Clasification Society Rules and Regulations - Rules and Regulations for the Classification of Offshore Units, January 2016 - Part 8 CORROSION CONTROL - Chapter 1 General Requirements for Corrosion Control - Section 2 Riser systems
Section 2 Riser systems
2.1 General
2.1.1 Riser systems are to be suitably protected against corrosion. It is recommended that this be achieved using a coating combined with a cathodic protection system. Account should be taken of possible temperature effects. Other equivalent methods of protection will be considered.
2.1.2 The splash and boot topping zones of risers are to be specially considered. A corrosion allowance will be required in addition to any coatings. The corrosion allowance should be defined based on corrosion rate and service life in the relevant location and a default 6mm applied unless demonstrated to be onerous based on environmental conditions, materials and service life, deviations shall be agreed with LR. Risers in J-tubes, etc. will require separate assessment of protection.
2.2 External coatings
2.2.1 Paint or protective coatings are generally to be chosen in conjunction with the system of cathodic protection.
2.2.2 The performance of the coating materials used should be proven by previous service or by extensive and documented laboratory testing.
2.3 Internal protection
2.3.1 The method of internal protection is to take into account the corrosivity, bacterial content, solids/abrasive content, flow characteristics and temperature and pressure.
2.3.2 Materials or systems (e.g. liners) are to be evaluated against the service nature of the product to be conveyed. Proprietary specifications and in-service history are to be submitted as required by LR.
2.3.3 Where internal protection is proposed by use of corrosion inhibitors, the properties, compatibility and effect on product conveyed are all to be documented and submitted.
2.4 Cathodic protection systems
2.4.1 Cathodic protection systems are to comply with the requirements of Pt 8, Ch 2 Cathodic Protection Systems.
2.4.2 Visual inspection surveys with measurements of potential are to be taken periodically and any deficiencies in terms of potential readings above the protection potential of -0,8V Ag/AgCl or detached anodes corrected by the addition of extra sacrificial anodes or adjustment of ICCP system controls.
2.4.3 For ICCP systems, measurements are to be taken to confirm that there is no over-protection. Over-protection is considered to be readings more negative than -1.2V Ag/AgCl.
2.4.4 Stray currents, current drain and including that from the mooring system and interference from ships, other vessels or installations in the vicinity are to be evaluated and appropriate measures taken.
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