ISO 6406:2005

INTERNATIONAL ISO
STANDARD 6406
Second edition
2005-02-01
Gas cylinders — Seamless steel gas
cylinders — Periodic inspection and
testing
Bouteilles à gaz — Bouteilles à gaz en acier sans soudure — Contrôles
et essais périodiques
Reference number
©
ISO 2005
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ii © ISO 2005 – All rights reserved

Contents Page
Foreword. iv
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. 3
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.16
13 Replacement of cylinder parts. 16
14 Cylinder repairs. 16
15 Final operations . 18
16 Rejection and rendering cylinder unserviceable. 20
Annex A (informative) Periodic inspection and test periods . 21
Annex B (normative) Description, evaluation of defects and conditions for rejection of seamless
steel gas cylinders at the time of visual inspection . 22
Annex C (informative) List of gases corrosive to cylinder material. 27
Annex D (normative) Procedure to be adopted when de-valving and/or when it is suspected that a
cylinder valve is obstructed. 28
Annex E (informative) Volumetric expansion testing of gas cylinders. 31
Annex F (informative) Inspection and maintenance of valves and their junctions —
Recommended procedures. 39
Annex G (informative) Test date rings for gas cylinders. 40
Bibliography . 41

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 6406 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 6406:1992), which has been technically revised.

iv © ISO 2005 – All rights reserved

INTERNATIONAL STANDARD ISO 6406:2005(E)

Gas cylinders — Seamless steel gas cylinders — Periodic
inspection and testing
1 Scope
This International Standard deals with seamless steel transportable gas cylinders (single or those that
comprise a bundle) intended for compressed and liquefied gases under pressure, of water capacity from 0,5 l
up 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 to be re-introduced into service for a further period of time.
This International Standard does not apply to periodic inspection and testing of acetylene cylinders or
composite cylinders with steel 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.
1)
ISO 9712:— , Non-destructive testing — Qualification and certification of personnel
ISO 11114-1:1997, Transportable gas cylinders — Compatibility of cylinder and valve materials with gas
contents — Part 1: 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 periodic inspection and test on its first receipt of a filler following the expiry of the
interval established 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 Annex A).
Provided the cylinder has been subjected to normal conditions of use and has not been subjected to abusive
and abnormal conditions that would render 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.
1) To be published. (Revision of ISO 9712:1999)
It is the responsibility of the owner or user to submit the cylinder for 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 inspection and tests (Clause 5);
b) depressurization and de-valving (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) replacement of cylinder parts (Clause 13);
j) cylinder repairs (Clause 14);
k) final operations (Clause 15);
l) rejection and rendering cylinder unserviceable (Clause 16).
It is recommended that the procedures a) to l) be performed in the sequence listed. In particular, the check of
internal condition [d)] should be carried out before the pressure test or before the ultrasonic examination [g)].
Cylinders that fail an inspection or test shall be rejected (see Clause 16). Where a cylinder passes the above-
listed procedures but 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 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 steel cylinders may be affected by heat exposure. Therefore, the maximum
temperature for any operation shall be limited in accordance with the manufacturer's recommendation.
5 Identification of cylinder and preparation for inspections and tests
Before any work is carried out, the relevant cylinder data and its contents and ownership shall be identified
(e.g. from the labelling and stamping, see ISO 13769). Cylinders with incorrect or illegible markings or
unknown gas contents shall be set aside for special handling.
If the contents are identified as hydrogen or other embrittling gas, only those cylinders manufactured or
qualified as hydrogen cylinders shall be used for that service. It shall be checked that the cylinder is
2 © ISO 2005 – All rights reserved

