**Process Specification for Eddy Current Inspection**

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| **Engineering Directorate**                                           |
|                                                                       |
| **Structural Engineering Division**                                   |
|                                                                       |
| **May 2008**                                                          |
|                                                                       |
| ![](media/image1.png)                                                 |
|                                                                       |
| National Aeronautics and                                              |
|                                                                       |
| Space Administration                                                  |
|                                                                       |
| **Lyndon B. Johnson Space Center**                                    |
|                                                                       |
| Houston, Texas                                                        |
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**Process Specification for Eddy Current Inspection**

+--------------------+-----------------------------+-----+-----------+
| **Prepared by:**   | ####                        |     | ***05     |
|                    |                             |     | /14/08*** |
+--------------------+-----------------------------+-----+-----------+
|                    | Ajay Koshti                 |     | Date      |
|                    |                             |     |           |
|                    | Materials and Processes     |     |           |
|                    | Branch/ES4                  |     |           |
+--------------------+-----------------------------+-----+-----------+
|                    |                             |     |           |
+--------------------+-----------------------------+-----+-----------+
|                    |                             |     |           |
+--------------------+-----------------------------+-----+-----------+

+--------------------+-----------------------------+-----+-----------+
| **Reviewed by:**   | ####                        |     | ***05     |
|                    |                             |     | /14/08*** |
+--------------------+-----------------------------+-----+-----------+
|                    | Norman Ruffino,             |     | Date      |
|                    |                             |     |           |
|                    | Materials and Processes     |     |           |
|                    | Branch/ES44 (ESCG)          |     |           |
+--------------------+-----------------------------+-----+-----------+
|                    |                             |     |           |
+--------------------+-----------------------------+-----+-----------+
| **Reviewed by:**   | ####                        |     | ***05     |
|                    |                             |     | /14/08*** |
+--------------------+-----------------------------+-----+-----------+
|                    | David Stanley,              |     | Date      |
|                    |                             |     |           |
|                    | Materials and Processes     |     |           |
|                    | Branch/ES4 (ESCG)           |     |           |
+--------------------+-----------------------------+-----+-----------+
|                    |                             |     |           |
+--------------------+-----------------------------+-----+-----------+

+--------------------+-----------------------------+-----+-----------+
| **Approved by:**   | ####                        |     | ***05     |
|                    |                             |     | /14/08*** |
+--------------------+-----------------------------+-----+-----------+
|                    | Bradley S. Files,           |     | Date      |
|                    |                             |     |           |
|                    | Chief, Materials and        |     |           |
|                    | Processes Branch/ES4        |     |           |
+--------------------+-----------------------------+-----+-----------+

+---------+--------------------------------------------+--------------+
| RE      |                                            |              |
| VISIONS |                                            |              |
+---------+--------------------------------------------+--------------+
| VERSION | CHANGES                                    | DATE         |
+---------+--------------------------------------------+--------------+
| \--     | Original version                           | 12/1/00      |
+---------+--------------------------------------------+--------------+
| A       | Reviewed document per QMS requirements.    | 04/22/04     |
|         | Updated division name, organization codes, |              |
|         | and document numbers.                      |              |
+---------+--------------------------------------------+--------------+
| B       | Added new NDE calibration notch classes    | 05/01/08     |
|         | and NDE standards. Added applicability to  |              |
|         | inspection of bolts.                       |              |
|         |                                            |              |
|         | Defined standard NDE and special NDE in    |              |
|         | terms of calibration notch size and crack  |              |
|         | detectability                              |              |
+---------+--------------------------------------------+--------------+
|         |                                            |              |
+---------+--------------------------------------------+--------------+

**1.0 [SCOPE]{.underline}**

This process specification establishes the minimum requirements for eddy
current inspection of flat surfaces, fastener holes, threaded fasteners
and seamless and welded tubular products made from nonmagnetic alloys
such as aluminum and stainless steel.

