ISO 10461:2005

INTERNATIONAL ISO
STANDARD 10461
Second edition
2005-02-15
Gas cylinders — Seamless
aluminium-alloy gas cylinders —
Periodic inspection and testing
Bouteilles à gaz — Bouteilles à gaz sans soudure en alliage
d'aluminium — Contrôles et essais périodiques

Reference number
©
ISO 2005
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©  ISO 2005
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ii © ISO 2005 – All rights reserved

Contents Page
Foreword. iv
Introduction . v
1 Scope. 1
2 Normative references . 1
3 Intervals between periodic inspections and tests. 1
4 List of procedures for periodic inspections and tests. 2
5 Identification of cylinder and preparation for inspections and tests . 2
6 Depressurization and de-valving procedures. 2
7 External visual inspection. 3
8 Check of internal condition. 4
9 Supplementary tests. 4
10 Inspection of cylinder neck. 5
11 Pressure test or ultrasonic examination . 5
12 Inspection of valve and other accessories.15
13 Cylinder repairs. 15
14 Final operations . 15
15 Rejection and rendering cylinders unserviceable. 18
Annex A (informative) Intervals between periodic inspections and tests . 19
Annex B (normative) Description and evaluation of defects and conditions for rejection of
seamless aluminium-alloy gas cylinders at time of visual inspection. 20
Annex C (normative) Procedure to be adopted when de-valving and/or when it is suspected that a
cylinder valve is obstructed. 25
Annex D (informative) Cleaning of aluminium-alloy gas cylinders . 28
Annex E (informative) Volumetric expansion testing of gas cylinder. 29
Annex F (informative) Inspection and maintenance of valves and their junctions: recommended
procedures. 37
Annex G (informative) Test date rings for gas cylinders. 38
Bibliography . 39

Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies
(ISO member bodies). The work of preparing International Standards is normally carried out through ISO
technical committees. Each member body interested in a subject for which a technical committee has been
established has the right to be represented on that committee. International organizations, governmental and
non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the
International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of technical committees is to prepare International Standards. Draft International Standards
adopted by the technical committees are circulated to the member bodies for voting. Publication as an
International Standard requires approval by at least 75 % of the member bodies casting a vote.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. ISO shall not be held responsible for identifying any or all such patent rights.
ISO 10461 was prepared by Technical Committee ISO/TC 58, Gas cylinders, Subcommittee SC 4,
Operational requirements for gas cylinders.
This second edition cancels and replaces the first edition (ISO 10461:1993), which has been technically
revised.
iv © ISO 2005 – All rights reserved

Introduction
The principal aim of a periodic inspection and testing procedure is to be satisfied that at the completion of the
inspection and test, the cylinders (single or those from bundles) can be reintroduced into service for a further
period of time.
The inspection and test are to be carried out only by persons who are authorized under the relevant
regulations and competent in the subject to assure all concerned that the cylinders are fit for continued safe
use.
The results of inspection and testing for the cylinders that are specified in this International Standard
determine whether a cylinder should be returned to service.

INTERNATIONAL STANDARD ISO 10461:2005(E)

