All gas cylinders are subject to an initial test and inspection to ensure serviceability before use, followed by regular periodic inspections and tests to ensure its continued serviceability. The cylinder is stamped with the date these inspections and tests are carried out. The British Compressed Gas Association (BGCA) provides a systems of coloured date rings which gives a quick visual indicator for the next periodic inspection. The ring can be found on cylinder neck. The colurs and shapes repeat every 18 years.