[ cylinders ] magazine , achieving complete leak tightness can prove to be a challenge , too . structure of testing , certification , and product control in various ways .
It may appear implausible , but there is always some extent of leakage present due to the permeation of the liner material . Typically , the liner is made of a blow-moulded material that is integrated into the cylinder ’ s design , providing the necessary gas-tight properties of the product .
Elongation
The principle of elongation refers to the ‘ flex ’ of a cylinder , or the increase in internal volume when the cylinder is pressurised from atmospheric pressure to , for example , 700 bar . The most costefficient solution is a cylinder that is able to maintain strength and gas tightness with a minimal amount of fibre material . Of the few components that form a cylinder , the fibres are the most valuable part .
Load cycles
During the lifetime of a cylinder , it will be pressurised numerous times , causing stress on the material in a mechanical way and also being influenced by the dynamics of temperature increase and decrease . Fast filling , which is essential in vehicle applications such as cars , trucks , and buses , involves filling the cylinder with high flow and pressure while pre-cooling the gas to -40 ° C to prevent temperature increase inside the cylinder and ensure safe filling .
While the above summary touches on some of the key parameters and characteristics , there are of course many more details to elaborate on . But what happens when a cylinder manufacturer aims to introduce its product to the market ? How can they ensure that the market and its users can trust in a safe and well-engineered design ? The answer is testing .
Standards and homologation
Several standards are applicable throughout the market , each accepted or harmonized by a
The applicable standard and test program depend on the geographical area where the cylinder will be marketed .
National standards are required for cylinders in emerging markets like China and India , and existing standards are mainly adopted as they have been in place for quite some time . The automotive market for hydrogen cylinders is by far the most established in terms of standardisation and adoption .
The North American market has its own method of certification and does not necessarily involve an independent party for certification and product control . However , the standard used ( HGV 2 ) is well formed and extensive .
In the European market , the UN ECE R 134 is obligatory for vehicle-level certification , and a national authority is involved in certification and production control ( conformity of production ).
The structure for certification of cylinders in the transportation sector , with hydrogen as cargo , is organised differently . A notified body , accredited and qualified , is involved in the technical assessment of the design and production control .
In any case , extensive testing is required .
Testing
Returning to the requirements for a cylinder to be considered fit for use , let us have a brief look at the test methods used . Hydraulic testing is used to determine the strength of the cylinder . One of the first parameters required is the burst pressure of a cylinder to align the theoretical burst pressure ( by means of software modelling ) with the practical burst pressure .
Hydrogen Tech World | Issue 9 | April 2023 19