Gas cylinders — Seamless aluminium-alloy gas cylinders —
Periodic inspection and testing
1 Scope
This International Standard deals with seamless aluminium-alloy transportable gas cylinders intended for
compressed and liquefied gases under pressure, of water capacity from 0,5 l to 150 l; it also applies, as far as
practical, to cylinders of less than 0,5 l water capacity.
This International Standard specifies the requirements for periodic inspection and testing to verify the integrity
of such gas cylinders for further service.
This International Standard does not apply to periodic inspection and testing of acetylene cylinders or
composite cylinders with aluminium-alloy liners.
2 Normative references
The following referenced documents are indispensable for the application of this document. For dated
references, only the edition cited applies. For undated references, the latest edition of the referenced
document (including any amendments) applies.
ISO 9712, Non-destructive testing — Qualification and certification of personnel
ISO 11114-2:2000, Transportable gas cylinders — Compatibility of cylinder and valve materials with gas
contents — Part 2: Non-metallic materials
ISO 11621, Gas cylinders — Procedures for change of gas service
ISO 13341, Transportable gas cylinders — Fitting of valves to gas cylinders
ISO 13769, Gas cylinders — Stamp marking
3 Intervals between periodic inspections and tests
A cylinder shall be due for a periodic inspection and test on its first receipt by a filler after the expiry of the
interval in accordance with the requirements of the United Nations Recommendations on the Transport of
Dangerous Goods, Model Regulations or as specified by national or international authorities (see examples in
Annex A).
Provided the cylinder has been subjected to normal conditions of use and has not been subjected to abusive
and abnormal conditions rendering the cylinder unsafe, there is no general requirement for the user to return a
gas cylinder before the contents have been used even though the periodic inspection and test interval may
have lapsed.
It is the responsibility of the owner or user to submit the cylinder for a periodic inspection and test within the
interval specified by national or international authorities, or as specified in the relevant cylinder design
standard if this is shorter.
4 List of procedures for periodic inspections and tests
Each cylinder shall be submitted to periodic inspections and tests. The following procedures, where applicable,
form the requirements for such inspections and tests and are explained more fully in later clauses:
a) identification of cylinder and preparation for inspections and tests (Clause 5);
b) depressurization and de-valving procedures (Clause 6);
c) external visual inspection (Clause 7);
d) check of internal condition (Clause 8);
e) supplementary tests (Clause 9);
f) inspection of cylinder neck (Clause 10);
g) pressure test or ultrasonic examination (Clause 11);
h) inspection of valve and other accessories (Clause 12);
i) cylinder repairs (Clause 13);
j) final operations (Clause 14);
k) rejection and rendering cylinders unserviceable (Clause 15).
It is recommended that these procedures be performed in the sequence listed. In particular, the check of
internal condition (Clause 8) should be carried out before the pressure test or, although not required, before
the ultrasonic examination (Clause 11).
Cylinders that fail an inspection or test shall be rejected (see Clause 15). Where a cylinder passes the above
procedures, but when the condition of the cylinder remains in doubt, additional tests shall be performed to
confirm its suitability for continued service (see Clause 9) or the cylinder shall be rendered unserviceable.
Depending on the reason for the rejection, some cylinders may be recovered (see Annex B).
The inspections and tests shall be carried out only by persons who are competent in the subject and
authorized under the relevant regulations.
Mechanical properties of aluminium-alloy cylinders can be affected by heat exposure. Therefore, the
maximum temperature for any operation shall be limited according to the manufacturer's recommendations
(see 14.2.2).
5 Identification of cylinder and preparation for inspections and tests
Before any work is carried out, the relevant cylinder data (e.g. see ISO 13769) and its contents and ownership
shall be identified (e.g. from the labelling and stamping). Cylinders with incorrect or illegible markings or
unknown gas contents shall be set aside for special handling.
6 Depressurization and de-valving procedures
6.1 General
Cylinders to be internally inspected or tested by a pressure test are required to be depressurized and de-
valved. Cylinders not internally visually inspected and tested by ultrasonic examination do not require
complete depressurization and de-valving unless the ultrasonic examination indicates there is an
unacceptable flaw present and the inspector wishes to further investigate (see 11.4.6).
2 © ISO 2005 – All rights reserved

