Dated: June 20, 2012 To, Chairman, Oil & Gas Regulatory Authority, 54-B, Old ZTE Plaza, Fazal-e-Haq Road, Blue Area, Islamabad

Subject: VISUAL AND ULTRASONIC EXAMINATION OF CNG VEHICLE CYLINDERS AS AN ALTERNATIVE TO HYDROSTATIC TESTING

Dear Sir,

CNG Safety Rules, 1992 refers to AS 2337.1 standard for hydrostatic testing of CNG

vehicle cylinder. Whereas according to the Clause 7.3.1 of AS 2337.1-2004 standard (copy

attached) hydrostatic testing of Type I CNG cylinder is not required if Ultrasonic examination is

carried out. The Clause clearly states that “Ultrasonic examination is an alternative to pressure

testing, applicable to the normal range of seamless metal gas cylinders, but is not suitable for

welded or composite cylinders.” In fact the name of the Section 7 of the AS 2337.1 is “Pressure

Test or Ultrasonic Examination”.

2. Conducting hydrostatic test and internal visual inspection can create safety problems

which are briefly discussed as under:

a) Hydrostatic testing is only suitable for Type II, Type III, Type IV and welded LPG/CNG

cylinders, as the integrity of welding and damage to the composite plastic fiber

wrapping is difficult to evaluate otherwise. The approved standard for CTL AS 2337.1

clearly exempt hydrostatic testing for Type I cylinders in which Ultrasonic examination is

carried out as an alternative (copy of relevant clause is attached for ready reference)

b) Hydrostatic testing can take the CNG cylinder to its plastic limit which can lead to failure

of CNG cylinder during service. The cylinder is also unnecessarily subjected to 1.5 times

its working pressure in hydrostatic testing during its service life.

c) A hydrostatic test requires disconnection of fuel lines, removal of the cylinder from its

mounting and removal of the cylinder 3-way valve. This process has to be reversed upon

installation of cylinder after the test, introducing many risks associated with it i.e.

improper installation of fuel lines, valve and cylinder, damaging of the cylinder valve or

cylinder neck/mounting, reduction in thread strength, thread damage, rubber pad

damage and leakage.

d) Implementing of a hydrostatic test can increase the chance of internal corrosion as

cylinder is filled with water during testing, any water retained after the test could cause

corrosion or affect engine performance.

e) The most common cause for cylinder rejection in a hydrostatic test is some kind of

problem with the hydrostatic test equipment itself. This includes false reading,

calibration of pressure gauge/relief valve, test interpretation etc. CTL in Pakistan are

mostly using locally fabricated equipment which is a copy of the OEM design and is not

reliable. A split second human error can take a cylinder into plastic stage where it is

permanently deformed due to increase in hydrostatic pressure.

f) If there are defects in the cylinder such as folds, microscopic cracks, gouges or similar

damage, the hydrostatic test results are likely to be the same as for good cylinder.

Worthington CNG Storage Cylinders are a good example of such case; these were tested

at HDIP CTLs prior to installation at CNG station on the directives of OGRA yet failed

during the service even though the cylinders pass the Hydrostatic test requirements.

g) Hydrostatic testing requires emptying of CNG cylinder which results in release tens of

thousands of kg natural gas into the atmosphere. Natural gas is a GHG that is 21 times

more potent than CO2.

h) NZS 5454 and similar vehicle manufacturing standards i.e. ISO 11439, NGV2, have an

extensive array of material, qualification and batch tests to ensure that the materials are

acceptable, the designs are sound and the manufacturing process is repeatable. These

standards have more test requirements than for conventional gas cylinders. The drop

test, gunfire test, pressure cycling test, proof test, burst test and environmental test

provide considerable assurance that the cylinders can sustain damage or environmental

exposure and still remain safe during service life. Hence, there is no need to carry out

periodic hydrostatic testing of Type I CNG cylinder.

i) There was not a single NGV cylinder that has been reportedly rejected because of the

internal corrosion as there are traces of compressor oil in CNG which prevent the

cylinder from internal corrosion. ISO 9078:2006 (E) states that there have been no

reports of steel cylinder failures due to corrosion in NGV Service.

j) Taking into account all the aforementioned factors, it is obvious that requiring a

hydrostatic test only introduces much risk and cost with little, if any, gain. Many

Regulatory Authorities are looking for alternatives to hydrostatic testing because they

realize that it is not adding much value. There is general consensus in the leading NGV

OEM that the risk associated with hydrostatic testing are much higher than its benefits.

3. A pressure vessel inspector can declare the CNG cylinder fit for further use with the help

of visual and ultrasonic inspection tools without Hydrostatic testing. In this regard, standards

like Compressed Gas Association (CGA) C-6.4 (Methods for External Visual Inspection of Natural

Gas Vehicle and Hydrogen Vehicle Fuel Containers and Their Installations) and ISO 9078: Gas

cylinders — Inspection of the cylinder installation, and requalification of high pressure cylinders

for the on-board storage of natural gas as a fuel for automotive vehicles can be included in the

approved list of standards for periodic testing of CNG Cylinders.

4. Ultrasonic testing even identifies small faults, such as cracks, corrosion, pits and gouges

that are not always found during the internal visual inspection required as part of a standard

hydrostatic test. The requirements of internal visual examination are waived off for ultrasonic

testing of cylinders as it produces highly accurate measurements. This give additional benefit

that the cylinders are not required to be de-valved. Furthermore, the residual contents do not

have to be drained in Ultrasonic examination and it provides more detailed analysis than the

standard hydrostatic test.

5. In the view of above, it is requested that Oil & Gas Regulatory Authority (OGRA) may

allow that NGV Type I seamless steel cylinders shall be re-qualified by visual and ultrasonic

inspections after every 5 years or less as an alternative to Hydrostatic testing.

Regards,

Mr. Asim Riaz

NGV Owner/Driver,

B.E Mechanical, B.Sc Math Physics, Master Energy Management,

The writer has about a decade long experience in evaluation, inspections, technical reporting of

CNG cylinders accidents and is well versed with CNG cylinder manufacturing/testing standards.

Cc:

Honourable Federal Secretary, M/o Petroleum & Natural Resources

C.I.E, Department of Explosives, M/o Industries

Registrar, OGRA