These are black steel tubes or with subsequent galvanising by immersion in a molten zinc bath. They are also called “gas thread tubes”, which can be threaded for general domestic or industrial fl uid installations (low-pressure water, sprinkler systems), although they are also applicable for other uses, such as greenhouses, etc.

This type of tube has high mechanical strength and for this reason perform better under tensile stress, pressure, compression, etc., and greater resistance to external impact and attacks. Their main advantages are as follows:

• Mechanical resistance.
• Corrosion resistance.
• Fire resistance.
• Health.
• Long life.
• Overall safety.
• Versatility.
• Quality.
• Quality/price ratio.
• Standardisation.
• Certification.

They also have a low expansion coefficient at high melting temperature, and it is for this reason that they are highly resistant to fire and high temperatures. Consequently, they have fewer problems with regard to stress and deformation in the presence of high temperatures than tubes with other characteristics.

In terms of health, tubes made with galvanised material are considered by the World Health Organisation to be the most suitable type of tube for drinking water.