6.2 Cylinders requiring depressurization
Cylinders shall be depressurized in a safe, controlled manner before proceeding. Particular attention shall be
given to cylinders containing flammable, oxidizing, corrosive or toxic gases to eliminate risks at the internal
inspection stage.
Before removing any pressure-retaining accessory (valve, flange, etc.), a positive check shall be performed to
ensure that the cylinder does not contain any gas under pressure. This can be performed as described in
Annex C using a device such as shown in Figure C.1.
Cylinders with inoperative or blocked valves shall be treated as outlined in Annex C.
Similarly in the case of cylinders disassembled from bundles not equipped with cylinder valves, the connecting
tee junctions shall also be checked to determine whether the gas is able to pass freely from the cylinders
using for example the device shown in Figure C.1.
Provided the requirements previously stated have been complied with, the cylinder shall be depressurized
safely and the valve shall be removed.
6.3 Cylinders not requiring de-valving
Cylinders shall be depressurized below 5 bar to perform ultrasonic examination.
For cylinders being inspected by the ultrasonic method, refer to Clause 8.
7 External visual inspection
7.1 Preparation for external visual inspection
If a cylinder's external condition prevents or hinders a proper visual inspection of the surface, then the cylinder
shall be prepared before the inspection. The cylinder shall be cleaned and have all loose coatings, corrosion
products, tar, oil or other foreign matter removed from its external surface by a suitable method, e.g. brushing,
water jet abrasive cleaning, chemical cleaning or other suitable methods (see Annex D or consult the cylinder
manufacturer). Alkaline solutions and paint strippers that are harmful to aluminium and its alloys shall not be
used. The method used to clean the cylinder shall be a validated, controlled process. Care shall be taken at all
times to avoid damaging the cylinder or removing excess amounts of cylinder wall (see Annex B).
If fused nylon, polyethylene or a similar coating has been applied and the coating is seen to be damaged or it
prevents a proper inspection, then the coating shall be stripped. If the coating has been removed by the
application of heat at a temperature exceeding the limits specified in 14.2.2 or shows signs of heat damage,
the manufacturer shall be consulted before the cylinder is returned into service and the necessary tests and
inspections carried out.
7.2 Inspection procedure
The external surface of each cylinder shall then be inspected for
a) dents, cuts, gouges, bulges, cracks, laminations or excessive base wear;
b) heat damage, torch or electric-arc burns (as specified in Table B.1);
c) corrosion (as specified in Table B.2);
d) other defects such as illegible, incorrect or unauthorized stamp markings, or unauthorized additions or
modifications; and
e) integrity of all permanent attachments (see B.2).
When inspecting for corrosion [see c)], special attention shall be given to areas where water could be trapped.
These include the entire base area, the junction between the body and the foot ring and the junction between
the body and the shroud.
For rejection criteria, see Annex B. Cylinders no longer suitable for future service shall be rendered
unserviceable (see Clause 15).
8 Check of internal condition
Cylinders shall be inspected internally to complete periodic inspection and testing requirements.
When the valve is removed, an internal visual inspection shall be performed.
For cylinders being examined by the ultrasonic method in lieu of the pressure test and when reference notches
as specified in 11.4.4.2.2 are used for calibration, the valve need not be removed. However, for aluminium-alloy
cylinders susceptible to sustained-load cracking, such as those manufactured from IAA 6351A or IAA 6082A
alloy, the shoulder and neck area shall be internally visually inspected; alternative non-destructive examination
methods, such as eddy current or ultrasonic examination, may be used if approved by the competent authority.
For cylinders that are internally visually inspected, adequate illumination shall be used to identify any defects
similar to those listed in 7.2 a) and 7.2 c). Precautions shall be taken to ensure that the method of illumination
presents minimum safety risk to the inspector while performing this operation. Any internal liner or coating that
may obstruct optimum internal visual inspection shall be removed. Any cylinder showing presence of foreign
matter or signs of more than light surface corrosion shall be cleaned internally by water jet abrasive cleaning,
flailing, steam jet, hot water jet, chemical cleaning, blasting with glass beads or other suitable method (see
Annex D or consult the cylinder manufacturer). Blasting with material other than aluminium or glass beads
shall be avoided; hard media could embed itself in the aluminium and result in contamination of the contents.
Alkaline solutions and paint strippers that are harmful to aluminium and its alloys shall not be used. The
method used to clean the cylinder shall be a validated, controlled process. Care shall be taken at all times to
avoid damaging the cylinder or removing excess amounts of cylinder wall in accordance with Annex B. If
cleaning is required, the cylinder shall be re-inspected after the cleaning operation.
For cylinders of non-corrosive gases and < 0,5 l water capacity with an internal neck diameter < 9 mm, the
following alternative methods may be substituted for the internal visual inspection.
 Looking for free moisture at the time of degassing the cylinder whilst in an inverted position and prior to
valve removal. If any moisture is present, the cylinder shall be rendered unserviceable.
 Looking for contamination, e.g. in the water used after the hydraulic test. If contamination is observed in
the hydraulic test fluid, the cylinder shall be rendered unserviceable.
9 Supplementary tests
Where there is doubt concerning the type and/or severity of a defect found on visual inspection, additional
tests or methods of examination shall be applied, e.g. ultrasonic techniques, check weighing or other
non-destructive tests.
When a hardness test is performed (e.g. see ISO 6506) or an alternative method is used (e.g. conductivity), it
shall meet at least the minimum required design hardness value. An alternative method may only be used if it
was employed at the time of cylinder manufacture, approved for use by the authorized body, and results and
approval recorded accordingly. When this value is not known, the cylinder shall be hardness tested both
before and after the stoving operation, and there shall be no appreciable decrease in the hardness value. All
hardness tests shall be performed on the parallel section of the cylinder, taking adequate care to ensure deep
impressions are not formed and deflection of the sidewall does not occur.
4 © ISO 2005 – All rights reserved

