This International Standard deals with performance requirements for protective paint systems for offshore and related structures (i.e. those exposed to the marine atmosphere, as well as those immersed in sea or brackish water). Such structures are exposed to environments of corrosivity category C5-M and immersion category Im2 as defined in ISO 12944-2, with special stresses as given in Subclause 4.3 and Annex B of ISO 12944-2:1998. ISO 20340 can also be used for other structures, provided that the paints or protective paint systems selected comply with this International Standard. This International Standard places emphasis on high-durability paint systems, with the aim of minimizing maintenance and hence reducing safety considerations and environmental impact. It specifies additional test requirements over and above those specified for corrosivity category C5-M in ISO 12944-6. Hence, a system fulfilling the requirements for C5-M high durability in ISO 12944-6 will not necessarily fulfil the requirements of this International Standard and might thus need further testing to do so. The temperature range applicable for these paint systems is normally between -20 °C and +80 °C, and the performance testing is aimed at verifying suitability of the paint systems for this temperature range. The use of paint systems outside this temperature range shall be subject to agreement by the end user. Such agreement may include testing at the applicable temperatures. The paint systems for submerged service (Im2) are aimed at ambient operating temperatures up to a maximum of 50 °C. For higher operating temperatures, specific evaluation and performance documentation is needed. The selection of performance requirements should be considered in conjunction with the cathodic-protection design parameters.