Getting NDT Right in MT and PT

imeche.org
ENGINEERING TRAINING
SOLUTIONS
GETTING NDT RIGHT IN
MT AND PT
Phil Raw
BSc (Hons) NDT

imeche.org
CAREER HISTORY
• 27 years experience in the NDT industry
• Holder of PCN, ASNT & EN 4179 Level 3
certification in multiple methods also BSc
Honours Degree in NDT
• Employed by Argyll-Ruane Ltd since 2001
as a Level 3 Consultant, Trainer and
Examiner

imeche.org
GETTING NDT RIGHT
MAGNETIC PARTICLE AND PENETRANT TESTING
As a trainer at Argyll-Ruane Ltd it is my job to teach NDT personnel
how to “get NDT right”
As a consultant I work for my clients as a Responsible Level 3 and
then my job entails making sure NDT personnel are getting NDT right.
Over the years I have witnessed many occasions when NDT has not
been done right and today I will discuss some of these incidents.
Some of the consequences of these incidents have lead to individuals
being dismissed, or been very expensive to correct.

imeche.org
Why is getting NDT right so important?
The British Institute of NDT states: Non-destructive testing and
inspection are vital functions in achieving the goals of efficiency
and quality at an acceptable cost.
In many cases, these functions are highly critical; painstaking
procedures are adopted to provide the necessary degree of quality
assurance.
The consequences of failure of engineering materials, components and
structures are well known and can be disastrous.
GETTING NDT RIGHT

imeche.org
It is an increasing requirement of quality assurance systems that a
company's technicians are able to demonstrate that they have the
required level of knowledge and skill.
This is particularly so since NDT and inspection activities are very
operator dependent and those in authority have to place great reliance
on the skill, experience, judgement and integrity of the personnel
involved.
Indeed, during fabrication, NDT and inspection provides the last line of
defence before the product enters service, whilst once a product or
structure enters service, in-service NDT is often the only line of defence
against failure.
GETTING NDT RIGHT

imeche.org
Basically the job you do is not an ordinary job – the job you do is
critical and in many cases lives can depend on you doing your job
correctly.
Not getting NDT right is not an acceptable option, if we get NDT
wrong it can have tragic consequences.
The next few slides show what can happen if NDT has gone wrong.
GETTING NDT RIGHT

imeche.org
On 19th July, 1989, a United Airlines
DC-10-10, experienced a
catastrophic in flight failure of the No.
2 engine.
This engine failure led to the
discharge of the stage 1 fan disk
assembly parts from the No. 2 engine
which led to the loss of all three
hydraulic systems powering the
flight controls.
GETTING NDT RIGHT

imeche.org
The crew experienced severe difficulties controlling the airplane, which
subsequently crashed during an attempted landing at Sioux Gateway
Airport.
There were 285 passengers and 11 crewmembers on-board, 1 flight
attendant and 110 passengers were fatally injured, 47 suffered serious
injuries, 125 suffered minor injuries and only 13 people on board were
uninjured.
GETTING NDT RIGHT

imeche.org
During its 17 year service life the engines in which the accident disk
was installed were overhauled, disassembled and inspected using
fluorescent penetrant inspection in 1972, 1973, 1976, 1978 1982
and finally in February 1988 17 months before the accident.
The NTSB concluded that the fatigue crack was likely to have been
between 12.0mm to 12.6mm surface length at the time of the last
fluorescent penetrant inspection, the minimum detectable defect length
in the critical disk bore area is 2.54mm when using fluorescent
penetrant inspection therefore the fatigue crack should have been
detected at the last inspection.
GETTING NDT RIGHT

imeche.org
The NTSB reviewed the technique used to inspect the disk and one
possibility for the failure of several inspections carried out after the
fatigue crack had exceeded the minimum detectable defect size was
the fact that the disk was suspended by a cable through the bore.
To fully apply the penetrant and later the developer and to fully
inspect the bore including the area obscured by the cable, the
operator has to physically rotate the part.
GETTING NDT RIGHT

imeche.org
It is possible that the inspectors may not have correctly processed or
viewed the bore area due to the cable, or that during rotation the cable
obliterated the indication or caused loose developer to fall on to the
crack and obscure the indication.
The NTSB also consider that there is a strong chance the inspectors
were experiencing inattentional blindness. This type of disk tends to
produce indications near dove tail posts and rarely in the bore, this
could cause inspectors to inspect the bore with less attention.
GETTING NDT RIGHT

