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SEMI C6.7-93 © SEMI 1993, 2002 2 3.2 Averaged Observed Concentration (XB, XM, XN) B X = SUM(X Bi )/N B M X = SUM(X Mi )/N M N X = SUM(X Ni )/N N 3.3 Calcul ate concentration (X P , X Q ) X P = M X – B X X Q = N X – B X 3…

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SEMI C6.7-93 © SEMI 1993, 2002 1
SEMI C6.7-93 (Reapproved 1102)
PARTICLE SPECIFICATION FOR GRADE 10/0.2 NITROGEN IN HIGH
PRESSURE GAS CYLINDERS
This specification was technically approved by the Global Gases Committee and is the direct responsibility of
the North American Gases Committee. Current edition approved by the North American Regional Standards
Committee on July 21, 2002. Initially available at www.semi.org October 2002; to be published November
2002. Originally published in 1993.
1 Purpose
1.1 The purposes of this document are (1) to set a
maximum permissible particle concentration for 10/0.2
grade cylinder nitrogen, and (2) to describe a reference
method for its verification.
2 Scope
2.1 This specification applies to nitrogen contained in
high pressure gas cylinders; it is not applicable to
pipeline gases.
2.2 A nitrogen cylinder consists of three components:
(1) a cylinder bottle, (2) compressed nitrogen contained
within, and (3) a cylinder valve. Each component can
be a particle source. This specification applied to the
total number of particles detected in the gas as obtained
from the cylinder under a prescribed condition. No
consideration is given to the origin of the particles.
2.3 It is known that pressure reduction, if not
controlled, can produce a large number of artifact
particles through nucleation and condensation. To avoid
this complication, this specification adopts particle
counters that can be operated at a pressure up to 200 bar
(3000 psi), eliminating the need for pressure reduction
and its associated problems.
2.4 It is known that particle content in cylinder gases
varies with time because particles can be lost to
cylinder walls by diffusion or sedimentation, and
detached from cylinder walls by flow pulses or
mechanical shocks. It is important to measure particle
concentration under the worst conditions which
represent typical handling of gas cylinders. This
specification describes a standard shock test that fulfills
the above requirements and provides a procedure to
count particles immediately after the shock.
2.5 If this test method is to be used for more than one
cylinder, then each cylinder must be tested. It is known
that particle contamination in cylinder gases is a strong
function of the handling history of the individual
cylinders. Cylinders in the same batch of filling are
usually returned from various customers after various
periods of service. Uniform quality can not be assumed
for the same batch of cylinders unless each of them has
gone through a dedicated process that erases the
memory of previous history prior to filling. Therefore,
batch sampling at 10% or 20% cannot be accepted
because of the significant differences among cylinders.
2.6 The requirement of 100% sampling restricts the
total amount of gas in each cylinder that can be used for
sampling purposes. This restriction, in turn, calls for
certain relaxation of the statistical requirement for
particle sampling at low concentration levels.
2.7 This standard does not purport to address safety
issues, if any, associated with its use. It is the
responsibility of the users of this standard to establish
appropriate safety health practices and determine the
applicability or regulatory limitations prior to use.
3 Terminology
3.1 Variables
X
Bi
= Observed particle concentration in the i
th
sample
interval of the background
X
Mi
= Observed particle concentration in the i
th
sample
interval before shocks
X
Ni
= Observed particle concentration in the i
th
sample after
shocks
N
B
= Number of sample intervals of the background
N
M
= Number of sample intervals before shocks
N
N
= Number of sample intervals after shocks
B
X=
Averaged observed particle concentration of the
background
M
X=
Averaged observed particle concentration before
shocks
N
X=
Averaged observed particle concentration after
shocks
X
P
= Calculated particle concentration before shocks
X
Q
= Calculated particle concentration after shocks
S
B
=
Standard deviation of
B
X
S
M
=
Standard deviation of
M
X
S
N
=
Standard deviation of
N
X
SE
P
= Standard deviation of X
P
SE
Q
= Standard deviation of X
Q
SEMI C6.7-93 © SEMI 1993, 2002 2
3.2 Averaged Observed Concentration (XB, XM, XN)
B
X
= SUM(X
Bi
)/N
B
M
X = SUM(X
Mi
)/N
M
N
X = SUM(X
Ni
)/N
N
3.3 Calculate concentration (X
P
, X
Q
)
X
P
=
M
X –
B
X
X
Q
=
N
X –
B
X
3.4 Standard Deviation (S
B
, S
M
, S
N
)
S
B
= [SUM(X
Bi
–
B
X )
2
/N
B
– 1)]
1/2
S
M
= [SUM(X
Mi
–
M
X )2/(N
M
– 1)]
1/2
S
N
= [SUM(X
Ni
–
N
X )2/(N
N
– 1)]
1/2
3.5 Standard Error (SE
P
,SE
Q
)
SE
P
= [(S
M
2/N
M
) + (S
B
2/N
B
)]
1/2
SE
Q
= [(S
N
2/N
N
) + (S
B
2/N
B
)]
1/2
4 Apparatus
4.1 High-Pressure Particle Counter (HPC) — An
instrument capable of counting particles in compressed
gaseous nitrogen at a pressure up to 200 bar (3000 psi),
having a minimum counting efficiency of 50% at 0.2
µm and reaching 100% at 0.25 µm. This value is
determined at ambient pressure by the instrument
manufacturer using 0.2 µm monodisperse particles and
a reference counter with a proven counting efficiency of
100% at 0.2 µm. Note that the nominal flow rate of the
HPC is fixed at any pressure but the sample flow rate
should be adjusted to within 5% of the manufacturer’s
specified flow rate, for the pressure and reported its
equivalent standard flow rate at ambient pressure (1
bar).
