LPG CYLINDER QUALITY STANDARDS
KS ISO 4706 is a Kenyan standard for LPG Cylinders manufacturing. The standard covers all requirements ranging from choice of material, minimum material thickness, manufacturing, testing and documentation. It is a requirement that the cylinder manufacturer provides the following to the client before manufacturing can start:
- Design Calculations showing minimum thickness, volume and expected burst pressure
- Engineering Drawings approved by client
BASIC CYLINDER PARTS
LPG Cylinder consists of four main parts.
Foot Ring (Base Ring)
This the part of the cylinder that sits on the ground. Its main function is to provide support and keep cylinder in upright position. It's ventilated to ensure no water accumulation to cause rust.
Its main function is to protect valve but on a 6Kg cylinder it also provides base and support to Grill.
This is the part of the cylinder that holds LPG. It is the pressure holding part and thus subjected to delicate design, manufacture and test process. It can be made of two or three parts welded together. The parts are welded in a controlled process that has to be either automatic or semi-automatic.
This is the part that shuts off gas or opens when required to control flow of gas. It is made from brass and mostly have self-closing mechanism.
Every LPG cylinder has permanent markings engraved on either Footring, Collar or sometimes on the body. This markings are indelible and reproduced whenever the portion holding them is replaced. Mandatory markings include:
- Manufacturer of Cylinder
- Manufacturing Standard
- Design Pressure
- Test Pressure
- Water Capacity (volume of the cylinder)
- Serial Number (each cylinder has a serial number)
- Tare weight
- LPG carrying capacity (in Kg)
- test date (consisting of month and year of last test date)
Test date of the cylinder is crucial to consumers as the law does not allow a cylinder to be in the market for more than eight years before being re-tested.
In addition to above markings, LPG cylinders also have other markings in bold ink showing tare weight and sometimes both tare weight of cylinder and expected total weight after refill.
CYLINDER MANUFACTURING TESTS
During manufacturing process, various tests are carried out on the cylinders. Some are 100% non-destructive testing while others are statistical destructive testing.
- Hydrostatic Test
All cylinders are subjected to water pressure of 30 bar (435 PSI). This test is mainly carried out to test body integrity of the cylinder. Some failures observed here are bulging, body leakage and deformation
- Pneumatic Leak Test
100% testing to detect any leakage from the cylinder. Compressed air at 7 bar (100 PSI) is injected into the cylinder and any leakages noted.
- Radiography Test
Statistical test carried out on welded joints. Porosity, cracks and lack of proper fusion are some of the faults checked.
- Bend and Tensile Tests
Carried out on welded joints of a sample cylinder. Main purpose is to test integrity of the welded joints.
- Burst Test:
Carried out on sample cylinders. Specimen is pressurized with liquid medium (mainly water) till it bursts. Burst pressure and volumetric expansions are compared with calculated values.
Every manufacturer of LPG Cylinders must provide the following documents to the client:
Complete set of drawings indicating the design and manufacturing processes the cylinders have gone through. The drawings also specify test parameters the cylinders have undergone during manufacture.
LPG cylinders are designed and major parameters calculated. Wall thickness (both at cylindrical and curved portions) are arrived at after putting in consideration yield strength of material, test pressure and of the cylinder.
Determine the volume of cylinder required to hold the designed quantity carrying capacity. Inspection by approved person/body Inspection certificate is issued by approved body that witnesses and confirms manufacturing process conforms to the standard.