imeche.org
The NTSB considers the probable cause of the accident was the
inadequate consideration given to human factors limitations in the
inspection and quality control procedures used by the engine overhaul
facility.
Inspectors tend to work independently and have little or no supervision
and hence there is no redundancy to prevent human error.
This resulted in several unsuccessful inspections which failed to locate
a detectable sized fatigue crack located in a critical area of the fan disk.
GETTING NDT RIGHT

imeche.org
GETTING NDT RIGHT

imeche.org
In July 1996, a Delta Airlines flight suffered an uncontained engine
failure during routine take off from Pensacola airport.
The left hand side number 1 engine; a Pratt & Whitney JT8D-219 on
the McDonnell Douglas MD88 was destroyed during the incident.
The front compressor front hub (fan hub) suffered a catastrophic
fatigue failure.
Uncontained engine debris penetrated the rear fuselage on the left
hand side and tragically two people were killed, one person on the
other side of the aisle suffered serious injuries and one passenger
sustained serious injuries during the cabin evacuation.
GETTING NDT RIGHT

imeche.org
The NTSB investigation revealed that the failed titanium fan hub had
fractured radially in two places; one of the radial fractures contained
a fatigue crack that originated at two locations on the inboard side in
a tie rod hole, at 7.79mm and 14.04mm from the aft edge of the tie rod
hole respectively.
The fatigue fracture extended 38mm radially inboard towards the
centre of the engine, the rest of the fracture surface was considered to
be the catastrophic final overstress failure.
GETTING NDT RIGHT

imeche.org
The last inspection that the accident hub received was a fluorescent
penetrant inspection carried out in October 1995 by a Delta airlines
level 1 certified penetrant inspector with 11 months experience.
The FAA inspected the Delta airlines testing facility and determined
that there was no assurance that parts received by penetrant
inspectors were “clean enough for an adequate penetrant test”.
The hubs were not pre cleaned prior to penetrant testing by qualified
NDT inspectors; they were cleaned by shop floor cleaning operatives
with no NDT training and who were not made aware of the “criticality
of the engine components and the end purpose for which the
components were being cleaned”.
GETTING NDT RIGHT

imeche.org
The final cleaning operations involved immersing parts in a hot
water rinse and then flash drying.
For flash drying to work effectively and leave no water trapped in
any discontinuities that would prevent penetrant entering the
discontinuity, the part must reach the temperature of the water
which must be between 65°C to 93°C.
Cleaning operatives did not measure part temperature and used
only their sense of touch to feel if the part was hot enough; the
water temperature was only checked on a weekly basis.
GETTING NDT RIGHT

imeche.org
The report also looked at human factors as a potential cause of the
crack being missed; these hubs are very large and are a very
complicated shape and can take 40 minutes to two hours to inspect
fully.
Any distraction during this period could cause the inspector to fail to
resume the inspection where he left off, and with penetrant inspection
unless you physically mark an area you do not know if it has been
inspected or not.
GETTING NDT RIGHT

imeche.org
Delta inspectors did not mark inspected areas or use a grid pattern to
assist inspection.
The NTSB also considered that there was a low expectation amongst
inspectors of finding a crack; the supervisor stated that he was not
aware that any cracks had ever been found on this type of hub at
Delta.
The conclusion was that in-attentional blindness could have caused
the inspector to overlook or minimise the significance of an indication.
GETTING NDT RIGHT

imeche.org
The NTSB concluded that the probable cause of the accident was
• the failure of the fluorescent penetrant inspection process
to detect a detectable fatigue crack initiating from an area of
altered microstructure that was created during the drilling
process and
• lack of sufficient redundancy in the in-service inspection
program.
GETTING NDT RIGHT

imeche.org
Next lets have a look at some examples of how I
have seen NDT not done correctly.
GETTING NDT RIGHT

imeche.org
Ensure you are correctly certified for the work you are
being asked to do.
Case Study: An aerospace manufacturer supplying to an engine
manufacturer uses an EN 4179 certification scheme – (employer
based certification) used NDT contractors who held EN 4179
certification issued by their employer. The written practice of the
aerospace manufacturer has not been complied with and the
contractors were not correctly certified to test parts.
GETTING NDT RIGHT

