Internal and/or external protective coatings for steel tubes. Specification for hot dip galvanized coatings applied in automatic plants.
The quality designation shall consist of one of the following to identify the intended application of the tube:
• A – for gas and water installations, including water intended for human consumption;
• B – for other applications;
followed by a full stop and a number to identify the special requirements for that application (eg. A.1, B.1).
A number of options are permitted by this European Standard:
1) The minimum local coating thickness on the outside surface is specified. This option applies to coating qualities A.1, A.2 and A.3 only.
2) The chemical composition of the coating is specified (the chemical composition of the coating shall not exceed the following: Antimony 0,01%, Arsenic 0,02%, Lead 0,8%, Cadmium 0,01%, Bismuth 0,01%). This option applies to coating qualities A.2 and A.3 only.
3) The minimum local coating thickness required is in excess of 55 µm. This option applies to coating quality B.1 only.
4) The type of post galvanizing treatment is specified.
5) A post galvanizing treatment is precluded.
- Minimum local coating thickness on the inside surface except at the weld bead:
A.1: 55 µm
A.2: 55 µm
A.3: 45 µm
- Minimum local coating thickness on the inside surface at the weld bead:
A.1: 28 µm
- Minimum local coating thickness on the outside surface:
B.1: 55 µm
B.2: 40 µm
B.3: 25 µm
The coating on both the inside and outside surfaces shall be continuous, smooth and free from flux residues on the significant surface. NOTE: White marks on the surface of the coating (commonly known as “wet storage stain”) are permitted if the requirements for coating thickness are met.
Service life increases with increase in coating thickness, but thicker coatings are more susceptible to mechanical damage.
When tested (the flattering test, the bend test) the coating shall show no evidence of flaking on the significant surface. In addition the coating shall show no evidence of cracking on the significant surface when subjected to the bend test. Flaking adjacent to cut faces shall not be cause for rejection.