The standard PAM pipe coating consists of a layer of sprayed metallic zinc (200 g/m2 minimum), covered with bituminous paint (poresealer). It is an active coating, suitable for the majority of soils.
The zinc coating comprises:
- A layer of metallic zinc applied by electric arc spray gun (minimum quantity: 200 g/m2, which represents a 50 % increase over the French, European and International Standards, which prescribe 130 g/m2),
- A bituminous paint finish (pore-sealer), (minimum thickness 100 microns) or equivalent.
Zinc coating is an active protection, due to the galvanic action of the zinc/iron couple. It performs by a dual mechanism:
Formation of a stable protective layer
On contact with the surrounding soil, the metallic zinc slowly changes to a dense, adhesive, impermeable, and continuous layer of insoluble zinc salts. This
provides a protective screen. The pore-sealer, while facilitating galvanic protection and healing, also promotes a stable and insoluble layer of zinc conversion products.
This mechanism occurs first.
One of the particular features of external zinc coating is its capacity for restoring the continuity of the protective layer at points where it is locally damaged. The Zn++ ions migrate through the pore-sealer to plug the damage and are then converted into stable insoluble zinc products.
Advantages of 200 g/m2 zinc coating
PAM has chosen to increase the quantity of zinc to 200 g/m2 (instead of the 130 g/m2 recommended in standards).
This significantly increases the period during which zinc provides active protection for the pipe.
A 50% increase in the thickness of the zinc coating significantly increases the duration of the galvanic protection.
Standard EN 545 recommends using zinc-based coatings for most soil types. Backed by its extensive experience, PAM has selected zinc as the basic standard coating for all pipes it manufactures. There are, however, certain cases where the zinc coating needs to be enhanced with a polyethylene sleeve.
In extreme cases of very aggressive soils, the pipe will need to be completely isolated where it passes through highly corrosive areas.
PAM’s technical staff can carry out soil surveys at the customer’s request in order to recommend the most suitable protection. Also, because of its strength, the zinc coating is particularly well suited for transport, handling, storage and protection against falling backfill, thus providing lasting protection for pipes.
GB/T 13295: Ductile iron pipes, fittings and accessories and their assembly for water pipes. Recommendations and test methods.
GB/T 17456.1: Ductile iron pipes: external zinc coating.
Part 1: Metallic zinc and finishing coat.
Pore-sealer varnish has received a Sanitary Conformity Certificate (ACS) and complies with the provisions of the Decree dated 29 May 1997.