ISO 12944-3:2017标准是防腐涂料在钢结构上应用的设计考虑方面的标准。该标准主要包括以下内容：

1. 环境条件的考虑
在设计防腐涂料系统时，需要考虑钢结构所处的环境条件，包括气候、大气污染、土壤条件等。这些因素会影响涂料系统的选择和设计。

2. 涂料系统的选择
根据钢结构所处的环境条件，需要选择适合的涂料系统。涂料系统的选择应该考虑到涂料的耐腐蚀性、耐磨性、耐紫外线辐射性等因素。

3. 涂料系统的设计
涂料系统的设计应该考虑到涂料的厚度、涂层的数量、底漆和面漆的选择等因素。涂料系统的设计应该符合相关的国家标准和规范。

4. 施工
涂料系统的施工应该符合相关的国家标准和规范。施工前需要对钢结构进行表面处理，包括除锈、清洗等。施工时需要注意涂料的厚度、涂层的数量、涂料的干燥时间等因素。

总之，ISO 12944-3:2017标准为防腐涂料在钢结构上的应用提供了设计考虑方面的指导。该标准的实施可以提高钢结构的耐腐蚀性和使用寿命，保护钢结构的安全性和可靠性。

相关标准
- ISO 12944-1:2017 Paints and varnishes — Corrosion protection of steel structures by protective paint systems — Part 1: General introduction
- ISO 12944-2:2017 Paints and varnishes — Corrosion protection of steel structures by protective paint systems — Part 2: Classification of environments
- ISO 8501-1:2007 Preparation of steel substrates before application of paints and related products — Visual assessment of surface cleanliness — Part 1: Rust grades and preparation grades of uncoated steel substrates and of steel substrates after overall removal of previous coatings
- ISO 8502-3:2017 Preparation of steel substrates before application of paints and related products — Tests for the assessment of surface cleanliness — Part 3: Assessment of dust on steel surfaces prepared for painting (pressure-sensitive tape method)
- ISO 8503-1:2012 Preparation of steel substrates before application of paints and related products — Surface roughness characteristics of blast-cleaned steel substrates — Part 1: Specifications and definitions for ISO surface profile comparators for the assessment of abrasive blast-cleaned surfaces