UWVT, UWMT or UWUTG. In the case of UWVT and UWMT, sample procedures are provided as Appendix C and D of this document. These samples have NAVSEA approval. If desired, the activity performing UWVT or UWMT may elect to utilize either (or both) of these procedures (unaltered) by including it with the appropriate signed cover sheet. Otherwise, the activity must establish its own procedure and submit it for NAVSEA approval.
7-2.2.5 QUALITY ASSURANCE PACKAGE. QA requirements for NDT must be determined before beginning the task. Local regulations should specify a format for preparing a QA package or one may be developed for the particular underwater NDT operation. The QA package developed for each NDT operation will be specific to that operation and can range from a separate QA plan to a QA checklist or worksheet incorporated into the operational plan. The package should include a set of designated inspection and verification (I&V) points and provide space for personnel to document that QA standards have been met before proceeding from one step to the next in the NDT procedures. Appendixes A and B provide the minimum information requirements for QA forms with designated I&V points for UWVT/UWMT and UWUTG. I&V points ensure that all work is properly performed, that measurements and dimensions are accurately taken and recorded and that all specifications set forth in the drawings and manuals are met.
7-2.2.6 POST-OPERATIONAL PROCEDURES. The operational plan must include post-operational procedures for removing and re-storing equipment, returning personnel to their duty stations and submitting all necessary reports. The NDT inspector assigned to the particular task is responsible for timely submission of all NDT inspection reports.
7-2.2.7 SAFETY PRECAUTIONS. Every NDT task performed underwater will present unique circumstances that can be potentially hazardous to personnel. Each procedural section of this chapter provides specific safety precautions applicable to the task addressed. For direction on general safety precautions refer to Chapter 2 of this manual.
7-2.2.8 CERTIFICATION REQUIREMENTS FOR UWVT. Personnel performing UWVT require certification in UWVT. Certification can only be obtained by training and examination.
7-2.2.8.1 Fleet Examiners. Fleet Examiners certified in conventional VT in accordance with NAVSEA S9086-CH-STM-020 Chapter 074 Volume 2 do not require special certification in underwater visual testing (UWVT) since topside inspection tools, methods and criteria are applied directly to underwater visual inspections. The Fleet Examiner must become familiar with limitations associated with UWVT and conduct training and testing of Fleet Inspectors that addresses these limitations.
7-2.2.8.2 Fleet Inspectors (Divers). Divers will be trained for UWVT by a conventionally certified VT Examiner or Inspector. Training will include all aspects of visual inspection normally required for weld inspection and VT performed in conjunction with MT and UT. This training will include underwater inspections on well characterized test pieces, using VT tools as appropriate. Divers will be certified as Level II Limited Visual Inspectors by the cognizant VT Examiner, based on successful completion of training and both written and practical examinations. Certification will be limited to UWVT performed in accordance with a procedure approved by the cognizant Examiner. Certification will be valid for three years. However, if the technique is not used for a period of six months, proficiency must be demonstrated to the Examiner by successfully inspecting a test piece prior to performing any inspections for acceptance or rejection.
7-2.2.8.3 Non-Fleet Personnel. Employees of the Department of Defense (DoD) seeking certification in UWVT shall adhere to the same requirements as outlined for Fleet personnel, above. Non-DoD activities desiring to utilize UWVT must establish a program similar to that described above, which meets the requirements of MIL-STD-271 for training and certification of inspection personnel.
7-2.2.9 CERTIFICATION REQUIREMENTS FOR UWMT. Personnel performing UWMT require certification in UWMT. Certification can only be obtained by training and examination.
7-2.2.9.1 Fleet Examiners. Examiner candidates for UWMT must hold prior certification as Examiners in conventional MT in accordance with NAVSEA S9086-CH-STM-020 Chapter 074 Volume 2. Training will be provided either at a facility designated by NAVSEA's agent or at the candidate's activity, utilizing divers as part of the training program and including hands-on training with topside tanks. Certification of Examiners in UWMT will be confirmed by notifying the NAVSEA Certification Agency (NDT program coordinator) upon satisfactory completion of an examination administered by NAVSEA's agent. Certification shall be valid for a period of five years, provided that the individual maintains Examiner certification in conventional MT. Recertification shall be accomplished by repeating the requirements for original certification.