compatible for hydrogen service, i.e. with respect to the maximum tensile strength and internal surface
condition. Cylinders in accordance with ISO 13769 are stamped “H”.
All other cylinders shall be withdrawn from hydrogen service and their suitability for their new, intended service
checked (see ISO 11621).
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 investigate further (see 11.4)
6.2 Cylinders requiring depressurization
Cylinders shall be depressurized and emptied 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. See Annex C.
Before removing any pressure retaining accessory, e.g. valve, flange, etc., a positive check shall be
performed to ensure that the cylinder does not contain any gas under pressure. This may be performed as
described in Annex D using the device such as shown in Figure D.1.
Cylinders with inoperative or blocked valves shall be treated as outlined in Annex D.
Similarly, in the case of cylinders disassembled from bundles and not equipped with cylinder valves, the
connecting “T”-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 D.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 to below 5 bar before ultrasonic examination. For cylinders under inspection
by the ultrasonic method, see 11.4.
7 External visual inspection
7.1 Preparation for external visual inspection
When necessary, 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. by brushing, shot-blasting (under
closely controlled conditions), water jet abrasive cleaning, chemical cleaning or other suitable methods. 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 proper inspection, then the coating shall be stripped. If the coating has been removed by the
application of heat, in no case shall the temperature of the cylinder have exceeded 300 °C.
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 (see Table B.1);
c) corrosion (see Table B.2). Special attention shall be given to areas where water may 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;
d) other defects such as illegible, incorrect or unauthorized stamp markings, or unauthorized additions or
modifications;
e) integrity of all permanent attachments (see B.2);
f) vertical stability, if relevant (see Table B.1).
For rejection criteria, see Annex B. Cylinders no longer suitable for future service shall be rendered
unserviceable (see Clause 16).
8 Check of internal condition
Cylinders shall be inspected internally in order to complete periodic inspection and testing requirements. For
cylinders under examination 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. Otherwise, each cylinder
shall be inspected internally using adequate illumination 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 no risks to the tester while
performing the 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 under closely controlled conditions by shot-blasting, water jet abrasive
cleaning, flailing, steam jet, hot water jet, rumbling, chemical cleaning or other suitable method. 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 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,
alternative methods may be substituted for the internal visual inspection.
These are:
 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. rust from the water used after the hydraulic test. If rust 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. Only when all doubts are eliminated may the cylinder be further processed (see Annex B).
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. 25E) and to ensure that they are
 clean and of full form;
 free of damage;
 free of burrs;
 free of cracks;
 free of other imperfections.
Cracks manifest themselves as lines that run vertically down the thread and across the thread faces. They
should not be confused with tap marks (thread machining stop marks). Special attention should be paid to the
area at the bottom of the threads.
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 or the thread type changed to provide the appropriate number of
effective threads. After re-tapping or changing the thread form, 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 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 (see Clause 16).
11 Pressure test or ultrasonic examination
11.1 General
Each cylinder shall be submitted for either a pressure test or an ultrasonic examination.
WARNING — Appropriate measures shall be taken to ensure safe operation and to contain any energy
that may be 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 results shall be final. The
test pressure shall be in accordance with the stamp markings on 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 General
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 pipework, 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 × the maximum test pressure of
any cylinder that may be tested.
11.2.2.2 Pressure gauges shall be of 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 at least once a month. The master gauge shall be calibrated in
accordance with national requirements. The pressure gauge shall be chosen so 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 given in 11.2.3.3.
11.2.3 Test criteria
11.2.3.1 More than one cylinder at a time may be tested provided that they 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 less than 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.
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 an 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.
6 © ISO 2005 – All rights reserved

11.3 Hydraulic volumetric expansion test
Annex E proposes typical methods for carrying out this test and gives details for determining the volumetric
expansion of seamless steel 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 weighing bowl. Care shall be taken that the entire external surface of the cylinder is wet
without the presence of 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 of gas cylinders as described below is based on the ultrasonic examination of
pipes in accordance with 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 steel gas cylinders (water capacity W 2 I) within the framework of
periodic inspections may be carried out in lieu of the tests described 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).
When such an examination device is not able to do this outside the cylindrical section, a supplementary
manual examination shall be performed (see Figure 2).
Cylinders that are suspected of fire or heat damage shall not be examined ultrasonically.
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 inspection 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 3).
Other arrangements of transducers may be possible provided that longitudinal and transverse defects can be
detected.
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 4 as an example.
Key
1 UE transducers, moving
2 ultrasonic examination equipment
3 cylinder movement
Figure 1 — Examples of two types of ultrasonic examination devices for gas cylinders

