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

Tanks are usually made of the following materials:

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

Some materials are more appropriate than others.

Don't forget that they are used to store waste (liquid that generates sulfurous gases and odors when decomposed). If the tank manufacturer certifies that they comply with the ISO:8099 standard, you can rest assured, but there are a wide variety of tanks on the market that carry the ISO identification, but are not approved.

Based on our experience, we can affirm that flexible tanks , which adopt the contour of an irregular space when filled, are not recommended, except as a temporary means of waste containment. Flexible tanks will not be completely emptied, as the tank wall will bend around the discharge hole when the tank is almost empty. Even though the tank has ventilation, residual bags will cause bad odors to permeate in 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 rupture.

Stainless steel tanks are generally resistant to the effects of residue, although they cause problems in 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 applied after manufacturing or a very low carbon steel (316) is used. L or equivalent) correctly welded.

Fiberglass tanks are also resistant to the effects of residue. The manufacturer must guarantee that the necessary tightness and pressure tests have been carried out.

Polyethylene tanks, manufactured by rotational molding, or by welding, have given very good results over many years. It also does 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. Tanks with thinner walls (less than 9.5 mm) used for the containment of drinking water will not be able to meet the legal requirements for resistance to positive pressure. ISO standards require that the tank not leak after exposure to a pressure of 20Kpa for 5 minutes.

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

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