# **2.0 APPLICABILITY**

This specification is primarily applicable to in-process, final, and
in-service eddy current inspections to detect surface and near surface
cracks and crack-like flaws. However, usage is not limited to those
applications.

**2.1 FLAT SURFACES**

This specification is applicable to the inspection of relatively flat
surfaces with a surface finish of 125 μin. or better. This process shall
be used for directed inspections of critical or damaged areas. It shall
not be used for global inspection of areas greater than 2 sq. ft. unless
automated scanning equipment is used.

**2.2 FASTENER HOLES**

This specification is applicable to the inspection of open fastener
holes with an interior surface finish of 125 μin. or better using a
rotating hole scanner or a manual bolt hole probe.

3.  **THREADED FASTENERS**

This specification is applicable to the inspection of root of fastener
threads, shank surface, shank neck down region and fillet radius under
the bolt head with surface finish of 125 μin. or better and fillet
radius of 1/32 in. or greater.

**2.4 TUBULAR PRODUCTS**

This specification is applicable to the inspection of both seamless and
welded tubular products using either an encircling or probe coil
technique. The use of ID probe techniques is not covered by this
specification. This specification covers the inspection of tubular
products ranging in diameter from 0.125 to 5 in. with wall thicknesses
ranging from 0.005 to 0.250 in.

**3.0 [USAGE]{.underline}**

This specification shall be invoked by an inspection callout on the
engineering drawing or by a reference in a Process Specification, Task
Performance Sheet, Discrepancy Report/Material Review Record, or other
appropriate document. The engineering drawing or referencing document
shall identify the specific part features or areas that require
inspection. Typical eddy current inspection callouts are as follows:

**EDDY CURRENT INSPECT ALL HOLES PER NASA/JSC PRC-6509 TO STANDARD LEVEL
NDE**

When fracture control requirements necessitate Special Nondestructive
Evaluation (NDE) of a fracture critical component, the requirement for
Special NDE shall appear in the inspection note as shown below. When
Special NDE is required, the specific inspection procedure and inspector
shall be qualified in accordance with Section 6.0.

**EDDY CURRENT INSPECT AREA SHOWN PER NASA/JSC PRC-6509 TO SPECIAL LEVEL
NDE. SPECIAL NDE CERTIFICATION REQUIRED.**

**3.1 INSPECTION SEQUENCE**

The stage in the manufacturing process where inspection is performed
should be specified on the engineering drawing or in the referencing
document.

**3.2 ACCEPTANCE CRITERIA**

Any indication greater than 50 percent of the reference notch response
shall be cause for rejection. For fracture critical parts, questionable
or relevant indications or indications that meet the noise ratio
requirements per 5.5.4.4 and have less than 50 percent of the reference
notch response shall be reported to the responsible engineering
organization for disposition.

**4.0 [REFERENCES]{.underline}**

The following specifications, standards, and handbooks form a part of
this document to the extent specified herein. All documents listed are
assumed to be the current revision unless a specific revision is listed.
In case of conflict between this specification and the technical
requirements cited in other referenced documents, the requirements of
this document take precedence.

ASTM E 426 *Standard Practice for Electromagnetic (Eddy Current)
Examination of Seamless and Welded Tubular Products, Austenitic
Stainless Steel and Similar Alloys*

NASA-STD-5009 *Nondestructive evaluation requirements for Fracture
Critical Metallic Components*

NAS 410 *NAS Certification & Qualification of Nondestructive*

*Test Personnel*

NASA --STD-5019 *Fracture Control Requirements for Spaceflight Hardware*

PRC-5010 *Process Specification for Pickling, Etching, and Descaling of
Metals*

SAE ARP4402 *Eddy Current Inspection of Open Fastener Holes in Aluminum
Aircraft Structure*

SAE AS4787 *Eddy Current Inspection of Circular Holes in Nonferrous
Metallic Aircraft Engine Hardware*

The following references were used to develop this process
specification:

