Sanitation

Why is it important to identify what your blackwater tank is made of?

What material is my boat's holding tank made of?

Tanks are typically made of the following materials:

Flexible Plastic
Aluminum
Stainless steel
Fiberglass
Polyethylene (of various thicknesses)

Some materials are more appropriate than others.

Remember that they are used to store waste (a liquid that generates sulphurous gases and odours when it decomposes). If the tank manufacturer certifies that they comply with the ISO:8099 standard, you can rest easy, but there are a wide variety of tanks on the market that carry the ISO identification, but they are not approved.

Based on our experience, we can say that flexible tanks , which take the shape of an irregular space when filled, are not recommended except as a temporary means of containing waste. Flexible tanks will not be completely emptied, as the tank wall will bend around the discharge opening when the tank is nearly empty. Even if the tank is vented, residual pockets will cause odor permeation within a relatively short period of time.

Aluminum tanks They are generally treated with a resistant coating. Unfortunately, these coatings are not perfect and therefore corrosion or any defect, even the size of a needle point, will cause the tank wall to break.

Stainless steel tanks are generally resistant to the effects of the residue, although they do present problems at welded joints. The intense heat required to melt and join the steel edges causes the joints to lose their corrosion resistance unless a very high temperature process is used after fabrication or a properly welded very low carbon steel (316 L or equivalent) is used.

Fiberglass tanks are also resistant to the effects of waste. The manufacturer must ensure that the necessary leak and pressure tests have been carried out.

Polyethylene tanks, manufactured by rotational moulding or welding, have given very good results over many years. In addition, they do not present the corrosion problems associated with metal tanks. Polyethylene is a highly inert material and stable at constant temperatures of 48ºC. Its robustness and impact resistance are also very high.

Wall thickness is also an important factor. Thinner walled tanks (less than 9.5 mm) used for potable water containment will not be able to meet the legal requirements for resistance to positive pressure. ISO standards require that the tank should not leak after exposure to a pressure of 20 Kpa for 5 minutes.

The information in this article comes from studies carried out by the Sealand company, leader in the design and manufacture of sanitation systems .

If you have a tank installed on board, identify it and take the necessary precautions so that it does not cause you problems. If you have to install one, we hope we have provided you with the appropriate information.

Leave a Comment

Please note, comments need to be approved before they are published.