Key
L longitudinal of the base shape
T transverse of the base shape
„ manual (common practice)
† automated (common practice)
Figure 2 — Defect detection in cylinder ends with foot-rings

8 © ISO 2005 – All rights reserved

Key
L1, L2 longitudinal transducers
T1, T2 transverse transducers
w wall thickness transducer
Figure 3 — Examples of the arrangement of transducers

Key
1 transducers
2 cylinder
a
Water.
Figure 4 — 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
anti-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 of each transducer to ensure that its
accuracy is maintained. See Figure 5.
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 UE signal trace from calibration specimen wall
4 inner reference notch
5 UE signal trace from inner reference notch
6 outer reference notch
7 UE signal trace from outer reference notch
8 alarm level
Figure 5 — Flaw alarm examples
10 © ISO 2005 – All rights reserved

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 external and internal 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 by, 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.
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, e.g. all steels. The standard reference (reference cylinder or
calibration cylinder) shall have a known minimum guaranteed wall thickness, t , that is less than or equal to
g
the cylinder under test.
11.4.4.2 Defect detection
11.4.4.2.1 UE notch requirements and dimensions
For manual and automated defect examination purposes, a minimum of four rectangular notches is required
as reference notches in the calibration specimen (see Figure 6). 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;
with the following dimensions in each case:
 length, L: 50 mm;
 depth, D: for cylinders with actual tensile strength W 950 MPa or cylinders intended to contain embrittling
gases (see ISO 11114-1), depth D u (5 ± 1) % actual measured wall thickness, t , of the calibration piece
a
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 1 mm;
 depth, D: for cylinders with actual tensile strength < 950 MPa and not intended to contain embrittling
gases, depth D u 10 % of actual measured wall thickness, t , of the calibration piece located in the
a
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 1 mm;
 width, W: u 2 D.
Key
1 outer notch
2 inner notch
L length of notches: 50 mm
D depth of the notches: u (5 ± 1) % t or u 10 % t
g a
W width of the notches: u 2D
t actual measured wall thickness
a
Figure 6 — Examples of reference notches

12 © ISO 2005 – All rights reserved

When a 10 % sidewall notch criterion is used, a fifth inner transverse transition notch is required to examine
the sidewall-to-base transition (SBT) region. The fifth notch shall have the same dimensions of width and
length as the previously described four notches with the notch depth (10 ± 1) % of minimum calculated wall
thickness (see Figure 7).
Key
1 approximate notch location
NOTE Notch depth (10 ± 1) % of minimum calculated wall thickness t .
c
Figure 7 — Sidewall-to-base transition (SBT) region

11.4.4.2.2 Internal inspection notch requirements
When using ultrasonic examination for internal inspection, one of the following calibration reference notch
groupings shall be required:
 5 % internal longitudinal and transverse reference notches with dimensions as previously specified for the
four notches. When this notch criterion is selected as part of commissioning the system, it shall be
confirmed on one typical specimen that the system is capable of detecting a (10 ± 1) % SBT notch
(see Figure 7); or
 10 % internal longitudinal and transverse reference notches with dimensions as previously specified for
the four notches, a fifth SBT notch (see Figure 7) with previously specified dimensions, as well as a flat
bottom hole (FBH) with a depth of 1/3 minimum guaranteed wall thickness and a diameter less than or
equal to × 2 minimum guaranteed wall thickness (see Figure 8).

Key
1 FBH
Figure 8 — 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 (e.g. Figure 9). 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 9 — Reference notch amplitude
For screening gas cylinders that previously have not been ultrasonically examined and that contain embrittling
gases (see ISO 11114-1), the ultrasonic sensitivity may be increased by 6 dB provided the system is first
calibrated against the reference feature used for the acceptance criteria to establish the basic sensitivity
(e.g. Figure 10). Cylinders failing this screening examination shall require further investigation or shall be
rendered unserviceable.
14 © ISO 2005 – All rights reserved