JSC 8500C *Engineering Drawing System Requirements*

SOP-007.1 *Preparation and Revision of Process Specifications*

SAE ARP K99-AA *Eddy Current Surface Crack Detection in Aerospace
Structures (Draft document prepared by SAE AMS Committee K,
Nondestructive Methods and Processes)*

**5.0 [PROCESS REQUIREMENTS]{.underline}**

**5.1 GENERAL**

Eddy Current inspection of flat surfaces, including surfaces around
fastener holes, shall be performed in accordance with this
specification. Fastener holes in aluminum parts shall be inspected in
accordance with ARP4402 and in other alloys in accordance with AS4787
except as modified by this specification. Inspection of tubular products
shall be performed in accordance with ASTM E 426 except as modified by
this specification.

**5.2 WRITTEN PROCEDURES**

A written inspection procedure shall be used for inspection of each
part. The procedure shall meet the requirements of this specification
and shall ensure the consistency and reproducibility of the inspection
at the required sensitivity level. General procedures covering a variety
of different parts may be used provided they meet the requirements of
this specification and clearly apply to the parts to be inspected. When
general procedures are used, a written part specific technique shall be
prepared. Each procedure and technique shall be approved by a Level III
inspector or by a cognizant NDE engineer.

At a minimum, the part specific procedure or the general procedure and
part specific technique shall include the following:

-   The applicable part name and number

-   A description of the part, area of the part, or hole configuration
    to be inspected

-   The alloy type and conductivity

-   The potential defect location and orientation, if known

-   The required eddy current instrument, probes, and fixturing
    equipment including the manufacturer and model numbers

-   The required calibration standard and its conductivity

-   The test frequency

-   Part cleaning and preparation instructions

-   Equipment setup, calibration, and operation procedures

-   Scan plan

-   Procedure for evaluation of questionable indications

A copy of the inspection procedure shall be provided to the responsible
organization upon request.

**5.3 SCAN PLAN**

Unless otherwise specified on the engineering drawing or in the
referencing document, scan plans shall be designed to detect
discontinuities in all credible orientations.

**5.4 REPORTS**

An inspection report shall be prepared for each part or group of parts.
The report shall indicate compliance with this specification, reference
the appropriate written procedure and include the names of personnel
performing the inspection. The report shall identify each part by part
number and serial number and indicate whether each part was accepted or
rejected. The locations and estimated sizes of all reportable flaws
shall be noted in the inspection report. A JSC Form 2176, "Discrepancy
Report/Material Review Record" may be used in place of an inspection
report provided it contains all of the required information. Inspection
reports shall be retained as a permanent quality record and a copy
provided to the responsible design authority.

**5.5 SURFACE INSPECTION**

**5.5.1 EQUIPMENT**

Instrument/probe combinations shall be capable of meeting the
calibration requirements of Section 5.5.4.

**5.5.1.1 INSTRUMENTS**

Instruments shall be equipped with impedance plane, or time base signal
display. Instruments shall be capable of operating between 100 kHz and
6.0 MHz. However, instruments may be operated at other frequencies if
the requirements of Section 5.5.4 are met. Instruments shall be equipped
with an audible and/or visual alarm system. For other than
battery-powered instruments, a voltage regulator shall be used if
instrument internal voltage regulators are not adequate to prevent a
signal variation of 20% or more.

**5.5.1.2 PROBES**

The recommended frequency range for aluminum alloys is 100-500 kHz and
for inconel, CRES and titanium alloys the recommended frequency range is
800 kHz- 3.5 MHz.

Probes shall be marked with their operating frequency or frequency
range. Recommended maximum coil diameter is 0.125 in. The impedance of
probes and adapters shall match the instrument being used. Probes may
have an absolute or differential coil arrangement and may be shielded or
unshielded. However, differential probes shall be oriented (scanned)
normal to the crack direction. Probes shall not give interfering
responses from handling pressure or manipulation and meet the noise
ratio requirements. Probe collars may be used to aid in reducing
lift-off effects. When inspecting for cracks in concave surfaces, the
probe tip shall be convex and shall nest in the radius with less than
.005 in. lift-off.