7-2.2.9.2 Fleet Inspectors (Divers). Divers may be trained either by a certified UWMT Examiner or by NAVSEA's agent. Training may be accomplished at either the diver's activity or at the agent's facility, as determined by NAVSEA. Regardless of where training was administered and by whom, certification will be by the cognizant UWMT Examiner based on satisfactory completion of both practical and written examinations. Certification will be limited to UWMT using equipment provided by NAVSEA and a procedure approved by NAVSEA. Certification will be valid for three years. However, if the individual does not perform UWMT for a period of six months or more, proficiency must be demonstrated to the cognizant UWMT Examiner by successfully inspecting a test plate prior to performing any inspections for acceptance or rejection.
7-2.2.9.3 Non-fleet Personnel. Employees of the Department of Defense (DoD) seeking certification in UWMT shall adhere to the same requirements as outlined for Fleet personnel above. Non-DoD activities desiring to utilize UWMT must establish a program similar to that described above which meets the requirements of MIL-STD-271 for training and certification of inspection personnel. This program requires NAVSEA approval.
7-2.2.10 CERTIFICATION REQUIREMENTS FOR UWUTG. Personnel performing UWUTG require certification in UWUTG. Certification can only be obtained by training and examination.
7-2.2.10.1 Fleet Examiners. Examiners certified in conventional UT in accordance with NAVSEA S9086-CH-STM-020 Chapter 074 Volume 2 will not require a specific certification in UWUTG, but will be trained in the overall capabilities, limitations and operation of the system and in the use of the available instructional materials. Training will be provided at a facility designated by NAVSEA's agent. Training of Examiners in UWUTG shall be confirmed by notifying the NAVSEA Certification Agency (NDT program coordinator) upon satisfactory completion of the training.
7-2.2.10.2 Fleet Inspectors. Inspector candidates for UWUTG must hold prior certification as Inspectors in conventional ultrasonic thickness testing in accordance with NAVSEA S9086-CH-STM-020 Chapter 074 Volume 2. Training may be administered by NAVSEA's authorized agent or by another person or activity approved by NAVSEA. The training shall consist of a minimum of 40 hours of instruction, using the Inspector's Lecture Guide LG-UWSH-UWUT(I)-1, Diver's Lecture Guide LG-UWSH-UWUT(D)-1 and User's Guide UG-UWSH-UWUT-1 supplied with the Navy UWUTG system. Training will be provided either at a facility designated by NAVSEA's agent or at the candidate's activity, utilizing divers as part of the training program and including hands-on training with topside tanks. In all cases, certification will be by examination (written and practical) and will be issued by the activity's ultrasonic test examiner.
7-2.2.10.3 Non-fleet Personnel. Employees of the Department of Defense (DoD) seeking certification in UWUTG shall adhere to the same requirements as outlined for Fleet personnel above. Non-DoD activities desiring to utilize UWUTG must establish a program similar to that described above which meets the requirements of MIL-STD-271 for training and certification of inspection personnel. This program requires NAVSEA approval.
7-2.2.11 SCHEDULING. Whenever possible, underwater NDT should be scheduled to follow hull cleaning operations to eliminate the time needed by the diver to clean the inspection site(s). This particularly applies to UWUTG because of the large number of individual scanning sites involved.
Chapter 2 of this manual, General Information and Safety Precautions, contains guidelines for preparing for underwater ship husbandry (UWSH) tasks. General preparation requirements for NDT methods are discussed below. Section 3 contains specific requirements for UWVT, UWMT and UWUTG.
7-2.3.1 EQUIPMENT, TOOLS and MATERIALS. The following paragraphs describe the equipment, tools and materials that need to be assembled at the site to perform NDT surface preparation, inspection and recording tasks. While most surface preparation and recording equipment is common to all NDT methods, inspection equipment varies with each method. Inspection equipment specific to each NDT method is discussed under the separate method heads and listed along with general preparation and recording equipment in the tables. Equipment, tools and materials required for specific tasks may vary depending on the area being inspected and its condition.