Key
1 alarm level
2 signal of adjusted reference notch
Figure 10 — Screening test amplitude
11.4.4.3 Wall thickness
To calibrate the manual and automated wall thickness measurement, a local thin area (LTA) with a diameter
equal to at least × 2 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 when any timing 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 must be re-examined after the equipment has been
recalibrated.
11.4.5 Performing the examination
11.4.5.1 Defect detection in cylindrical section by automated installation
The cylindrical section of the cylinder and the transitions to the shoulder and to the base shall be examined for
longitudinal and transverse defects using an automatic 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. Ensure 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. Figure 7 shows notch placement for examination of an SBT.
11.4.5.2 Defect detection in cylinder ends for cylinders with foot-rings
In the case of cylinders with foot-rings, the critical area in the transition zone shall be checked taking into
account the accessibility of the test surface and the roughness of the external surface (see Figure 2).
11.4.5.3 Wall thickness measurement by automated installation
The cylindrical section shall be examined 100 % for wall thinning.
11.4.5.4 Base thickness measurements by manual testing
Only for cylinders with convex bases (see Figure 11), the thickness of the base at the centre shall be
measured manually with a normal ultrasonic transducer if UE has not already been performed using automatic
devices. This measurement shall be greater than or equal to the minimum guaranteed sidewall thickness for
shapes A and B in Figure 11 and greater than or equal to × 1,5 the minimum guaranteed sidewall thickness
for shapes C and D.
The thickness, b, at the centre of a convex end shall be not less than that required by the following criteria
where the inside knuckle radius, r, is not less than 0,075 D:
b W 1,5 t for 0,40 > H/D W 0,20
c
b W t for H/D W 0,40
c
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
(e.g. Figure 12), the cylinder shall be re-evaluated in accordance with Annex B or scrapped.
11.4.7 Records
In addition to the required records as specified in 15.7, 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 in accordance with 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, see, e.g. ISO 10297. An example of a suitable method is given in Annex F.
13 Replacement of cylinder parts
Replacement of foot-rings and neck-rings or the grinding of cuts and other imperfections may be carried out.
All operations involving the application of heat shall conform to the heat limits given in 15.1. All corrosion
products shall be removed prior to repair.
NOTE When a neck-ring and/or foot-ring is replaced, the empty weight of the cylinder may change.
14 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).
16 © ISO 2005 – All rights reserved

Key
1 cylindrical section
Figure 11 — Convex base ends
Key
T2 transverse transducer
1 screen
2 cylinder wall
3 UE signal from cylinder wall
4 crack on internal surface
5 UE 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 12 — Example of detection of crack in transverse direction
15 Final operations
15.1 Drying, cleaning and painting
15.1.1 Drying and cleaning
The interior of each cylinder shall be thoroughly dried by a suitable method, at a temperature not exceeding
300 °C, immediately after hydraulic pressure testing, so that there is no trace of free water. The interior of the
cylinder shall be inspected to ensure that it is dry and free from other contaminants.
15.1.2 Painting and coating
Cylinders are sometimes repainted using paints that require stoving. Plastic coatings may also be re-applied.
Paint or coating shall be applied in such a way that markings stamped on the cylinder remain legible.
In no case shall the temperature of the cylinder exceed 300 °C since overheating could change the
mechanical properties of the cylinder.
15.2 Re-valving of the cylinder
Before re-valving the cylinder, the thread type shall be identified. The appropriate valve shall be fitted in
accordance with ISO 13341.
15.3 Check on cylinder tare
This 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 be obtained by weighing on a scale calibrated with
traceability to national or international standards. The weighing scale shall be checked for accuracy on a daily
basis. The capacity of the weighing scale shall be suitable for the tare of the appropriate cylinders.
18 © ISO 2005 – All rights reserved

The tare is the sum of the empty weight plus the mass of any coating (e.g. paint) used in service, the mass of
the valve including dip tube where fitted, any fixed valve guard and the mass of all other parts that are
permanently attached (e.g. by clamping or bolting) to the cylinder when presented for filling. If the tare of the
cylinder differs from the stamped tare by more than the value shown in Table 1 and this is not due to reasons of
damage, the original tare shall be cancelled. The ne
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