Reviewers Note: Words/phrases in blue will be links to specific diagnostic procedures when this document is published in Freshdesk.

CNG Cylinder Inspection Manual

DSM.0084 Ver. 4.0 October 30, 2023
Introduction
About this Manual
This manual contains specific information pertaining to the inspection of Type 4 cylinders designed and
manufactured by Hexagon® Agility®.* It should not be applied to cylinders made by other manufacturers.
It is the responsibility of the vehicle OEM or third party installer to provide this manual to the appropriate
personnel and to ensure its accessibility. Appropriate personnel includes, but is not limited to, those who are
responsible for the inspection of cylinders.
A thorough understanding of the information provided in this manual is required for the safe and proper product
inspection. If further information is needed or questions arise, contact Hexagon Agility.
Hexagon Agility endeavors to maintain comprehensive and accurate product and service information. We reserve the right to make changes at any time to manuals
and other materials. Please contact Hexagon Agility FleetCare to ensure you have the latest version.

*Applies to cylinders labeled under Agility Fuel Solutions, Hexagon Lincoln, and Lincoln Composites

Inspection Types, Tools, and Supplies
Hexagon Agility cylinders must be inspected to ensure continued performance and safety. This section should
be read thoroughly prior to performing an inspection. Cylinder specifications, as noted in the design parameters
(DP), should also be reviewed.

Pre-Delivery Visual Inspection
Hexagon Agility requires the fuel system OEM to perform a thorough inspection of the cylinder prior to the vehicle
being put into service. The inspection should include the following checks:
Item Description
1

signs of leaks

2

signs of cylinder damage

3

4

Examples
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










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rotten egg smell
hissing sound
abrasions
chemical damage
cuts
debris around cylinder(s)
dents
dings
excessive heat damage
gouges
loose fibers
scrapes
etc.

signs of cylinder mount damage

mounts, rubber pads, or hardware
 loose
 damaged
 missing

cylinder clearance

minimum distance from vehicle and other fuel
system components (refer to cylinder DP and
fuel system OEM specifications)

5

cylinder labels






visible
in place
legible
cylinder is within the OEM “do not use after”
expiration date

Pre-Trip Visual Inspection
The driver should perform a cursory visual inspection before each trip. Look for the following items:
1. signs of cylinder damage – dents, dings, cuts, gouges, scrapes, etc.
2. signs of leakage – rotten egg smell or a hissing sound
WARNING
If damage is found, remove cylinder from service until a more in-depth inspection can be performed.

Inspection During Routine Maintenance
A trained technician should perform a general visual inspection during routine preventative maintenance such
as oil and fuel filter changes. Hexagon Agility recommends that shields, covers, and panels be removed, where
possible, to make the cylinder surface visible.
NOTICE
Use soap and water to clean cylinder and mount surfaces of road grime and grit before inspection.
Inspect for the following items:
Item Description
1

signs of leaks

2

signs of cylinder damage

Specifics














rotten egg smell
hissing sound
abrasions
chemical damage
cuts
debris surrounding cylinder(s)
dents
dings
excessive heat damage
gouges
loose fibers
scrapes
etc.

3

signs of cylinder mount damage

mounts, rubber pads, or hardware
 loose
 damaged
 missing

4

neck mount cylinders

signs of wear on bosses, mount blocks, and
bushings

5

strap mount cylinders

shifting of rubber pads, cracking of rubber
pads, or other damage to rubber

6

cylinder labels






visible
in place
legible
cylinder is within the OEM “do not use
after” expiration date

WARNING
If damage is found, remove cylinder from service until an in-depth inspection can be performed.