7-2.3.2 PROTECTIVE EQUIPMENT. During surface preparation where the removal of organotin anti-fouling paints may be necessary, all areas of skin subject to water exposure must be protected. For protection, divers should wear a dry suit with full helmet. If this is not possible, divers should wear a wet suit, full face mask, hood, gloves and bootees. All areas of skin subject to water encroachment must be coated with a water-insoluble cream before donning wet suits, full face masks, hoods, gloves and bootees. Federal Specification PS-411 type III protective cream is recommended. This cream is available under NSN 6850-00-244-4892 in 1-pound jars.
7-2.3.3 DIVER STAGING EQUIPMENT. A staging device, rigged into position directly below the area to be inspected is recommended for use by the diver to remain stable while conducting UWVT and UWMT in specific locations.
7-2.3.4 SURFACE PREPARATION AND RESTORATION EQUIPMENT. NDT operations require inspection surfaces to be prepared by using one or more of the following types of equipment: pneumatic or hydraulic hand-held grinder with abrasive disk or wire brush; high-pressure water jet; or hand-held brushes, pads (greenies) and scrapers. An informative assessment of the material condition of a ship's hull cannot be made if the hull is even moderately fouled. Functional descriptions of surface preparation equipment are provided below:
Hydraulic or Pneumatic Hand-Held Grinder: Divers use the hydraulic or pneumatic hand-held grinder with an abrasive disk or wire brush attachment (figure 7-2-1) to remove marine growth, scale or paint from the surface of the area to be inspected. A small grinder, commonly called a peanut grinder, can be used to remove corrosion prior to inspection or to even the surface area where light surface pitting is found. When removing fouling from painted surfaces, the use of brushes as described in NSTM Chapter 081 is recommended. The grinder requires two-handed operation.
High-Pressure Water Jet: Divers use the water jet (figure 7-2-2) to remove marine growth, scale and paint from the surface of the area to be inspected. It requires two-handed operation. The water jet is best suited for cleaning the rough irregular surfaces of weldments. Divers should not use the jet on painted surfaces that do not require paint removal.
Hand-Held Brushes, Pads (Greenies) and Scrapers: Divers use hand-held cleaning devices during inspection to remove localized marine growth and surface corrosion that can mask surface discontinuities or interfere with UWUTG scanning or UWMT yoke placement. Certain geometric hull configurations, because of restricted access or radical curvature, make proper surface preparation difficult using power tools. When divers cannot use power tools, they must use hand-held cleaning devices.
Anticorrosion Coating: UWMT operations require the diver to apply a suitable underwater coating to the bare metal areas exposed during surface preparation to prevent corrosion. An underwater epoxy approved by NAVSEA 00C5 is required.
Preparation for conducting UWVT entails assembling all necessary material and personnel required to safely satisfy the plan requirements. Divers must determine that the underwater visibility is adequate for the performance of the inspection. The following paragraphs describe inspection equipment required to conduct UWVT by fleet personnel. Table 7-2-1 lists all inspection equipment specific to UWVT, along with general surface preparation and recording equipment. Non-fleet users require similar equipment, but need not comply with the NAVSEAINST 10560.2 listing.
7-2.4.1 UWVT EQUIPMENT. Power Cable: A two-conductor power cable with a braided external ground and a protective jacket (figure 7-2-3), listed in NAVSEAINST 10560.2, delivers power to the white light source. Typical cables are 250 feet long to permit operation in the majority of locations accessible by a surface-supported diver. The external ground braid generates a ground fault whenever the cable is cut; the power conductors cannot be reached except by first penetrating the ground braid.
Appropriate Weld Inspection Gages and Measuring Tools: The tools required will vary with the nature of the inspection (i.e. fit-up, final, damage assessment, etc.).
Ground Fault Interrupter (GFI): The diver's primary protection from electric shock is an approved isolation transformer/GFI device (figure 7-2-4), listed in NAVSEAINST 10560.2. The GFI interrupts power when it senses a drop in the resistance between the isolated system power leg and the power supply ground.