imeche.org
• The parts they had penetrant tested underwent further
manufacturing operations which meant the parts could not be
re-tested by correctly certified NDT personnel.
• The engine manufacturer would not accept the £200k of parts
tested by the contractors and one individual left the company
over the issue.
GETTING NDT RIGHT

imeche.org
Ensure your eye sight is tested annually.
Case Study: During a routine audit of an NDT facility the
vision test certificate of one individual had expired some
weeks previously and the operator had tested many parts
that were supplied to an aerospace facility.
As his vision test was overdue his certification should have
been suspended and he should not have tested any parts
until he had passed an eye test.
GETTING NDT RIGHT

imeche.org
When the customer was informed, they sent back all the
parts tested by the inspector from the date his vision
certificate had expired and demanded it was re-tested at the
suppliers’ expense.
GETTING NDT RIGHT

imeche.org
Ensure you understand and comply with NDT techniques
and procedures.
Case Study: A client conducted an audit of a suppliers NDT facility
and watched an operator inspecting some of their parts. The
operator did not follow the approved NDT technique and therefore
did not correctly test the part.
The auditor twice asked the operator at the conclusion of the
inspection if he was happy that he had fully completed the inspection
and the operator said yes.
GETTING NDT RIGHT

imeche.org
The client demanded the operator’s certification was immediately
suspended and that all material he had tested for them had to be
re-inspected. The inspector left the company over the issue.
GETTING NDT RIGHT

imeche.org
Case Study: Many penetrant testing process specifications
specify using a solvent wipe technique to evaluate indications.
The process specifications usually specify wiping once and only
once across the indication with a solvent damped cotton swab and
then applying developer.
On many occasions during NADCAP compliance audits NDT
inspectors have been seen to wipe across indications more than
once thus incurring a non-conformance.
GETTING NDT RIGHT

imeche.org
Ensure you carry out shift checks correctly.
Case Study: During an audit of the NDT facility of a company that
produces motorsport racing engines, the shift check log was
reviewed and the result recorded for UV-A inspection lamp
irradiance was exactly the same figure for every day for six months.
The operator was then asked to demonstrate the test and the result
was approximately half the value of the recorded figure for the test
“carried out” only an hour earlier.
GETTING NDT RIGHT

imeche.org
Further investigation revealed other clear instances where the
operator was not carrying out the shift checks just writing down
numbers in the log sheet.
The operator was dismissed by his employer for unethical
behaviour.
GETTING NDT RIGHT

imeche.org
Ensure you understand how to use NDT equipment.
Case Study: A manufacturing company had numerous customer
complaints of defective material being delivered.
The company blamed the NDT inspectors and called me in to carry
out refresher training.
GETTING NDT RIGHT

imeche.org
The inspection area on the shop floor was dimly lit from high
overhead lighting, when this was checked with a photometer a
reading of only 110 lux was observed, the process specification
required a minimum of 1000 lux.
The technician was misreading the photometer by a factor of 10
and claimed how he was reading it was how he had been
instructed to do so by the previous quality manager. The
technician was then instructed how to use this equipment
correctly.
GETTING NDT RIGHT

imeche.org
Once new lighting was installed the frequency of customer
complaints was reduced significantly.
GETTING NDT RIGHT

imeche.org
Ensure you never forget NDT method basics.
Case Study 1: A magnetic particle testing technique using bench
equipment was raised by a Level 2 and submitted for Level 3
approval.
The technique stated testing the part using magnetic flow followed
by a coil shot, this of course is basically testing the part twice using
longitudinal magnetisation and the part would not be tested for
defects in all possible orientations.
Had this technique been used defective parts could have ended up
on an aircraft.
GETTING NDT RIGHT

imeche.org
Case Study 2: A Level 2 NDT inspector raised a technique for
magnetic particle testing and submitted it for approval.
Upon review it was noted that the part was made of titanium! The data
card was rejected.
GETTING NDT RIGHT

imeche.org
Case Study 3: During an audit a magnetic particle testing data card
for bench equipment was reviewed, it was noted that the parts tested
with this data card were made of austenitic stainless steel.
The data card had been used to “test” these parts for over two years!
Operators were using correct test pieces to carry out shift checks but
were not using flux indicators on the parts under test.
GETTING NDT RIGHT