10 Inspection of cylinder neck
10.1 Cylinder to valve threads
When the valve is removed, the cylinder to valve threads shall be examined to identify the type of thread (e.g.
see ISO 11191 for 25E) and to ensure that they are
 clean and of full form,
 free of damage,
 free of burrs,
 free of cracks – examine thoroughly for evidence of cracks (see Annex B),
 free of other imperfections, e.g. corrosion.
Cracks manifest themselves as lines that run vertically down the thread and across the thread faces (see
Figure B.6). They should not be confused with tap marks (thread machining stop marks) (see Figure B.7).
Special attention shall be paid to the area at the bottom of the threads for the detection of shoulder cracks or
other defects (see Figure B.8).
10.2 Other neck surfaces
Other surfaces of the neck shall also be examined to ensure they are free of cracks or other defects (see
Annex B).
10.3 Damaged internal neck threads
Where necessary and where the manufacturer or the competent design authority confirms that the design of
the neck permits, threads may be re-tapped only by competent persons to provide the appropriate number of
effective threads. After re-tapping, the threads shall be checked with the appropriate thread gauge, e.g.
ISO 11191 for 25E threads.
10.4 Neck ring and collar attachment
When a neck ring/collar is attached, an examination shall be carried out to ensure that it is secure and to
inspect for external thread damage. A neck ring shall only be changed using an approved procedure. If it is
found that any significant damage to cylinder material has occurred by replacement of the neck ring/collar, the
cylinder shall be rendered unserviceable. If the neck ring has been reattached by welding or brazing, the
cylinder shall be rendered unserviceable.
11 Pressure test or ultrasonic examination
11.1 General
Each cylinder shall be submitted to either a pressure test or an ultrasonic examination.
WARNING — Appropriate measures shall be taken to ensure safe operation and to contain any
energy released. It should be noted that pneumatic pressure tests require more precautions than
hydraulic pressure tests since, regardless of the size of the container, any error in carrying out this
test is highly likely to lead to a rupture under gas pressure. Therefore, these tests shall be carried out
only after ensuring that the safety measures satisfy the safety requirements.
Each cylinder subjected to a hydraulic pressure test shall use a suitable liquid, normally water, as the test
medium. The hydraulic pressure test may be a proof pressure test or a volumetric expansion test as appropriate
to the design specification of the cylinder. The hydraulic proof pressure test may be replaced by a pneumatic
proof pressure test. Having decided to use one particular type of test, its result shall be final. The test pressure
shall be in accordance with the stamp markings of the cylinder.
Once a cylinder has failed one of the above-mentioned tests, none of the other test methods shall be applied to
approve the cylinder.
11.2 Proof pressure test
11.2.1 Preamble
The following proposes a typical method for carrying out the test. Any cylinder failing to comply with the
requirements of a proof pressure test shall be rendered unserviceable.
This test requires that the pressure in the cylinder be increased gradually until the test pressure is reached. The
cylinder test pressure shall be held for at least 30 s with the cylinder isolated from the pressure source, during
which time there shall be no decrease in the recorded pressure or evidence of any leakage. Adequate safety
precautions shall be taken during the test.
11.2.2 Test equipment
11.2.2.1 All rigid pipe work, flexible tubing, valves, fittings and components forming the pressure system of
the test equipment shall be designed to withstand a pressure of at least 1,5 times the maximum test pressure
of any cylinder that could be tested.
11.2.2.2 Pressure gauges shall be to Industrial Class 1 (± 1 % deviation from the end value) with a scale
appropriate to the test pressure (e.g. EN 837-1 or EN 837-3). They shall be checked for accuracy against a
calibrated master gauge at regular intervals and in any case not less than once a month. The master gauge
shall be calibrated in accordance with national requirements. The pressure gauge shall be chosen so that the
test pressure is between approximately one-third and two-thirds of the value capable of being measured on
the pressure gauge.
11.2.2.3 The design and installation of the equipment, the connection of the cylinders and the operating
procedures shall be such as to avoid trapping air in the system when a liquid medium is used.
11.2.2.4 All joints within the system shall be leak tight.
11.2.2.5 A suitable system control device shall be fitted to the test equipment to ensure that no cylinder is
subjected to a pressure in excess of its test pressure by more than the tolerances specified in 11.2.3.3.
11.2.3 Test criteria
11.2.3.1 More than one cylinder may be tested at a time provided that they all have the same test pressure.
If individual test points are not used, then in case of leakage all cylinders being tested shall be individually
retested.
11.2.3.2 Before applying pressure, the external surface of the cylinder shall be dry.
11.2.3.3 The pressure applied shall not be below the test pressure and shall not exceed the test pressure
by 3 % or 10 bar, whichever is lower.
11.2.3.4 On attaining the test pressure, the cylinder shall be isolated from the pump and the pressure held
for a minimum period of 30 s.
11.2.3.5 If there is a leakage in the pressure system, it shall be corrected and the cylinders retested.
6 © ISO 2005 – All rights reserved

