14 Jan Why ASTM Coupon Racks?
A Corrosion Coupon Rack is an assembly of pipework that houses 1 or more metal coupons suspended in the water flow through the pipework of the coupon rack. The coupons are basically a piece of metal that are accurately weighed before being inserted into the rack. When they are removed after a period of time, they are weighed again and the reduction in weight has a correlation to corrosion rate. (They are also inspected for pitting). The actual metal composition of the coupon should represent what is actually in the main water system so that this corrosion rate is representative of the corrosion rate in the main system.
The objective is to create the same environment in the coupon rack that the same metal type in the main water system will experience. So this means the same temperature, same flow rate, laminar water flow etc. In the absence of an Australian standard for achieving this, many have chosen to adopt the American standard. ASTM International is a Standards Organisation (click here) and the ASTM originally stood for American Society for Testing and Materials, but today is just known as ASTM International. Download a copy of ASTM D2688 here to gain an insight into all the requirements for a coupon rack that complies with this standard.
Common features of these coupon racks are:
- Compliant to ASTM D2688 specification for Dimensions and Flow – Standard Test Method for Corrosivity of Water in the Absence of Heat Transfer (Weight Loss Method)
- Mounted on PVC backboard for easy installation
- Tue Union ball valves fitted on the inlet and outlet for easy isolation of flow when removing coupons, and for easy retrieval of coupons when they become detached from holder.
- Flow maintained at a fixed rate during a wide range of differential pressure across the inlet and outlet of the rack
- Quick release coupon holders.
Installation of the rack is recommended so that the outlet water from the rack runs to atmosphere, ideally to the tower basin.
To learn more about our Coupon Racks and parts, go to CWC Coupon Racks