imeche.org
Case study 4: An audit was carried out on a facility manufacturing
car engine parts that was using an automatic magnetic particle
testing machine.
It was noted that the current flow shot stopped before the automatic
flow of ink stopped and was basically washing any indications away
as demonstrated when a flux indicator was applied.
No defects had ever been found whilst this equipment had been in
operation.
The timing of ink application was amended and the inspectors
started finding defects for the first time.
GETTING NDT RIGHT

imeche.org
Case study 5: During a performance review of an NDT inspector
using fluorescent penetrant it was noted that he was wearing
photochromatic spectacles in the UV-A inspection area.
He had been using these spectacles for several months.
GETTING NDT RIGHT

imeche.org
Keep an eye out for unethical behaviour
Case Study: During an audit of an NDT facility completed follower
cards were reviewed. The NDT penetrant testing operation had been
stamped off with the stamp of an NDT inspector that had died several
months previously.
The investigation found that a non NDT certified member of staff had
obtained the stamp and was using it to speed up production.
Considerable quantities of parts had been despatched to customers
without any NDT inspection!
GETTING NDT RIGHT

imeche.org
During NDT audits don’t panic just do your job normally
Case Study: As an observer during a NADCAP magnetic particle
testing compliance audit, it was observed that a young inspector was
very nervous.
He was testing some small parts in the heads of a bench unit and made
the mistake of handling the parts before he had inspected them under
the UV-A inspection lamp.
The auditor wrote this up as a non-conformance and the inspector had
to have a training session as part of the corrective actions.
GETTING NDT RIGHT

imeche.org
Ensure non NDT individuals do not abuse or use NDT
equipment.
Case Study: During a summer shutdown of a factory, the factory
floor received a shiny new coat of paint, certain shop floor
individuals who afterwards refused to identify themselves used the
fluorescent ink bath of the magnetic particle testing machine to clean
their brushes.
200 litres of fluorescent ink had to be replaced and a full shift had to
be spent cleaning the machine.
GETTING NDT RIGHT

imeche.org
Case Study: A large forging was tested with penetrant and a large
crack was found.
A shop floor handyman was assigned to re-work the forging by
grinding with an NDT inspector retesting the ground area to ensure it
was cleared.
After several sessions of grinding and retesting without clearing the
defect the NDT inspector went for a lunch break. When he returned
from lunch the forging was on the back of a lorry.
The handyman had “tested” the ground area and decided the defect
was clear.
He had in fact buried the defect under a thick layer of developer and
further grinding was required.
GETTING NDT RIGHT

imeche.org
Keep an eye open for the unexpected.
Case Study: During an audit of a fluorescent penetrant testing
facility, a Level 2 inspector was demonstrating how to carry out a test
for fluorescent penetrant contamination by taking a sample of
penetrant in a glass beaker and viewing this sample.
When I looked into the penetrant tank I saw something on the tank
bottom, the inspector put his hand in and retrieved a broken tube
from a fluorescent strip light.
GETTING NDT RIGHT

imeche.org
As these lights have coatings on the inside of the tube the penetrant
had to be discarded, the tank cleaned and replenished with fresh
penetrant.
GETTING NDT RIGHT

imeche.org
Ensure you review equipment calibration certificates.
Case Study: It is fairly common that photometers and radiometers
have to be adjusted by calibration engineers to bring them within
tolerance of the relevant standards.
Review calibration certificates and see if they have an “as received
condition” which exceeds mandated tolerance requirements i.e. ±
5% and then an “after adjustment figure” which does comply with
required tolerances. If this is the case a risk assessment is to be
carried out.
GETTING NDT RIGHT

imeche.org
For example in the as received condition a radiometer has an
accuracy of + 10%, this means that it is reading the UV-A output
from inspection lamps 10% higher than the actual lamp output;
1000µW/cm² as read is actually only 900µW/cm².
A risk assessment would require reviewing the shift check results for
UV-A lamp output since the previous radiometer calibration and find
the lowest lamp output reading, subtract 10% from this figure and if
this is still above the minimum required by the relevant standard
there is no impact on product.
GETTING NDT RIGHT