11.2.4 Acceptance criteria
During the 30 s hold period the pressure as registered on the pressure gauge shall remain constant.
There shall be absence of visible leakage on the entire surface of the cylinder. This check can be made during
the 30 s hold. There shall be no visible permanent deformation.
11.3 Hydraulic volumetric expansion test
Annex E proposes typical methods for carrying out the test and gives details for determining the volumetric
expansion of seamless aluminium-alloy gas cylinders by the preferred water jacket method or the non-water
jacket method. The test methods, equipment and procedure chosen shall be approved by the authorized body.
The water jacket volumetric expansion test shall be carried out on equipment with a levelling burette, with a
fixed burette or with a weigh bowl. Care should be taken that the entire external surface of the cylinder is wet
without any bubbles.
The permanent volumetric expansion of the cylinder expressed as a percentage of the total expansion at test
pressure shall not exceed the percentage given in the design specification after the cylinder has been held at
test pressure for a minimum period of 30 s. If this figure for permanent expansion is exceeded, the cylinder shall
be rendered unserviceable.
11.4 Ultrasonic examination
11.4.1 Background
The ultrasonic examination on gas cylinders as described below is based on the ultrasonic examination of
pipes according to ISO 9305, ISO 9764 and ISO 10543. The special geometrical features of gas cylinders and
the boundary conditions for periodic inspections have been taken into account.
11.4.2 Scope
The ultrasonic examination (UE) of seamless aluminium-alloy gas cylinders (water capacity W 2 I) within the
framework of periodic inspections may be carried out in lieu of the tests specified in 11.2 and 11.3.
11.4.3 Requirements
11.4.3.1 General
The cylindrical part of the cylinder, the transition to the shoulder, the transition at the base and critical zones of
the base shall be examined ultrasonically with the help of an automated examination device (e.g. Figure 1).
For aluminium-alloy cylinders susceptible to sustained-load cracking, such as those manufactured from
IAA 6351 or IAA 6082 alloy, the transition area from the shoulder to the neck shall be examined. When such
an examination device is not able to do this outside the cylindrical part, a supplementary manual examination
shall be performed.
Cylinders that are suspected of fire or heat damage shall not be examined ultrasonically.
Key
1 ultrasonic examination transducers moving
2 ultrasonic examination equipment
3 cylinder moving
Figure 1 — Examples of two types of ultrasonic examination devices for gas cylinders
11.4.3.2 Examination equipment
The installation shall be able to scan the whole surface of the cylindrical part of the cylinder, including the
adjacent transitions to the base and shoulder. An examination system shall have a number and type of
transducers and different beam directions required to identify all the reference features in the calibration piece.
Such an installation may have five or more ultrasonic transducers suitably arranged (e.g. Figure 2).
Other arrangements of transducers may be possible provided that longitudinal and transverse defects can be
detected.
Key
L1, L2 longitudinal transducers
T1, T2 transverse transducers
W wall thickness transducer
Figure 2 — Examples of the arrangement of transducers
8 © ISO 2005 – All rights reserved

