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ULTRASONIC
EXAMINATION OF DOT CYLINDERS
By
UltraTest, a Division of FIBA Technologies, Inc.
Thank
you for your interest in learning more about UltraTest/FIBA’s
state-of-the-art cylinder requalification system.
UltraTest is a division of FIBA Technologies,
Inc in Millbury, MA.
Since 1958, FIBA has served the industrial
gas market and engaged in the manufacture, requalification,
leasing and selling of high-pressure and cryogenic
equipment in support of the compressed gas and
chemical industries.
As
part of our leasing and retest programs we have
tested thousands of tubes and over 2,000,000 cylinders.
During that time, we have continued to
look for better methods and technology to provide
the safest equipment in the marketplace. We introduced
Acoustic
Emission Testing (AET) of modular tube
trailers and currently have more teams in the
field than all other companies in the U.S., Canada
and Mexico combined.
Knowing
the advantages that an automated ultrasonic examination
(UE) system would give us, we began our research
and evaluation of various systems in the late
‘80’s. Even
after we focused on our current systems, for several
years we tested equipment, computers and several
thousand cylinders to generate the data we required
to be granted authorization to allow us to substitute
UE testing in place of hydrostatic testing to
requalify compressed gas cylinders.
Today, FIBA is the recognized pioneer and
leader in UE of DOT cylinders and tubes.
Based
upon our application, on October 27,1993 the U.S.
Department of Transportation (DOT) granted
us special permit
DOT-SP
10922, which authorized us to employ UE
as an alternative to hydrostatic testing of DOT-3A
and DOT-3AA compressed gas cylinders.
In June of 2001 we were granted special
permit
DOT-SP
12607 to test certain DOT-3AL aluminum
cylinders.
Obviously, UE provides tremendous advantages
over hydrostatic testing.
These advantages include:
UE
testing of cylinders is no longer a revolutionary
“new” concept in cylinder requalification.
Instead, UE has become the preferred test
method of all major industrial gas companies and
requalifiers because it provides cylinder requalification
of the highest integrity; thus providing enhanced
safety to both the user and shipper.
FAQs
About the UltraTest/FIBA UE Test Equipment
The
following is a list of questions that are frequently
asked about FIBA/UltraTest Division’s compressed
gas cylinder Ultrasonic Examination (UE) requalification
system.
Please note that the information and comments
in our answers are general in nature and are not
meant to replace information or requirements set
forth in our DOT Special Permits or in the U.S. Code
of Federal Regulations.
We welcome your comments and added questions.
Q.
Will UE reject more of my cylinders than the hydrotesting
system we are currently using?
A.
Not necessarily.
Our research and testing of over 2,000,000
cylinders to date has found that we have rejected
less than 1% of those tested. However, the cylinders
that we do reject are those that for safety’s
sake should be taken of UE of service.
Q.
Why would UE reject less cylinders than hydrotesting?
A.
In hydrotesting, leaking seals, operator interpretations,
poor burette readings and human error can all
reject cylinders that are still operational.
In the FIBA UltraTest UE system we remove
improper testing and human error from the equation.
Q.
Can you star and plus rate a cylinder?
A.
Yes, if the cylinder has previously been star
and plus rated and meets the DOT and CFR requirements
concerning lading and age, the star and plus can
be placed on the cylinder.
Q.
Can you requalify aluminum cylinders?
A.
Yes, FIBA received special permit (DOT SP-12607) in
July 2001, which
allows for the ultrasonic examination of
certain 3AL cylinders in addition to 3A and 3AA
cylinders authorized in 1993 under DOT SP-10922. FIBA’s new UE system has been designed to accommodate
the software necessary to meet the rejection criteria
currently required by the DOT for 3AL cylinders
made of 6061 aluminum alloy.
Q.
How many cylinders a day can you test by FIBA
Ultra Test UE?
A.
When the cylinders are properly prepared by the
cylinder owner, the UE operator can process over
25 cylinder per hour (i.e. 150-200 cylinders per
day).
Q.
Can any company be in the Ultrasonic Examination
business?
A.
Yes, any company can enter into the Ultrasonic
Examination business provided that the employees
of that company are trained and certified by FIBA
Ultra Test Division and registered with the DOT.
This is necessary because UltraTest holds the
special permit with the DOT and is therefore responsible
for reporting the results of all tests. Additionally,
some form of a cooperative agreement between FIBA
Ultra Test and the retest company must be in place,
which would make both companies responsible for
the test results.
Q.
How can a UE requalification do as well as a check
for elastic expansion?
A.
The primary if not the only, failure mode of cylinders
that fail hydrotest is expansion directly correlated
to thinning or excessive corrosion of cylinder
walls. That method calculates wall thickness by
indirect calculations based on permanent and elastic
expansion. UE does this measurement directly and
accurately.
Q.
How can UE detect a cylinder that has been exposed
to a fire?