imeche.org
Ensure you use equipment correctly.
Case Study 1: Electromagnetic yokes should be checked with a test
weight to determine if the lifting power of the yoke is sufficient.
During audits it is common to see NDT inspectors using flux indicator
strips with electromagnetic yokes and neglecting to use the test
weight.
GETTING NDT RIGHT

imeche.org
The problem is that if you put a flux indicator on any surface even
non ferromagnetic materials such as a piece of wood or a slice of
bread, spray ink and energise the electromagnet the magnetic flux
between the poles will form an indication on the flux indicator –
clearly we can’t test a plank of wood!
A flux indicator with an electromagnet can only show flux direction,
which we should know anyway but will not determine if the flux
density is adequate.
GETTING NDT RIGHT

imeche.org
Case Study 2: During a performance review an operator was asked
to test a part in a magnetic particle testing bench.
He set up a current flow shot and placed a flux indicator on the part
but in the wrong direction, when no indication formed he stated the
machine was not working.
He was then embarrassed when instructed to turn the strip at 90
degrees to the first orientation and three strong indications suddenly
appeared.
GETTING NDT RIGHT

imeche.org
Avoid distractions during testing
Case Study: An operator was distracted by an urgent telephone call
halfway through magnetic particle inspection of a large forging.
When he returned to the job he thought he had completed the
inspection and released it to the next operation.
Another member of staff spotted a crack in the untested half of the
forging some time later.
Marking tested areas on large parts can help stop this type of
mistake.
GETTING NDT RIGHT

imeche.org
Don’t just look for small discontinuities
Case Study: An aero engine shaft was returned from a customer
that had been in-service in an engine for some time.
During a routine engine strip down the shaft was tested using
magnetic particle techniques and a crack approximately 100mm long
was found.
Metallurgical analysis determined that this was not an in-service
defect it was a manufacturing defect and fortunately had not
propagated during service.
GETTING NDT RIGHT

imeche.org
The company that made the shaft concluded that NDT inspectors
seldom found defects on these components and when they did they
were only 2 – 3mm long maximum.
The crack was running circumferentially and may have been
mistaken for a machining line as the inspectors never expected a
crack that big to be found.
GETTING NDT RIGHT

imeche.org
Ensure you are correctly trained to operate NDT equipment
Case Study: A performance review was carried out on a NDT
inspector who was using a magnetic particle testing bench unit.
The inspector put a part in the bench sprayed ink on it and started
inspecting it with a UV-A inspection lamp. He had not pressed the
button to energise the current!
When asked why he said he had never been told to press the button
and did not know what it was for.
Worryingly he had been “testing” work like this for over a year!
GETTING NDT RIGHT

imeche.org
Be aware of human factors in NDT
The reliability of NDT can be significantly influenced by the
environment in which parts are processed and inspected.
Consideration of human factors is an important element in achieving
process capability.
Human factors are typically dependent on a large number of
influences such as fatigue, environment, stress and complexity of task.
GETTING NDT RIGHT

imeche.org
How can these human factors be addressed?
• Fatigue – rotation of tasks, duration of inspection times
• Environment – working space, inspection booth extraction,
comfort level
• Stress – improved working practices, minimise inspection
interruption
• Complexity of task – appropriate equipment, fixtures and
training
GETTING NDT RIGHT

imeche.org
Conclusions
MT and PT are in general easy methods to get right but as we have seen
in this presentation there are many pitfalls we need to avoid, unfortunately
it can be all too easy to get NDT wrong.
• We must never be complacent,
• We must never cut corners,
• We must guard against making mistakes.
We must never forget how important NDT is; ultimately
peoples lives depend on us to get NDT right.
GETTING NDT RIGHT

THANK YOU
For more information please contact:
Phil Raw
p_raw@imeche.org
imeche.org/arl

Getting NDT Right in MT and PT

Recommended

Recommended

More Related Content

What's hot

What's hot (20)

Viewers also liked

Viewers also liked (14)

Similar to Getting NDT Right in MT and PT

Similar to Getting NDT Right in MT and PT (20)

More from Institution of Mechanical Engineers (IMechE)

More from Institution of Mechanical Engineers (IMechE) (12)

Recently uploaded

Recently uploaded (20)

Getting NDT Right in MT and PT