Non-conductive tape may be applied over the probe coil to protect the
probe from wear. If tape is used, calibration shall be accomplished
after initial application and anytime it is replaced. Use of tape shall
not violate the noise ratio requirements.

**5.5.1.3 SCANNERS**

Automated scanning systems may be used to obtain controlled indexing
between scans. If an automated scanner is used, the calibration
procedure shall include scanning of the reference standard to verify
that the appropriate sensitivity level and noise ratio requirements are
achieved.

4.  **REFERENCE STANDARDS**

Reference standards are based on classes of EDM flaws provided in Table
1.

Table 1: EDM Notch Dimensions in NDE Standards

![](media/image2.wmf){width="5.68125in" height="2.4180555555555556in"}

Table 2 provides a listing of common reference standards. EDM notches in
other standards shall be classified per Table 1. An EDM class
designation implies that the reference EDM size is same as or smaller
than the EDM class size given in the Table 1. Figures 1 - 5 provide
schematics of some of the applicable reference standards. In addition,
the AF standards (7947479 series) are also applicable. The dimensions of
the reference standard, including notch dimensions, shall be measured
and documented. Reference standards shall be certified when required by
the responsible engineering organization.

For non-ferromagnetic materials, the conductivity of the reference
standard shall be no greater than 2 and no less than 2/3 times the
conductivity of the material to be inspected. When the part to be
inspected has a coating, a shim or coating with the same conductivity
(±5% IACS) and thickness (+0.003" -0.000") of the coating on the part
shall be placed over the reference standard during instrument
calibration.

Table 2: List of Applicable Eddy Current Crack Detection Standards

  ------------------- --------------------- ---------------------------------
  Part \#             Material              Description

  7947479-6AL4V-10    6AL-4V Titanium       Air Force General Purpose Eddy
                                            Current Standard

  7947479-304-10      304 Stainless Steel   Air Force General Purpose Eddy
                                            Current Standard

  7947479-7075T6-10   7075-T6 Aluminum      Air Force General Purpose Eddy
                                            Current Standard

                                            

  NEC-6365-2024T8     2024-T3 Alum, 30.08%  Surface Notch Standard
                      IACS                  

  NEC-6365-2024T8     2024-T8 Alum, 40.4%   Surface Notch Standard
                      IACS                  

  NEC-6366-2024T8     2024-T8 Alum, 40.37%  Corner Notch Standard
                      IACS                  

  NEC-6366-2024T3     2024-T3 Alum, 29.65%  Corner Notch Standard
                      IACS                  

  NEC-6367-2024T8     2024-T8 Alum, 40.64%  Long Notch standard
                      IACS                  

  NEC-6367-2024T3     2024-T3 Alum, 29.55%  Long Notch standard
                      IACS                  

  NEC-6368-2024T3     2024-T3 Alum, 29.92%  Thru Notch standard
                      IACS                  

  NEC-6368-2024T8     2024-T8 Alum, 39.98%  Thru Notch standard
                      IACS                  

                                            

  NEC-6365-718        Inconel 718, 1.43     Surface Notch standard
                      %IACS                 

  NEC-6365-304        CRES 304, 2.52 %IACS  Surface Notch standard

  NEC-6365-6Al-4V     6Al-4V, 1.05 %IACS    Surface Notch standard

                                            

  NEC-6367-718        Inconel 718, 1.44     Long Notch standard
                      %IACS                 

  NEC-6367-304        CRES 304, 2.45 %IACS  Long Notch standard

  NEC-6367-6Al-4V     6Al-4V, 1.04 %IACS    Long Notch standard

                                            

  NEC-6366-718        Inconel 718, 1.43     Corner Notch standard
                      %IACS                 