White Light Source: The primary illumination source is a Remote Ocean Systems model TUBE-LIGHT, listed in NAVSEAINST 10560.2.
Preparation for conducting UWMT entails assembling all necessary material and personnel required to safely satisfy the plan requirements. Divers must determine that the water current will not affect the application of magnetic particles where UWMT is to be conducted. Water currents greater than one knot make it difficult to perform UWMT. Divers must also determine that the underwater visibility is adequate for the interpretation of the test results. The following paragraphs describe inspection equipment required to conduct UWMT by fleet personnel. Table 7-2-2 lists all inspection equipment specific to UWMT, along with general surface preparation and recording equipment. Non-fleet users require similar equipment, but need not comply with the NAVSEAINST 10560.2 listing.
7-2.5.1 UWMT EQUIPMENT. Electromagnetic Yoke: An electromagnetic yoke (figure 7-2-5), which meets the specifications of MIL-STD-271 and is listed in NAVSEAINST 10560.2, is used to induce a magnetic field in the material. The articulation of the yoke's legs allow any pole spacing between 2 inches and 8 inches and the yoke can accommodate plate offsets of up to 6 inches and joint angles from about 45 degrees to 270 degrees. To minimize the risk of electric shock, there are no controls on the yoke. A topside operator energizes the yoke.
Power Cable: A two-conductor power cable with a braided external ground and a protective jacket (see figure 7-2-3), listed in NAVSEAINST 10560.2, delivers power to the electromagnetic yoke. Typical cables are 250 feet long to permit operation in the majority of locations accessible by a surface-supported diver. The external ground braid generates a ground fault whenever the cable is cut; the power conductors cannot be reached except by first penetrating the ground braid.
Ground Fault Interrupter (GFI): The diver's primary protection from electric shock is an approved isolation transformer/GFI device (see figure 7-2-4), listed in NAVSEAINST 10560.2. The GFI interrupts power when it senses current leakage between the isolated system power leg and the power supply ground.
White Light Source: The primary illumination source is a Remote Ocean Systems model TUBE-LIGHT, listed in NAVSEAINST 10560.2.
Magnetic Particles: Magnetic particles are finely divided ferromagnetic particles having a low magnetic retentivity and a high permeability. The magnetic particles used for UWMT must meet the specifications of MIL-STD-271. They are dyed pink to be visible under normal lighting. The particles are mixed with wetting agents and corrosion inhibitors to enhance their underwater performance.
Magnetic Particle Applicator: The magnetic particle applicator is a reservoir of magnetic particles and water that the diver uses to deliver magnetic particles to the surface of the inspection area. A simple and effective magnetic particle applicator is a plastic squeeze bottle that contains a marble-sized object to aid in mixing.
Magnetic Field Indicator: The magnetic field indicator is a small device with crack-like discontinuities on its face. The indicator is used to determine if the inspection site has adequate magnetic flux. The diver places the indicator at the inspection site, topside energizes the yoke and the diver delivers the particles. A clearly visible accumulation of particles (indications) should then form along the crack-like discontinuities on the pie-shaped magnetic field indicator (figure 7-2-6). In the pie-shaped gauge, the crack-like discontinuities are furnace-brazed joints between adjacent steel wedges. Though a simple test to measure the magnetic field strength inside the material being inspected is unknown, it is assumed that an adequate field just outside the material signifies an adequate field inside as well.
Preparation for conducting UWUTG entails assembling all necessary materials, equipment and personnel required to safely satisfy the plan requirements, including arranging for any required training for the dive team. The following paragraphs describe the inspection equipment required to conduct UWUTG by fleet personnel. Non-fleet users will require similar equipment, but specific item descriptions may be different and computer-related data acquisition equipment may not be required. Table 7-2-3 lists the inspection equipment specific to UWUTG, along with general surface preparation materials and equipment for recording inspection results.
