This special provision applies to periodic inspection and test of over-moulded cylinders as defined in 1.2.1.

Over-moulded cylinders subject to 6.2.3.5.3.1 shall be subject to periodic inspection and test in accordance with 6.2.1.6.1, adapted by the following alternative method:
- Substitute test required in 6.2.1.6.1 d) by alternative destructive tests;
- Perform specific additional destructive tests related to the characteristics of over-moulded cylinders.

The procedures and requirements of this alternative method are described below.

Alternative method:

(a) General
The following provisions apply to over-moulded cylinders produced serially and based on welded steel cylinder shells in accordance with EN 1442:2017, EN 14140:2014 + AC:2015 or annex I, parts 1 to 3 to Council Directive 84/527/EEC. The design of the over-moulding shall prevent water from penetrating on to the inner steel cylinder shell. The conversion of the steel cylinder shell to an over-moulded cylinder shall comply with the relevant requirements of EN 1442:2017 and EN 14140:2014 + AC:2015.

Over-moulded cylinders shall be equipped with self-closing valves.

(b) Basic population
A basic population of over-moulded cylinders is defined as the production of cylinders from only one over-moulding manufacturer using new inner steel cylinder shells manufactured by only one manufacturer within one calendar year, based on the same design type, the same materials and production processes. 

(c) Sub-groups of a basic population
Within the above defined basic population, over-moulded cylinders belonging to different owners shall be separated into specific sub-groups, one per owner.

If the whole basic population is owned by one owner, the sub-group equals the basic population.

(d) Traceability
Inner steel cylinder shell marks in accordance with 6.2.3.9 shall be repeated on the over-moulding. In addition, each over-moulded cylinder shall be fitted with an individual resilient electronic identification device. The detailed characteristics of the over-moulded cylinders shall be recorded by the owner in a central database. The database shall be used to:
- Identify the specific sub-group;
- Make available to inspection bodies, filling centres and competent authorities the specific technical characteristics of the cylinders consisting of at least the following: serial number, steel cylinder shell production batch, over-moulding production batch, date of over-moulding;
- Identify the cylinder by linking the electronic device to the database with the serial number;
- Check individual cylinder history and determine measures (e.g. filling, sampling, retesting, withdrawal);
- Record performed measures including the date and the address of where it was done.

The recorded data shall be kept available by the owner of the over-moulded cylinders for the entire life of the sub-group.

(e) Sampling for statistical assessment
The sampling shall be random among a sub-group as defined in sub-paragraph (c). The size of each sample per sub-group shall be in accordance with the Table in sub-paragraph (g).

(f) Test procedure for destructive testing
The inspection and test required by 6.2.1.6.1 shall be carried out except (d) which shall be substituted by the following test procedure:
- Burst test (according to EN 1442:2017 or EN 14140:2014 + AC:2015).

In addition, the following tests shall be performed:
- Adhesion test (according to EN 1442:2017 or EN 14140:2014 + AC:2015);
- Peeling and Corrosion tests (according to EN ISO 4628-3:2016).

Adhesion test, peeling and corrosion tests, and burst test shall be performed on each related sample according to the Table in sub-paragraph (g) and shall be conducted after the first 3 years in service and every 5 years thereafter.

(g) Statistical evaluation of test results - Method and minimum requirements
The procedure for statistical evaluation according to the related rejection criteria is described in the following.