A.
If the fire was hot enough the plastic deformation
and cracks so formed can be detected. If the cylinder
has only been partially burned, and then repainted,
the UE would probably miss it. However, if someone
were trying to hide such an occurrence, they would
be dealing in fraud. Someone dealing in fraud
could also avoid the hydrotesting. UE is not a
magic wand.
Q.
Would UE find an arc burn?
A.
UE will detect points that go below minimum wall
thickness from either an internal external flaw.
Most rejections due to arc burns are found during
the mandatory visual examination based on CGA
Standard C‑6. This test is not eliminated
during FIBA Ultra Test’s UE testing, and from
the position of the cylinder on the transport
conveyor FIBA Ultra Test personnel can examine
the cylinder better than during normal hydrotesting.
Q.
Does the valve ever need to be removed during
the test?
A.
No. The
latest rejection criteria invoked by the DOT addresses
the potential for internal corrosion or pitting
in certain wet gas cylinders.
Cylinders that are suspect of internal
corrosion and/or contaminants may be inspected
internally, if desired.
Q.
Do we need to empty or drain the cylinder during
testing of toxic gases?
A.
No. But
it is recommended that all cylinders containing
such gases be emptied as a precaution. However,
it is not necessary to empty the cylinder to perform
UE.
Q.
Isn't the internal visual inspection important
to find contaminants and oil in the cylinder?
A.
No. If
a cylinder is suspected of having been contaminated
you must either test the gas for the suspected
contaminant or pull the valve and examine the
cylinder. You should not wait for the
next requalification. Note that just because
you need not devalve and internally inspect a
cylinder for UE, nothing prevents you from doing
such a procedure if your policy requires it. We
highly recommend removal of any valves that are
suspect to internal cylinder contamination.
Q.
Why aren’t the necks and bottoms checked during
the UE requalification process?
A.
Because of the design of 3A, 3AA and 3AL cylinders,
the shoulder and bottom are low stress areas,
with thicker material. The cylinder is examined
from the transition area down through the knuckle
radius.
Q.
Will internal lading affect the tests (UE detection)?
Specifically will cylinders that
still have liquefied product in them give you
difficulties during testing?
A.
No. Product
would not have the same physical properties of
the steel being tested, therefore the instant
the sonic velocity changes, the system senses
it has reached the end of the steel.
Q.
Based on track record, how do I know which
UE system is the best choice for my company?
A. FIBA
is the acknowledged leader in the
use of ultrasonic technology to test cylinders.
Since 1993, FIBA has installed over 40 systems
across the country to test cylinders – no one
else even approaches that number. Every U.S. major
industrial gas company and many large retesters
utilize FIBA’s UE systems to test cylinders or
tubes. As stated before, FIBA’s UE systems have
tested well over 2 million cylinders to date,
far more than any other UE provider.
FIBA is the preferred choice - without
question!
Q.
How Does The FIBA/UE Ultrasonic Detection System
Work?
A.
An array of multiple, ultrasonic transducers are
mounted in a customized shoe.
The compressed gas cylinder is rotated
on a supporting set of wheels, which rotate the
cylinder and an encoder built into the mechanism,
which positions the head and the transducers.
As the system operates, the readings are
taken as a function of rotation, not time.
The readings are taken at specific intervals
(helix) in a pattern that overlaps by 110%.
FlBA’s
special permit is based upon measuring the wall thickness,
area corrosion and line corrosion, rejecting any
cylinder that has a wall section below the cylinder
minimum wall thickness prescribed in the specifications
for 3A, 3AA and 3AL cylinders.
Many of these values are consolidated and
listed in CGA C‑6.
The system also employs sensors that are
oriented at a 45o angle, which can
detect cracks or pitting that may have the potential
for infringing on the allowable wall thickness
of the cylinder.
In
the case of the Ultrasonic Examination system,
the thickness is measured by one set of detectors
that can detect variations of less than 0.002
inches from nominal. In addition, the remaining
detectors, focused on the same spot, are bilateral
and can detect aberrations (such as cracks and
flaws) in the longitudinal, transverse and oblique
directions.
Each
detector has its own separate amplifier and data
channel which records the results to the master
computer system as unique values, not an average.
(Some other UE systems, that depend on lateral
arrays, record test results as an average,
rather than as unique valves.) The computer is designed to sequence the
data channel electronics between transmit and
receive modes.
This ensures an appropriate time delay
between energizing the transducers and looking
for echoes from those transducers.
The design allows for over 2,000 pulses
per second, but for practical purposes has been
set to take a specified number of readings per
inch based on the rotation of the encoder.
This system allows re-qualification of cylinders without
having to remove the valve or remove the product.
The test process does not violate any EPA regulations,
which can be a concern when testing hydrostatically
and disposal of the effluent is a consideration
when flushing hydrotest water into local sewage
systems.
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