7-2.6.1 UWUTG EQUIPMENT. Ultrasonic Transducer: The transducer used in UWUTG is a commercially available immersion transducer with a frequency of 1 to 10 megahertz, that is highly damped and designed for high resolution. It has a diameter of approximately 1/2 inch and is about 2 inches long.
Underwater Transducer Housing: The housing for the transducer consists of a machined plastic body with a stainless steel base plate and a stainless steel acoustic mirror. The housing unit protects the transducer from abuse and provides a constant standoff distance between the transducer and the surface of the material being inspected. The housing is about 8 inches by 2 inches.
Calibration Block: The system calibration block is a five-stepped block of material that is acoustically similar to the material of the hulls being tested. The minimum step is approximately 0.15 inches thick and the maximum step is approximately 1 inch thick.
Transducer Cable: The transducer cable is a C-N-4 coax cable, usually 250 feet long. One end has a BNC connector and the other has a waterproof UHF connector that mates with the transducer.
Desktop Computer: The desktop computer is an IBM PC-compatible microcomputer with an analog-to-digital converter installed. The computer collects data, correlates data points, stores pertinent information and provides a printed record of all data.
Ground Fault Interrupter (GFI): The diver's primary protection from electric shock is an approved isolation transformer/GFI device (see figure 7-2-4), listed in NAVSEAINST 10560.2. The GFI interrupts power when it senses current leakage between the isolated system power leg and the power supply ground.
Ultrasonic Instrument: The ultrasonic instrument is a pulse echo device capable of detecting flaws and measuring wall thickness in a variety of materials. The instrument has a CRT and digital readout. The instrument meets the specifications of MIL-STD-271. It is also specially modified by the manufacturer to facilitate communication with the computer.
Premarked Hogging Lines: The hogging lines are marked at regular intervals to provide a location reference. The hogging lines can be two equal lengths that can be connected at the keel or a single length that spans the hull from port to starboard.
The following paragraphs describe equipment useful for recording NDT results. The determination as to whether or not any of this equipment is required for a particular operation is left to the on-site NDT inspector.
Stereo Camera: Stereophotography produces three-dimensional images by using two photographs of the same object taken from two distinct camera positions while lighting and object distance are held constant. Stereo photographs can be used to estimate the depth of corrosion pits, the depth and type of marine growth and depth and width of some surface cracks. Some stereophotographic systems include video cameras operated by topside personnel who view the inspection area through a video monitor and select stereophotos to be taken.
Still Camera: Still photography produces photographs or slides of specific areas, openings and appendages on ships' hulls. The still camera is an individually controlled instrument and requires an experienced photographer to produce quality photographs. Close-up photography is mandatory for documentation and interpretation of indications and damage. Photo documentation is an excellent method of presenting inspection results to a topside NDT inspector for review. Photographs can document work performed during UWMT.
Video System: Video systems include a video camera with enough cable to reach the area to be inspected, a monitor for topside viewing and a recording device. Because a topside NDT inspector can monitor a task in progress on a video system, it is an excellent quality assurance tool. When used in conjunction with a video recorder, it can often serve as a documentation tool.Verbal communications between topside and divers can be recorded with many underwater video systems (i.e., DUCTS) and provide an excellent source of inspection documentation.
Grease Pencil: Standard, highly visible, grease pencils can be used to mark areas with abnormal conditions that may require more detailed inspection.
Measuring Tape: Measuring tapes, preferably cloth with a magnet attached to one end, can be used to record the size and location of abnormalities found during an inspection.
Writing Slate: Tablet-sized plexiglas sheets can be used to record locations and measurements of specific areas. Verbal communications with topside are frequently used instead of writing on an underwater slate.
This section contains general procedures and techniques for three underwater NDT methods: underwater visual testing (UWVT), underwater magnetic particle testing (UWMT) and underwater ultrasonic thickness gauging (UWUTG). The general procedures and techniques apply to these NDT methods and equipment and may be adapted for a specific hull area or appendage. In most cases, underwater NDT requires that locations be determined fairly accurately. Hogging lines are often used to provide the diver with a reference location. In many cases, hogging lines or other reference markers may already be in place in association with some other underwater activity. Since each siutation is different, it will be necessary to determine if location acceptance is required for a specific NDT operation. This section also includes surface preparation requirements that are unique to each method.