Any ultrasonic method (e.g. the pulse echo, guided wave) that demonstrates the ability to detect defects and
to measure wall thickness shall be used. The most common techniques used today are the contact or the
immersion type. Other techniques may be used. See Figure 3 as an example.

Key
1 transducers
2 cylinder
a
Water.
Figure 3 — Examples of coupling techniques
The cylinder wall shall be examined using UE transducers capable of detecting the specified calibration
notches. The examination shall cover longitudinal defects in both circumferential directions (clockwise and
counter clockwise) and transverse defects in both longitudinal directions (forward and backward) and consider
these defects to be located on the internal and external surfaces.
The cylinder wall shall be examined using UE transducers capable of detecting the specified minimum
guaranteed wall thickness using a normal transducer (angle of refraction 0°). The accuracy of the system shall
be ±5 % or ±0,1 mm, whichever is greater. The inaccuracy shall be taken into account when verifying the wall
thickness.
The cylinders to be examined and the search unit with the transducers shall go through a rotating motion and
translation relative to one another. The speeds of translation and rotation shall not exceed the speed used
during calibration.
The ultrasonic examination unit shall have a screen capable of depicting the various defects present in the
calibration cylinder. The installation shall have an automatic alarm when a fault signal (defect or below-
minimum guaranteed wall thickness) is registered that alerts the operator for each transducer to ensure that
its accuracy is maintained. See Figure 4.
A distinction in the defect detection between internal and external flaws shall be possible.
Key
T1 transverse transducer
1 screen
2 calibration specimen wall
3 ultrasonic examination signal trace from calibration specimen wall
4 inner reference notch
5 ultrasonic examination signal trace from inner reference notch
6 outer reference notch
7 ultrasonic examination signal trace from outer reference notch
8 alarm level
Figure 4 — Flaw alarm examples
11.4.3.3 Manual ultrasonic unit
The requirements in 11.4.3.2 shall apply as appropriate for the selection of the transducers and servicing of
the unit.
11.4.3.4 Cylinders
The outer and inner surfaces of any cylinder to be examined ultrasonically shall be in a suitable condition for
an accurate and reproducible test. In particular, the external surface shall be free of corrosion, non-adhering
paint, dirt and oil. An ultrasonic examination is only meaningful when the noise signals caused by the surface
are at least 50 % below the corresponding reference signal.
11.4.3.5 Personnel
The examination equipment shall be operated and its operation supervised by qualified and experienced
personnel only, as defined in ISO 9712. The tester may be certified to ISO 9712 Level I for ultrasonic
examination; however, the Level I operator shall be supervised by a Level II operator. The testing organization
shall retain a Level III operator (company employee or a third party) to oversee the entire ultrasonic
examination programme.
10 © ISO 2005 – All rights reserved