  NEC-6366-304        CRES 304, 2.52 %IACS  Corner Notch standard

  NEC-6366-6Al-4V     6Al-4V, 1.04 %IACS    Corner Notch standard

                                            

  NEC-6368-718        Inconel 718, 1.26     Thru Notch standard
                      %IACS                 

  NEC-6368-304        CRES 304, 1.83 %IACS  Thru Notch standard

  NEC-6368-6Al-4V     6Al-4V, 0.98 %IACS    Thru Notch standard
  ------------------- --------------------- ---------------------------------

Note: The above standards can be procured from Olympus NDT. Equivalent
standards are acceptable.

![](media/image3.wmf){width="5.997916666666667in"
height="2.220138888888889in"}

Figure 1: Surface Notch Calibration Standard

![](media/image4.wmf){width="5.995833333333334in"
height="2.0458333333333334in"}Figure 2: Corner Notch Calibration
Standard

![](media/image5.wmf){width="5.986111111111111in"
height="2.0284722222222222in"}

Figure 3: Long Notch Calibration Standard

![](media/image6.wmf){width="5.9944444444444445in"
height="2.254166666666667in"}

Figure 4: Through Notch Standard

![](media/image7.wmf){width="5.990972222222222in"
height="1.7430555555555556in"}

Note: Notch dimensions are in accordance with the applicable Surface
Notch Class in Table 1.

Figure 5: Bolt Surface Notch Standard (Notch 3 and 4 at Thread Root)

**5.5.1.5 RECORDING DEVICES**

Recording devices, when used, shall be compatible with the instrument
and be capable of generating a permanent record or copy of the signal
response.

**5.5.2 PART PREPARATION**

Dirt, grease, and/or loose paint shall be cleaned from the inspection
surface. If necessary, determine the thickness of any coating with a
coating thickness gage. A similar type and thickness shim or coating
shall be placed over the reference standard for calibration (refer to
Section 5.5.1.4).

**5.5.3 LOCATION OF INSPECTION EQUIPMENT**

Inspection equipment shall be located at least 10 ft. from any items
that generate a large magnetic field, such as motors, generators, or
transformers.

**5.5.4 CALIBRATION, SCANNING AND ACCEPT/REJECT**

**5.5.4.1 GENERAL**

Inspection equipment shall be calibrated against the appropriate
reference standard as specified in Section 5.5.1.4. Evaluation of flaw
indications shall be accomplished by using a
signal-versus-EDM-notch-size curve obtained on the reference standard
notches.

**5.5.4.2 INTERVALS**

Calibration shall be performed at the beginning and conclusion of each
inspection operation and at least every four hours in between.
Calibration shall also be performed if equipment is changed or replaced.
If the response from the reference standard notch has changed by more
than 5% of full scale from the original calibration, perform one of the
following:

1.  If the notch response is greater than that obtained during the
    original calibration, recalibrate and re-inspect any part which was
    rejected since the last calibration.

2.  If the notch response is less than that obtained during the original
    calibration, recalibrate and re-inspect all parts inspected since
    the last calibration.

**5.5.4.3 CRACK ORIENTATION AND PROBE LIMITATIONS**

Cracks are assumed to be oriented in the following directions.

For internal corner edges, cracks may run along the corner or across the
fillet radius (\>1/16"). Compound internal corners (1/8" wide region)
with radius less than 1/8" can not be inspected by eddy current. 1/8" OD
pencil probes recommended.

In bolt threads, cracks are assumed to run along the thread root in the
helical/circumferential direction. For bolt shank, the cracks may run in
the axial or circumferential direction. On bolt neck down areas (radius
\> 1/16") and in corners (radius \> 1/16") under bolt heads, cracks are
assumed to run in a circumferential direction. Zones at the thread
termination on the shank side can not be inspected by a nut probe or
V-probe if a thread relief zone is not provided. Special NDE inspection
is not performed on the threaded fasteners due to lack of threaded crack
specimens.