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When divers are performing underwater NDT, they should also be observing the general condition of the hull and other components for signs of damage or deterioration. Any such observations should be reported to topside personnel.
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This section provides general recommendations for performing UWVT. It can be used as a guide for the preparation of the written procedure required by MIL-STD-271 (see 7-2.2.4). A check-list of inspection and verification (I&V) points should be developed from the procedure for each job.
7-3.2.1 HULL SURFACE PREPARATION. Hull surface preparation for UWVT will generally be controlled by the associated welding or inspection procedure. For example, when UWVT is used to determine the suitability of a surface for UWMT, the surface must be bare metal in an area which includes the suspect region or weld and an area 1/2" on all sides around this region. When UWVT is used to determine the suitability of a surface for UWUTG, it is only necessary to remove marine growth; paint may be left intact. For close visual inspection to discover such discontinuities as cracking or undercut, all marine growth, paint and oxidation products must be removed. It is the inspector's responsibility to ensure that relevant indications will not be masked by inadequate surface preparation.
7-3.2.2 UWVT PROCESS.
7-3.2.2.1 Before starting the underwater visual inspection, the diver must be briefed on specific inspection tasks to be accomplished, the frequency of measurements to be taken, recording and reporting requirements, etc. All tools should be checked for the visibility of markings, the diver's faceplate checked for clarity and cleanliness and the proper functioning of communications verified.
7-3.2.2.2 Upon arrival at the inspection site, the diver should check lighting and other environmental conditions to ensure that reliable results can be achieved.
7-3.2.2.3 Visual inspection should proceed according to a written plan, with inspection and verification (I&V) points noted topside. Communications between the diver and topside should be used freely to step the diver through required observations and measurements. Where video documentation is used, a running commentary should be logged describing the area being inspection and its condition.
7-3.2.2.4 Upon completion of each UWVT dive, all measurement tools should be cleaned and protected against corrosion.
7-3.2.2.5 If bare metal was exposed as part of the inspection procedure, it must be recoated. Prepare the epoxy anticorrosion coating topside for application to the bare metal area. Use a hand-held wire brush to roughen the painted area surrounding the bare metal area for a distance of three to five inches. Apply the epoxy coating to cover the bare metal and the roughened paint edges, tapering the edges to blend smoothly into the paint (I&V).
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7-3.2.2.6 Inspection reports should contain, as a minimum, the entire QA package, as well as the sizes and locations of all indications detected, including any sketches, photographs or video-tapes produced during the inspection. If repairs to discontinuities were performed, the reinspection data associated with the repairs should also be included.
This section provides general recommendations for performing UWMT. The section can be used as a guide for the preparation of the written procedure required by MIL-STD-271 (see 7-2.2.4). Some of the steps in the following paragraphs are designated as I&V points that should appear in the UWMT QA Package developed for each UWMT operation (appendix A). The equipment described in Table 7-2-2 should be assembled at the UWMT site.
7-3.3.1 HULL SURFACE PREPARATION
7-3.3.1.1 Position a diving stage immediately below the area to be inspected. Secure the diving stage allowing enough distance from the surface of the area to be inspected for the diver to work comfortably. Because of the amount of equipment the diver must handle simultaneously (i.e., yoke, particle bottle, pie gauge, light) a stage is strongly recommended. This allows the diver to concentrate on the inspection details.
7-3.3.1.2 Remove all marine growth, corrosion and paint from the surface of the area to be inspected (figure 7-3-1) (I&V).
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7-3.3.1.3 Visually inspect the bare metal area for any residual marine growth, corrosion or paint which, if not removed, can result in false indications of discontinuities (I&V).
7-3.3.2 UWMT PROCESS
7-3.3.2.1 Transfer the electromagnetic yoke, the particle applicator containing the particle slurry and the magnetic field indicator to the diver.