+-----------+---------+--------------+-----------------+----------------------+
|   Test    | Type of |   Standard   |    Rejection    |  Sampling out of a   |
| interval  |  test   |              |     criteria    |      sub-group       |
|  (years)  |         |              |                 |                      |
+-----------+---------+--------------+-----------------+----------------------+
|  After 3  |  Burst  | EN 1442:2017 | Burst pressure  | 3 x third root of Q  |
| years in  |  test   |              | point of the    | or Q/200 whichever   |
|  servive  |         |              | representative  | is lower, and with a |
| (see (f)) |         |              | sample must be  | minimum of 20 per    |
|           |         |              | above the lower | sub-group (Q)        |
|           |         |              | limit of tole-  |                      |
|           |         |              | rance interval  |                      |
|           |         |              | on the Sample   |                      |
|           |         |              | Performance     |                      |
|           |         |              | Chart *)        |                      |
|           |         |              | No individual   |                      |
|           |         |              | test result     |                      |
|           |         |              | shall be less   |                      |
|           |         |              | than the test   |                      |
|           |         |              | pressure        |                      |
|           +---------+--------------+-----------------+----------------------+
|           | Peeling | EN ISO 4628- | Max corrosion   | Q/1000               |
|           |   and   | 3:2016       | grade: Ri2      |                      |
|           |  corro- |              |                 |                      |
|           |  sion   |              |                 |                      |
|           +---------+--------------+-----------------+----------------------+
|           |  Adhe-  | ISO 2859-    | Adhesion value  | See ISO 2859-1:1999  |
|           | sion of | 1:1999 +     | > 0.5 N/mm˛     | + A1:2011 applied to |
|           | Polyure-| A1:2011      |                 | Q/1000               |
|           | thane   | EN 1442:2017 |                 |                      |
|           |         | EN 14140:2014|                 |                      |
|           |         | + AC:2015    |                 |                      |
+-----------+---------+--------------+-----------------+----------------------+
|  Every 5  |  Burst  | EN 1442:2017 | Burst pressure  | 6 x third root of Q  |
|   years   |  test   |              | point of the    | or Q/100 whichever   |
| thereafter|         |              | representative  | is lower, and with a |
| (see (f)) |         |              | sample must be  | minimum of 40 per    |
|           |         |              | above the lower | sub-group (Q)        |
|           |         |              | limit of tole-  |                      |
|           |         |              | rance interval  |                      |
|           |         |              | on the Sample   |                      |
|           |         |              | Performance     |                      |
|           |         |              | Chart *)        |                      |
|           |         |              | No individual   |                      |
|           |         |              | test result     |                      |
|           |         |              | shall be less   |                      |
|           |         |              | than the test   |                      |
|           |         |              | pressure        |                      |
|           +---------+--------------+-----------------+----------------------+
|           | Peeling | EN ISO 4628- | Max corrosion   | Q/1000               |
|           |   and   | 3:2016       | grade: Ri2      |                      |
|           |  corro- |              |                 |                      |
|           |  sion   |              |                 |                      |
|           +---------+--------------+-----------------+----------------------+
|           |  Adhe-  | ISO 2859-    | Adhesion value  | See ISO 2859-1:1999  |
|           | sion of | 1:1999 +     | > 0.5 N/mm˛     | + A1:2011 applied to |
|           | Polyure-| A1:2011      |                 | Q/1000               |
|           | thane   | EN 1442:2017 |                 |                      |
|           |         | EN 14140:2014|                 |                      |
|           |         | + AC:2015    |                 |                      |
+-----------+---------+--------------+-----------------+----------------------+

*) Om >= 1 + Os x k3(n;p;1-alpha). In this and the subsequent formula, the "O" stands for the Greek capital letter Omega. Burst pressure point (BPP) of the representative sample is used for the evaluation of test results by using a Sample Performance Chart:

Step 1: Determination of the burst pressure point (BPP) of a representative sample

Each sample is represented by a point whose coordinates are the mean value of burst test results and the standard deviation of burst test results, each normalised to the relevant test pressure.

BPP: (Os = s / PH; Om = x / PH)

With

x = sample mean value;
s = sample standard deviation;
PH = test pressure

Step 2: Plotting on a Sample Performance Chart

Each BPP is plotted on a Sample Performance Chart with following axis:
- Abscissa: Standard Deviation normalised to test pressure (Os)
- Ordinate: Mean value normalised to test pressure (Om)

Step 3: Determination of the relevant lower limit of tolerance interval in the Sample Performance Chart

Results for burst pressure shall first be checked according to the Joint Test (multidirectional test) using a significance level of alpha = 0.05 (see paragraph 7 of ISO 5479:1997) to determine whether the distribution of results for each sample is normal or non-normal.
- For a normal distribution, the determination of the relevant lower limit of tolerance is given in step 3.1.
- For a non-normal distribution, the determination of the relevant lower limit of tolerance is given in step 3.2.