On external edges, the crack is assumed to run normal to the edge.
Compound external corners (1/8" wide region) with radius less than 1/8"
can not be inspected.

For bolt holes, the cracks are assumed to run axially.

Cracks caused by the fatigue or static load are assumed to appear across
the direction of principal stress at the location of interest. Eddy
current assumes that the cracks are scanned in a direction +/- 45 degree
normal to the crack at an indexing width of ½ the probe coil diameter

4.  **NOISE RATIO REQUIREMENTS**

Inspection sensitivities for scanning and evaluation are different.
However, the reject level setting is the same during part scanning and
indication evaluation. The reject level is set to 50% of vertical
response from the calibration notch. The ratio of the reject level to
the observed noise, called the noise ratio, shall be visually assessed
during calibration, scanning and evaluation. During the calibration on
the reference EDM notch and during evaluation of an indication, the
ratio shall be 3:1 or greater. During part scanning, the noise ratio
shall be 2:1 or greater.

**5.5.4.5** **SENSITIVITY LEVELS AND NOTCH CLASSES**

General: Sensitivity level is achieved by use of an appropriate
calibration EDM notch and meeting other requirements provided here. The
calibration notches are classified by size as A2 , A3, A4 and A5. Lower
notch class designations (e.g. A3) use a smaller calibration EDM notch
compared to the higher notch class (e.g. A4). Each calibration notch
class defines a primary reference notch as the surface notch and a
secondary reference notch as the corner notch. The secondary notch is
applicable for inspection of bolt holes and external corners. Notch
Class A3 sensitivity level is considered to be the default level
Standard level NDE. Use Table 3 in selection of the notch class if the
notch class is not provided in the callout of eddy current inspection on
the work authorizing document.

An example of notch class A4 sensitivity level is provided below. Use
the surface notch A4 for surface inspection and fillet radius. For
inspecting external corners, use the secondary notch (e.g. A4) with the
same class designation. For inspecting edge of webs (0.1" thick) use the
corresponding edge/through notch (e.g. T4) with matching numeral or
select the edge notch based on comparison of eddy current signal
amplitude from the edge notch to the eddy current response from the
primary Notch A4. A long notch (e.g. L4) may be selected for calibration
based on comparison of eddy current signal amplitude from the long notch
to the eddy current response from the primary notch.

The reject level shall be 50% of the reference notch amplitude. When
establishing the system sensitivity, the reference standard shall be
scanned at the same speed that will be used on the part to be inspected.
During scanning the gain shall be set to 4-6 dB higher than during
calibration without changing the reject level. If the alarm is used, the
alarm level shall be less than or equal to the reject level. Once an
indication is detected the gain shall be lowered to the original
calibration gain in order to evaluate the indication by rescanning to
optimize the indication height.

Ratio of crack length to EDM length providing the same eddy current
amplitude is assumed to be between 1.5 to 2 for class A3 with optimum
eddy current set-up. Crack detectability for class A3 calibration can be
as small as the size of the EDM notch upon POD demonstration. Follow
recommendation of Table 3 for crack detectability size.

Standard NDE: Standard NDE Sensitivity Level is established by using the
primary surface calibration notch A3, A4 or A5. This notch is applicable
for inspection of root of threads, bolt neck down areas, shanks, and
fillet radius. Standard NDE crack size is 0.100" long x 0.050" deep
surface crack or 0.075" long x 0.075" long corner crack.