11.4.4 Calibration
11.4.4.1 General
Calibration of the UE defect examination and wall thickness measurement shall use a calibration specimen
with notches. A specimen of convenient length shall be prepared from a cylinder representative of the cylinder
to be tested with the same nominal diameter, wall thickness, external surface finish and material with similar
acoustic properties as the cylinder under test. The standard reference (reference cylinder or calibration
cylinder) shall have a known minimum guaranteed wall thickness (t ) that is less than or equal to the cylinder
m
under test.
11.4.4.2 Defect detection
11.4.4.2.1 UE notch requirements and dimensions
For manual and mechanized defect examination purposes, a minimum of four rectangular notches are
required as reference notches in the calibration specimen, (see e.g. Figure 5). The notches can be produced
either by means of electrical erosion or sawing, or by machining. The bottom corners of the notch may be
rounded. The notches shall be located such that there is no interference from any other defect in the reference
standard. The form and dimensions of the reference standard shall be verified. The four notches shall be as
follows:
 inner notch in longitudinal direction;
 inner notch in transverse direction;
 outer notch in longitudinal direction;
 outer notch in transverse direction.
They shall have the following dimensions in each case:
Length L: 50 mm;
Depth D: less than or equal to 10 % of actual measured wall thickness S of the calibration piece located
in the sidewall at a location that does not exceed 115 % of the minimum guaranteed wall
thickness with an absolute minimum of 0,2 mm and an absolute maximum of 2 mm;
Width W: u 2 D.
Key
1 outer notch
2 inner notch
L length of notches: 50 mm
D depth of notches: u 10 % S
W width of notches: u 2D
t actual measured wall thickness
a
Figure 5 — Examples of reference notches
11.4.4.2.2 Internal inspection notch requirements
When using ultrasonic examination in lieu of an internal visual inspection as specified in Clause 8, one of the
following reference notch groupings shall be required.
 Internal longitudinal and transverse reference notches with the dimensions as previously specified, except
that the depth shall be (5 ± 1) % of the minimum guaranteed wall thickness.
 10 % internal longitudinal and transverse reference notches with the dimensions as previously specified
for the four notches and a flat bottom hole (FBH) with a depth of one-third of the minimum guaranteed
wall thickness and a diameter less than or equal to 2 times the minimum guaranteed wall thickness (see
Figure 6).
12 © ISO 2005 – All rights reserved

Key
1 FBH
Figure 6 — Typical flat bottom hole (FBH) notch
11.4.4.2.3 Calibration procedures
During the calibration procedure, the ultrasonic examination equipment shall be adjusted in such a way that
the amplitude of the echoes from the reference notches equals the alarm level (see e.g. Figure 7). This alarm
level shall be set to at least 50 % of the screen height. On automated systems, this step shall be performed
dynamically. This sensitivity is the reference sensitivity.

Key
1 alarm level
2 signal of reference notch
Figure 7 — Reference notch amplitude
11.4.4.3 Wall thickness
To calibrate the manual and mechanized wall thickness measurement, a local thin area (LTA) with a diameter
equal to at least 2 times the effective beam width at the point of entrance on the calibration specimen shall be
used, the exact wall thickness being known.
The minimum guaranteed wall thickness of the gas cylinder known from the type approval is set as the alarm
level in the evaluation unit of the ultrasonic wall thickness measuring device.
11.4.4.4 Frequency of calibration
The UE equipment shall be calibrated at least at the beginning and at the end of each operator shift,
regardless of length, and any time equipment is changed (e.g. change of transducer). Calibration shall also be
undertaken at the end of operations that are of a duration less than that of a normal shift. If, during the
calibration, the presence of the respective reference notch is not detected, all cylinders examined
subsequently to the last acceptable calibration shall be re-examined after the equipment has been
recalibrated.
11.4.5 Performance of the examination
11.4.5.1 Defect detection in cylindrical part by automated installation
The cylindrical part of the cylinder and the transitions to the shoulder and to the base shall be examined for
longitudinal and transverse defects using an automated examination device.
The pulse repetition rate of the transducers, rotational speed of the cylinder, and axial speed of the scanning
head shall be mutually adjusted in such a way that the system is capable of locating all of the calibration flaws.
At no time shall the speeds used during calibration be exceeded during the examination. It shall be ensured
that the system provides 100 % coverage of the surface being examined. When applicable, e.g. a helix-based
system, at least 10 % overlap shall be guaranteed.
11.4.5.2 Wall thickness measurement by automated installation
The cylindrical part shall be examined 100 % for wall thinning.
11.4.6 Interpretation of results
Gas cylinders examined to the examination sensitivity in accordance with 11.4.4.2 and 11.4.4.3 where no
defect signal above the alarm level has been recorded have passed the examination. Where a defect signal
above the alarm level (defect or below minimum guaranteed wall thickness) has been recorded (see e.g.
Figure 8), the cylinder shall be re-evaluated in accordance with Annex B or scrapped.