Step 3.1: Lower limit of tolerance interval for results following a normal distribution

In accordance with the standard ISO 16269-6:2014, and considering that the variance is unknown, the unilateral statistical tolerance interval shall be considered for a confidence level of 95% and a fraction of population equal to 99.9999%.

By application in the Sample Performance Chart, the lower limit of tolerance interval is represented by a line of constant survival rate defined by the formula:

Om = 1 + Os x k3(n;p;1-alpha)

with
k3 = factor function of n, p and 1-alpha;
p = proportion of the population selected for the tolerance interval (99.9999%);
1-alpha = confidence level (95%);
n = sample size.

The value for k3 dedicated to Normal Distributions shall be taken from the Table at end of Step 3.

Step 3.2: Lower limit of tolerance interval for results following a non-normal distribution

The unilateral statistical tolerance interval shall be calculated for a confidence level of 95% and a fraction of population equal to 99.9999%. 

The lower limit of tolerance is represented by a line of constant survival rate defined by the formula given in previous step 3.1, with factors k3 based and calculated on the properties of a Weibull Distribution. The value for k3 dedicated to Weibull Distributions shall be taken from the Table below at end of Step 3.

+--------------+--------------+--------------+
|               Table for k3                 |
|     p = 99.9999 % and (1-alpha) = 0.95     |
+--------------+--------------+--------------+
| Sample size  |    Normal    |   Weibull    |
|              | distribution | distribution |
|       n      |      k3      |     k3       |
+--------------+--------------+--------------+
|      20      |    6.901     |    16.021    |
|      22      |    6.765     |    15.722    |
|      24      |    6.651     |    15.472    |
|      26      |    6.553     |    15.258    |
|      28      |    6.468     |    15.072    |
|      30      |    6.393     |    14.909    |
|      35      |    6.241     |    14.578    |
|      40      |    6.123     |    14.321    |
|      45      |    6.028     |    14.116    |
|      50      |    5.949     |    13.947    |
|      60      |    5.827     |    13.683    |
|      70      |    5.735     |    13.485    |
|      80      |    5.662     |    13.329    |
|      90      |    5.603     |    13.203    |
|     100      |    5.554     |    13.098    |
|     150      |    5.393     |    12.754    |
|     200      |    5.300     |    12.557    |
|     250      |    5.238     |    12.426    |
|     300      |    5.193     |    12.330    |
|     400      |    5.131     |    12.199    |
|     500      |    5.089     |    12.111    |
|    1000      |    4.988     |    11.897    |
|   infinite   |    4.753     |    11.408    |
+--------------+--------------+--------------+

NOTE: If sample size is between two values, the closest lower sample size shall be selected.

(h) Measures if the acceptance criteria are not met 
If a result of the burst test, peeling and corrosion test or adhesion test does not comply with the criteria detailed in the Table in paragraph (g), the affected sub-group of over-moulded cylinders shall be segregated by the owner for further investigations and not be filled or made available for transport and use.

In agreement with the competent authority or the Xa-body which issued the design approval, additional tests shall be performed to determine the root cause of the failure.

If the root cause cannot be proved to be limited to the affected sub-group of the owner, the competent authority or the Xa-body shall take measures concerning the whole basic population and potentially other years of production.

If the root cause can be proved to be limited to a part of the affected subgroup, not affected parts may be authorized by the competent authority to return to service. It shall be proved that no individual over-moulded cylinder returning to service is affected.

(i) Filling centre requirements
The owner shall make available to the competent authority documentary evidence that the filling centres: 
- Comply with the provisions of packing instruction P 200 (7) of 4.1.4.1 and that the requirements of the standard on pre-fill inspections referenced in the Table of packing instruction P 200 (11) of 4.1.4.1 are fulfilled and correctly applied;
- Have the appropriate means to identify over-moulded cylinders through the electronic identification device;
- Have access to the database as defined in (d);
- Have the capacity to update the database;
- Apply a quality system, according to the standard ISO 9000 (series) or equivalent, certified by an accredited independent body recognized by the competent authority.