Special NDE: Special NDE sensitivity Levels shall have class levels A2,
A3 and A4. A correlation between the EDM notch size and the crack size
providing same signal amplitude is required. Moreover, a 90/95 point
estimate demonstration of the eddy current technique on real crack
specimens with the desired crack size is required. Successful
demonstration is necessary to qualify the eddy current operator and the
procedure. Upon qualification of the operator and the procedure, a
Special NDE certificate is issued to the operator by NASA NDE. Special
level eddy current can be performed only by a currently certified
special level eddy current operator. Typical Special NDE crack size is
0.050" long x 0.025" deep surface crack or 0.035" long x 0.035" long
corner crack. Special NDE requirements are applicable for crack
detectability of size smaller than 0.075" long x 0.037" deep,

Table 3: Sensitivity and Class of Calibration Notch

+-------------------------+------+-------------------------------------+
| Sensitivity             | N    | Comment                             |
|                         | otch |                                     |
|                         | C    |                                     |
|                         | lass |                                     |
+-------------------------+------+-------------------------------------+
| Standard                | A3   | Default class. Smaller Crack        |
|                         |      | detectability size (≥ 0.075" long x |
| (Crack detectability:   |      | 0.037" deep) with POD               |
| 0.1'' long X 0.050"     |      | documentation\* on similar          |
| deep crack)             |      | technique and material              |
+-------------------------+------+-------------------------------------+
| Standard                | A4   | Use if A3 not feasible or not       |
|                         |      | needed.                             |
| (Crack detectability:   |      |                                     |
| 0.1'' long X 0.050"     |      | Smaller Crack detectability size (≥ |
| deep crack)             |      | 0.075" long x 0.037" deep) with POD |
|                         |      | documentation\* on similar          |
|                         |      | technique and material              |
+-------------------------+------+-------------------------------------+
| Standard                | A5   | Use if A4 not feasible or not       |
|                         |      | needed.                             |
| (Crack detectability:   |      |                                     |
| 0.1'' long X 0.050"     |      | Smaller Crack detectability size (≥ |
| deep crack)             |      | 0.075" long x 0.037" deep) with POD |
|                         |      | documentation\* on similar          |
|                         |      | technique and material              |
+-------------------------+------+-------------------------------------+
|                         |      |                                     |
+-------------------------+------+-------------------------------------+
| Special NDE (0.050"     | A2   | Need POD Demonstration and          |
| long X 0.025" deep      |      | Certification, Smaller Crack        |
| crack)                  |      | detectability size (≥ 0.030" long x |
|                         |      | 0.015" deep) possible               |
+-------------------------+------+-------------------------------------+
| Special NDE (Crack      | A3   | Default class, Need POD             |
| detectability: 0.050"   |      | Demonstration and Certification     |
| long X 0.025" deep      |      |                                     |
| crack)                  |      |                                     |
+-------------------------+------+-------------------------------------+
| Special NDE (Crack      | A4   | Need POD Demonstration and          |
| detectability: 0.050"   |      | Certification                       |
| long X 0.025" deep      |      |                                     |
| crack)                  |      |                                     |
+-------------------------+------+-------------------------------------+
| \* - The POD            |      |                                     |
| documentation shall     |      |                                     |
| constitute a POD study  |      |                                     |
| on fatigue cracks       |      |                                     |
| providing the 90/95     |      |                                     |
| crack size equal to or  |      |                                     |
| smaller than 0.075"     |      |                                     |
| long x 0.0.37" deep     |      |                                     |
| using a calibration     |      |                                     |
| notch with the desired  |      |                                     |
| class.                  |      |                                     |
+-------------------------+------+-------------------------------------+

**5.5.4.6 SCANNING**

The probe shall be scanned on the reference notch in the same relative
direction as the expected direction of the crack. Reject level is
established as the 50% of the signal height from the reference notch.
This is called the calibration set-up. Part scanning sensitivity shall
be set by adding 4-6 dB gain to the calibration set-up vertical
component In addition, it is also recommended to add 4-6 dB to the
calibaration set-up to establish scanning sensitivity. This set-up is
called the scanning set-up. If expected direction of crack is not known,
the scan shall be performed in two orthogonal directions, unless the
instrument settings are set to detect cracks oriented in the most
unfavorable direction with respect to the scanning direction. The
scanning index for both manual and automated scans shall not exceed
one-half of the effective probe coil diameter. For shielded probes the
effective probe coil diameter shall be equal to probe O.D.