4.2 Impact Shock Device — A device that can
reproducibly impart an impact shock of 10
4
m/sec
2
with
a 10% tolerance to a gas cylinder. A convenient set up
as shown in Figure 1 can be used. A steel ball is
attached to a chain with the other end fastened to the
test cylinder. The ball is lifted to form a 90° angle with
the cylinder, is released to follow a 90° free fall arc, and
strikes the test cylinder. The desired ball mass and
chain length are to be determined by monitoring the
corresponding shock intensity by an accelerometer. For
a typical 44 liter cylinder, a ball mass of 160 gm and a
chain length of 60 cm can produce the desired impact
shock.
5 Test Method
5.1 Determine the averaged background concentration
(
B
X ) by passing particle-free, compressed nitrogen
through the HPC. Count a minimum of 5 sample
intervals, each of at least 6 standard liters (0.2 SCF) or
taken over a time period of 6 minutes, whichever is
greater. A high purity gas filter can be used to remove
particles greater than 0.2 µm. Calculate
B
X as defined
in Section 3.
B
X must not exceed 1 particle per 30
second liters.
5.2 Set up the experimental apparatus as shown in
Figure 2. Directly connect the test cylinder to a High-
pressure Particle Counter (HPC), a pressure gauge, and
a Flow Control Device (FCD). Note that NO
REGULATOR is used before the HPC. The sampling
line should be clean and as short as possible. The flow
control device can be a metering valve and a flowmeter
or a critical orifice.
5.3 Determine
M
X by opening the cylinder valve and
count the particles for at least 5 sample intervals, each
of at least 6 standard liters (0.2 SCF) or taken over a
time of 6 minutes, whichever is greater. Calculate X
P
and SE
P
as defined in Section 3.
5.4 Apply 4 impact shocks of approximately 10
4
m/sec
2
each, 10 sec apart, to the bare surface of the test
cylinder. Each shock whould be applied at the
approximate vertical midpoint of the cylinder; the four
shocks should be separated from each other by
approximately 90° circumferentially.
5.5 Determine
N
X by counting the particles after the
shocks for at least 5 sample intervals, each of at least 6
standard liters (0.2 SCF) or taken over a time of 6
minutes, whichever is greater. The sampling should be
completed within 2 hours after the shocks. Calculate X
Q
and SE
Q
as defined in Section 3.
6 Specification
6.1 Maximum Permissible Particle Concentration —
10 particles per 30 standard liters.
6.2 The specification will be considered met if the
calculated concentration of particles plus two standard
errors does not exceed 10 particles per 30 standard
liters for both measurements before and after the impact
shocks, i.e.:
X
P
+ 2SE
P
≤ 10 particles/30 standard liters
and
X
Q
+ 2SE
Q
≤ 10 particles/30 standard liters
SEMI C6.7-93 © SEMI 1993, 2002 3
7 Report
The report shall contain the value of the measured
sample volumes, values of all the variables defined in
Section 3, the mass of the steel ball, and length of the
chain.
Figure 1
Figure 2
NOTICE: SEMI makes no warranties or
representations as to the suitability of the standards set
forth herein for any particular application. The
determination of the suitability of the standard is solely
the responsibility of the user. Users are cautioned to
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product data sheets, and other relevant literature
respecting any materials mentioned herein. These
standards are subject to change without notice.
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takes no position respecting the validity of any patent
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