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7-3.3.2.2 Position the electromagnetic yoke against the surface of the area to be inspected. Ensure that the legs of the yoke straddle the area to be inspected and that the base of the legs have full contact with the cleaned area of the hull surface (figure 7-3-2) (I&V). Also ensure that the legs spacing does not exceed eight inches. Energize the yoke.
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7-3.3.2.3 Place a magnetic field indicator against the inspection surface between the legs of the yoke (figure 7-3-3). Squeeze a slurry of magnetic particles into the area between the legs of the magnetic yoke (figure 7-3-4).
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7-3.3.2.4 Observe the field indicator's response. A positive indication (accumulation of particles) should be seen along the crack-like discontinuities (figure 7-3-5) (I&V). This indicates that the UWMT system is operating properly.
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7-3.3.2.5 Remove the field indicator from the inspection surface.
7-3.3.2.6 Brush gently by hand to remove any residual particles from the inspection area. Apply a fresh slurry of particles into the area between the legs of the yoke. Without rubbing the surface, gently fan away, by hand, any residual particles from the surface area between the yoke legs and visually inspect the area for particle accumulations (indications).
7-3.3.2.7 If no indications are found, brush gently by hand to remove any residual particles from the inspection area, move the yoke to the next inspection position (figure 7-3-6) and reapply fresh slurry.
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7-3.3.2.8 If an indication is detected, keep the yoke positioned at 90 degrees (perpendicular) to the indication and continue moving the yoke and retesting until the ends of the suspected discontinuity are located.
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Record the position and length of the indication by any suitable means (sketch, video camera, still camera, etc.) (I&V). Permanently mark the ends of the indication using an arrow punch or similar device (figure 7-3-7).
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7-3.3.2.9 Validate the UWMT inspections by using the magnetic field indicator to confirm the system operation as described in 7-3.3.2.3 and 7-3.3.2.4.
7-3.3.2.10 Prepare the epoxy anticorrosion coating topside for application to the bare metal area. Use a hand-held wire brush to remove all residual magnetic particles from the bare metal surface and to roughen the painted area surrounding the bare metal area for a distance of three to five inches. Apply the epoxy coating to cover the bare metal and the roughened paint edges, tapering the edges to blend smoothly into the paint (I&V).
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7-3.3.2.11 Inspection reports should contain, as a minimum, the entire QA package, as well as the sizes and locations of all indications detected, including any sketches, photographs or videotapes produced during the inspection. If repairs to discontinuities were performed, the reinspection data associated with the repairs should also be included.
This section provides general recommendations for performing UWUTG. The section can be used as a guide for the preparation of the written procedure required by MIL-STD-271 (see 7-2.2.4). Some of the steps in the following paragraphs are designated as I&V points that should appear in the UWUTG QA package developed for each UWUTG operation (appendix B). The equipment described in Table 7-2-3 should be assembled at the UWUTG site.
7-3.4.1 HULL SURFACE PREPARATION Since UWUTG is conducted over such a large expanse of the hull, the surface preparation steps have been incorporated into the actual UWUTG operation, as described in the following paragraphs.
7-3.4.2 UWUTG PROCESS
7-3.4.2.1 The topside NDT Inspector and the diver who will be manipulating the underwater transducer ensure that the UWUTG system is properly calibrated.
7-3.4.2.2 Topside personnel and diver determine need for positioning equipment (such as hogging lines) and install if necessary.
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7-3.4.2.3 Diver locates the predetermined inspection starting point and visually inspects the surface area for marine growth. If necessary, diver removes marine growth with hand-held scraper to expose an area large enough to perform the required inspection scan.
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7-3.4.2.4 Diver places the ultrasonic transducer against the surface of the area to be inspected and scans the area as directed by the topside NDT Inspector.
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7-3.4.2.5 Diver continues to move hogging lines (if required) and perform UWUTG to cover all areas specified in the operational plan.
7-3.4.2.6 The topside NDT Inspector and the diver ensure that the UWUTG system is still properly calibrated.
7-3.4.2.7 Inspection reports should contain, as a minimum, the entire QA package; a summary report listing any thin areas detected, including their location and surrounding hull condition; and the computer generated raw data.