How much weight could one sealed-up stormwater pipe support on a water surface?

Question

I'm thinking about buying a few stormwater pipes, sealing them up, and building a float. How many would I need though? How much weight will one of these things carry?

The ones I've laid my eyes on are 6 metres long and have a diameter of 9 centimetres, are made from PVC, and weigh about 5 kilos.

Answer 1

If the outside diameter is 0.09m, and the pip is 6m long the volume is 6 x 0.045 x 0.045 x Pi =  0.038 cubic metres or 38 litres.

Submerged it will displace 38 litres ie 38 kg of water.

So, since it weighs 5kg it will support 33kg before submerging.

What's the plan?