For unshielded probes, the effective probe coil width is based on eddy
current scans of the calibration notch. Perform several closely spaced
parallel scans of the calibration flaw and mark locations of the maximum
signal scan line and 50% of the maximum signal scan lines on each side
of the maximum signal scan line. The distance between the two 50% scan
lines is a measure of the effective probe coil diameter.

For manual scans, a nonconductive probe guide or template shall be used
to ensure that the required scan index is achieved. Scan plans shall be
designed to detect discontinuities in all credible orientations.

**5.5.6 INTERPRETATION OF INDICATIONS**

The presence of a potential crack is indicated by a rapid signal
response similar in appearance to the reference notch response. Once an
indication is detected during scanning, it shall be evaluated using the
calibration set-up. The indication area is carefully rescanned using the
calibration set-up to optimize (maximize) the indication height by
finding the most favorable scan direction and location. Compare the
optimum crack response to the optimum reference notch response. A
response amplitude greater than 50% of the reference notch response
indicates the presence of a crack. Questionable indications or
indications showing less than 50% of the reference notch response may
indicate a defect condition. The following steps should be taken to
evaluate the significance of such indications:

1.  Non-conductive coatings may reduce the amplitude of the crack
    signal. Assess coating thickness and compensate for the coating
    thickness.

2.  Smeared metal on the surface of the part may reduce the amplitude of
    the crack signal. Etch the part per PRC-5010, section 6.3.2 "Etching
    for Penetrant Inspection", re-calibrate, and re-inspect.

3.  If the defect condition is at an edge, use an edge guide with the
    slotted reference standard and re-calibrate. Using the edge guide,
    re-inspect the part.

**6.0 [SPECIAL NDE QUALIFICATION]{.underline}**

Use of Special NDE in accordance with NASA-STD-5009 requires formal
demonstration of the capability to detect Cracks at least as small as
the critical initial crack size for the specific component to a 90/95
probability of detection level. Each procedure, procedure application,
and operator must demonstrate the required capability. Requests for
Special NDE qualification shall be directed to the JSC Materials and
Processes Branch (ES4).

## **7.0 [DEVIATIONS AND WAIVERS]{.underline}**

Any deviations or waivers regarding the use of this process
specification shall be requested in writing. This request shall be
directed to the JSC Materials and Processes Branch (ES4) with the
appropriate justification and rationale. A written response will be
provided upon such a request.

**8.0 [TRAINING AND CERTIFICATION OF PERSONNEL]{.underline}**

Personnel performing eddy current inspections shall be qualified and
certified in accordance with NAS 410. Personnel making accept/reject
decisions shall be certified to at least Level II in eddy current
testing. Personnel performing inspections on fracture critical
components shall, at a minimum, be certified to Level II in eddy current
testing.

**9.0 [DEFINITIONS]{.underline}**

90/95 The point where the 95% lower confidence bound on the Probability
of Detection (POD) vs. Crack size curve crosses 90% POD.

ASTM American Society for Testing and Materials

Compound Corner A corner formed by intersection of three or more
surfaces. Internal corner is concave in shape and external corner is
convex in shape.

EDM Electrical Discharge Machining

Final Inspection The final inspection performed for the acceptance of
the component.

Fracture Critical Classification which assumes that fracture or failure
of the

Component component resulting from the occurrence of a crack will result
in a catastrophic hazard. Fracture critical components will be
identified as such on the engineering drawing.

Indication Evidence of a discontinuity that requires interpretation to
determine its significance.

In-Process Inspections which occur during manufacturing before a
component is in final form.

In-Service Inspections performed on components that are in use or
storage.

NAS National Aerospace Standard

SAE SAE International

Special NDE A fracture control term denoting nondestructive inspection
personnel, procedures, and equipment with a demonstrated capability to
reliably (90/95) detect flaws smaller than those normally detected by
typical procedures.