Inspection Tools and Supplies
Item Description

Purpose

1

shop light

illuminate fuel system components

2

inspection mirror

visual access to back surfaces of cylinders

3

hand tools

remove / replace fuel system covers, mounts,
plumbing

4

depth gauge / micrometer / caliper

measure cylinder surface and boss damage

5

neck bushing go-no-go gauge, p/n 24200183

measure cylinder neck mount to bushing gaps

6

fuel receptacle go-no go tool, p/n 10300140 or coin

perform tap test

7

Swagelok® Snoop® or other leak detection fluid

leak detection

8

clean water and mild detergent

clean grit and road grime from cylinders

9

cleaning cloths or wipes

clean grit and road grime from cylinders

10

notepad

record inspection findings

11

camera

document cylinder damage

When Inspections Must be Performed
WARNING Always perform a Periodic Full Visual Inspection of the cylinder(s) immediately if:
1. Cylinder or vehicle has been in an accident involving collision, fire, or any event that may have caused
external or internal damage, or
2. Cylinder seems to be behaving oddly. This includes but is not limited to, emission of CNG odor, unexpected
loss of gas pressure, snapping or hissing sounds, rattling, and any indications of loose parts, or
3. Cylinder is believed to have been pressurized above its maximum fill limit as indicated on the label.
4. Cylinder inspection is a required part of full CNG fuel system inspection which is required every 12
months or less per U.S. Department of Transportation and Canadian federal requirements.
The Hexagon Agility Statement of Service document specifies the recommended inspection frequency for each
cylinder according to its certifications.
Some areas have specific requirements for CNG cylinder inspections. Check with the local authority having
jurisdiction (AHJ) for the most recent requirements.

NOTICE
If there is a difference between inspection intervals specified in this manual and the requirement of the
authority having jurisdiction, the more stringent requirement applies.
For convenience, Hexagon Agility recommends other vehicle maintenance tasks, such as engine oil and fuel
filter changes and the yearly DOT inspection, be matched with the cylinder periodic full visual inspection.

Inspection Preparation
Cylinder History
The inspector should question the owner / fleet manager and vehicle operator(s) about any known incidents that
may have caused damage to the cylinder or any unusual observations. Additionally, the service history of the
cylinder, including any rework or repair that may have been performed since its last inspection, should be
supplied to and reviewed by the inspector.

Cylinder Access
Remove shields, covers, and panels, where possible, to make the cylinder surface visible.

Washing
The exterior surface of the cylinder should be washed prior to performing this inspection.
NOTICE
Hexagon Agility recommends washing the cylinder by hand with water or a mixture of water and a mild
detergent. If using a detergent, ensure the cylinder and surrounding components are thoroughly rinsed
with water.
NOTICE Never use a high-pressure washer or steam cleaner on cylinder surface/system components.
WARNING Never use a steam cleaner on or near pressure relief devices (PRDs) or trigger lines.

Inspection Criteria
Composite Inspection
Visually inspect the composite for signs of damage including abrasion, impact, weathering, excessive heat,
chemical attack, leakage, and unraveling.

Abrasion Damage
Abrasion damage may occur when an object contacts the surface of the composite. Light-load abrasion appears
smooth and polished (FIGURES 3 and 4), while high-load abrasion appears as gouges or cuts (FIGURES 5 and 6).
The severity of the abrasion should be evaluated by the depth of the damage as shown in TABLE 1. High-load
abrasion should also be evaluated for impact damage.
TABLE 1. Abrasion Damage Levels and Disposition

Abrasion Depth

Damage
Level

inches

millimeters

1

0.000 ≤ 0.010-in

0.00 ≤ 0.25 mm

field repair

2a

0.011 ≤ 0.035-in

0.26 ≤ 0.89 mm

field repair

2b

0.036 ≤ 0.050-in

0.90 ≤ 1.27 mm

contact CCTS

3

> 0.050-in

> 1.27 mm

Disposition

decommission and dispose of cylinder

FIGURE 3. Surface scratches categorized as Level 1 abrasion damage.

FIGURE 4. Matte surface texture from Level 2a abrasion damage.

FIGURE 5. Gouge in the composite categorized as Level 2b abrasion damage.

FIGURE 6. Level 3 abrasion damage where multiple layers of composite are visible.

Impact Damage
Severe structural damage can be caused from impacts. Impact damage may occur during shipping, installation,
or while in service (e.g., vehicular accident).
Since composite cylinders tend to return to their original shape after an impact and typically do not dent like
metal cylinders, a simple visual check is not enough. Damage may be hidden within the composite wall. This is
particularly true if the object impacting the cylinder is blunt and relatively smooth. Impact damage types are
delineated in TABLE 2.
TABLE 2. Impact Damage Types and Descriptions

Impact damage
category
surface damage

Description
damage to composite shell including cuts, gouges, scrapes, scuffs, chips, punctures,
and change in coloration or appearance. Surface cracks may appear circular or linear.

permanent
deformation

depression of composite surface resembling a dent

softness or
deflection

composite surface moves in response to pressure applied with hands

damage to cylinder
end bosses and /or
hardware
damage to dome
protection

signs of physical scrapes and scuffs to cylinder components including valves, plumbing,
fittings, pressure relief devices, and mount hardware

cracks in or loss to cylinder end dome caps