Key
T2 transverse transducer
1 screen
2 cylinder wall
3 ultrasonic examination signal from cylinder wall
4 crack on internal surface
5 ultrasonic examination signal from crack
6 region of signals from cracks on internal surface
7 region of signals from cracks on external surface
8 alarm level
Figure 8 — Detection of crack in transverse direction
14 © ISO 2005 – All rights reserved

11.4.7 Records
In addition to the required records as specified in 14.7, the following information shall be recorded.
a) Identification of ultrasonic equipment used.
b) Serial number or unique identification of the calibration cylinder used.
c) Ultrasonic examination symbol.
d) Results of examination. If subsequent evaluation according to 11.4.6 and Annex B requalify the cylinder,
the basis of requalification shall be recorded.
12 Inspection of valve and other accessories
If a valve or any other accessory is to be reintroduced into service, it shall be inspected and maintained to
ensure that it will perform satisfactorily in service and meet the requirements of gas tightness from valve
manufacturing standards, e.g. ISO 10297. An example of a suitable method is given in Annex F.
13 Cylinder repairs
Any operation that could result in loss of wall thickness to below minimum guaranteed wall thickness shall be
completed before the inspection and testing procedure (see Annex B).
14 Final operations
14.1 Preparation for change of service
When the cylinder is being prepared for final identification for future service, it shall be ensured that any
residual gas in the container is compatible with the new gas service (see Clause 6 for depressurization
requirements and ISO 11621).
14.2 Drying, cleaning, painting and coating
14.2.1 Drying and cleaning
The interior of each acceptable (passed) cylinder shall be thoroughly dried by a suitable method immediately
after hydraulic pressure testing so there is no trace of free water (see 14.2.2 for maximum temperature values
to be used, if applicable). The interior of the cylinder shall be inspected to ensure that it is dry and free from
other contaminants.
14.2.2 Painting and coating
Cylinders are sometimes repainted using paints that require stoving. Plastic coatings may also be reapplied.
Paint and coating shall be applied so that all cylinder markings remain legible.
Aluminium-alloy cylinders are normally manufactured using precise heat treatment to obtain the final
mechanical properties of the cylinders. Therefore the maximum temperature for any operation shall be limited.
In no case shall the temperature of the cylinder exceed that recommended by the manufacturer since
overheating could change the mechanical properties of the cylinder.
Cylinders manufactured from heat-treatable aluminium alloys shall not be heated to temperatures exceeding
175 °C unless the cylinder manufacturer recommends otherwise. Only responsible organizations that can
properly control heat input and record time and temperature shall heat cylinders. The total cumulative time at
temperatures between 110 °C and 175 °C shall be limited to the time recommended by the cylinder
manufacturer. Cylinders heated in accordance with these provisions shall not require further testing.
Unless otherwise recommended by the cylinder manufacturer, for cylinders manufactured from non-heat-
treated alloys (e.g. AA5283), the maximum temperature shall not exceed 80 °C. For temperatures between
70 °C and 80 °C, the exposure time shall be limited to 30 min. If the heat exposure time exceeds 30 min at
temperatures greater than or equal to 70 °C, or if at any time the temperature exceeds 80 °C, then agreement
shall be obtained from the manufacturer regarding further use of the cylinder.
14.3 Re-valving of the cylinder
Before re-valving the cylinder, the thread type shall be identified. The appropriate valve shall be fitted to the
cylinder using a suitable sealing material. An optimum torque necessary both to ensure a seal between the
valve and the cylinder and to prevent over-stressing the neck shall be used as specified in ISO 13341.
The torque applied shall take into consideration the size and form of the threads, the material of the valve and
the type of sealing material used according to the manufacturer's recommendations. Where the use of
lubricants/sealing material is permitted, only those approved for the gas service shall be used, taking
particular care for oxygen service (see ISO 11114-2).
14.4 Check on cylinder tare
The requirement shall apply only to cylinders for liquefied gases. However, it may be applied to any cylinder
when there is doubt. The tare of the cylinders shall b
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