BS EN ISO 28763:2019 pdf – Vitreous and porcelain enamels — Regenerative, enamelled and packed panels for air-gas and gas-gas heat exchangers — Specifications.
1 Scope This document specifies the minimum requirements and the functional characteristics of enamel coatings applied by any process, such as wet dipping, wet flow-coating, wet spraying, wet electrostatic spraying, wet electrodeposition or dry-powder electrostatic spraying, to profiled steel heat exchanger panels in regenerative heat exchangers, before and after packing in baskets. For very severe service conditions, or to obtain extended operational life, more stringent limits can be agreed between customer and supplier. 2 Normative references The following documents are referred to in the text in such a way that some or all of their content constitutes requirements of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies. ISO 105-J03, Textiles — Tests for colour fastness — Part J03: Calculation of colour differences ISO 2178, Non-magnetic coatings on magnetic substrates — Measurement of coating thickness — Magnetic method ISO 4534, Vitreous and porcelain enamels — Determination of fluidity behaviour — Fusion flow test ISO 7991, Glass — Determination of coefficient of mean linear thermal expansion ISO 8289:2000, Vitreous and porcelain enamels — Low voltage test for detecting and locating defects ISO 19496-1, Vitreous and porcelain enamels — Terminology — Part 1: Terms and definitions ISO 28706-2:2017, Vitreous and porcelain enamels — Determination of resistance to chemical corrosion — Part 2: Determination of resistance to chemical corrosion by boiling acids, boiling neutral liquids, alkaline liquids and/or their vapours ISO 28723, Vitreous and porcelain enamels — Determination of the edge covering on enamelled steel plate to be used in heat exchangers ISO 28764, Vitreous and porcelain enamels — Production of specimens for testing enamels on sheet steel, sheet aluminium and cast iron
4.5 Pickling speed If required by the enameller, the pickling speed shall be determined in accordance with EN 10209:2013, Annex B, and an acceptable level shall be agreed with the steel manufacturer. 5 Enamel frit 5.1 Delivery Enamel frit shall be ordered by the enameller with a certificate conforming to the requirements of EN 10204:2004, 3.1, including the results for the items given under 5.5 and 5.7. The tests in 5.4 and 5.6 shall be carried out whenever there is a change in the frit or a change in the milling formula. When taking delivery of “ready to use” enamel, enamel slip or enamel powder, the enameller may ask for additional requirements for the application properties in the material certificate. Any other requirements and the test recipes shall be determined by consultation between the enameller (and/or customer) and the frit manufacturer. 5.2 Coefficient of expansion If required by the enameller, the coefficient of expansion shall be determined in accordance with the house test of the manufacturer of the enamel frit (base material for “ready to use” enamel, enamel slip or powder enamel) or in accordance with ISO 7991. 5.3 Fusion flow If required by the enameller, the fusion flow shall be determined in accordance with the house test of the manufacturer of the enamel frit (base material for “ready to use” enamel, enamel slip or powder enamel) or in accordance with ISO 4534. 5.4 Boiling-water (vapour phase) resistance If required by the enameller, the boiling-water (vapour phase) resistance shall be determined in accordance with ISO 28706-2:2017, Clause 14. When determined in this way, the maximum loss in mass of the enamel coating shall be as given in Table 1.
6.3 Thermal-shock resistance Test specimens for the determination of thermal-shock resistance shall be prepared in accordance with ISO 28764 and shall be pre-treated and enamelled under the same conditions as for the production of the heat exchanger. They shall have an enamel layer thickness of 150 µm ± 20 µm. The thermal-shock resistance shall be determined in accordance with Annex A at a test temperature of 350 °C on at least three test specimens. After testing five times at the test temperature, the test specimens shall show no damage. The test shall be carried out on every 5 000 kg of enamel frit. 6.4 Fundamental defects A 100 % visual examination of the enamelled surface shall be carried out for fundamental defects. The enamelled surface shall be free of fundamental defects such as blisters, burn-off, chipping, copperheads, cracking, crazing, fish scaling, spalling and tearing. The enamelled surface shall be visually examined from a minimum distance of 1,5 m and a maximum distance of 2,5 m either in natural light or in D65 artificial daylight in accordance with ISO 105-J03. NOTE Fire tool marks can be accepted. 6.5 Open defects Open defects down to the basis metal shall be detected in accordance with ISO 8289:2000, method B. In a random check of 10 pairs of panels out of a production of 10 000 pairs of panels, the average number of open defects shall be as given in Table 2. This rate of sampling is sufficiently representative of the production whenever the results are within the specified limit. If the results are outside the specified limit, sampling shall be extended to between 2 and 5 per 1 000.