BS ISO 8179-1:2017 pdf download – Ductile iron pipes, fittings, accessories and their joints — External zinc-based coating Part 1: Metallic zinc with finishing layer
5 Zinc-based coating
5.1 Pipeline component surface condition The pipeline component surface shall be dry and free from rust and any non-adhering particles or foreign matter such as oil or grease. The metallic zinc-based coating shall be applied to the as-cast annealed external surface of the pipeline component, or to a blast-cleaned or ground surface at the manufacturer’s discretion.
5.2 Method of application The metallic zinc-based coating shall be applied by a spraying process in which metallic zinc or zinc alloy is heated to a molten state and projected in small droplets by spray guns on to the pipeline component surface. The design and construction of the spray equipment are not within the scope of this document.
5.3 Coating characteristics The metallic zinc-based coating shall cover the outside surface of the pipeline component and shall be free from such defects as bare patches or lack of adhesion. A spiralled appearance is permissible provided that the zinc-based coating masses comply with the requirements of5.4. The manufacturer shall define those coating irregularities which are considered not detrimental to the performance of the coating system. Damaged areas of zinc-based coating caused by handling are acceptable, provided that the area of damage is less than 5 cm 2 per square metre and that the minor dimension of the damaged area does not exceed 5 mm. Greater areas of damage shall be repaired in accordance with 5.5.
5.4 Zinc-based coating mass The mean mass of zinc-based coating measured in accordance with7.1 shall be as follows:
— not less than 200 g/m 2 with a local minimum of 180 g/m 2 ;
— in low corrosive areas, by agreement between the purchaser and the supplier, 130 g/m 2 of zinc with a local minimum of 110 g/m 2 ;
— in case of very corrosive soils, the manufacturer and the purchaser may decide to use additional coating mass. The manufacturer shall visually inspect each pipeline component for quality and uniformity of coating and shall carry out regular measurements of zinc-based coating masses in accordance with the method described in 7.1. The factory quality control tests ensure conformity to the standard. Factory quality control tests shall be the sole determinant of coating thickness acceptance. Where informative field verification is required, one of the methods described in Annex A shall be agreed upon between the manufacturer and the purchaser.
For the selection of coatings in relation to the characteristics of soils, Annex B can be consulted.
5.5 Repairs to the zinc-based coating Areas left uncoated, e.g. under the test token, and coating damage in excess of that permitted in 5.3 shall be repaired by either a) metallic zinc spray complying with 5.4, or b) application of a zinc-rich paint containing more than 85 % zinc, by mass, in the dried film. The mean mass of the applied paint shall not be less than 20 % above the nominal coating mass of the metallic zinc-based coating.
6 Finishing layer After the zinc-based coating has been applied, the pipeline component shall be given a finishing layer of bituminous paint or synthetic resin compatible with the zinc-based coating. Application of this finishing layer may be done by any proven process such as spraying or brush coating at the manufacturer’s discretion. It shall uniformly cover the zinc-based coating and be free from bare patches or lack of adhesion. The mean dry film thickness of the finishing layer measured in accordance with 7.2 shall be not less than 70 μm with a local minimum thickness of 50 μm. The method of coating thickness measurement is at the manufacturer’s discretion. In order to avoid blistering, the mean dry film thickness of the finishing layer shall not exceed 250 μm.BS ISO 8179-1 pdf download.