Since there are many articles explaining what Top Tension Risers (TTR) are, I will be discussing the Material Selection aspects when working/selecting the fit-for-purpose TTR.
All primary forgings, pipe, and structural materials should meet the requirements of API STD 2RD, Section 7, Materials.
Exposure to a cathodic protection system should be considered in the selection of all materials.
Forgings should meet the requirements of API STD 2RD. Forgings and Extrusions should meet ASTM A182 F22 grade material.
Structural equipment materials should meet the requirements of API STD 2RD.
All seals must be suitable for the fluid service intended. Typical practice is to design or specify corrosion resistant metal seals for use in flanged joint connections. An elastomer seal should be used to keep sea water away from primary flange seals.
Bolting for drilling riser flange connections should meet the standards of API STD 2RD, Section 7.10.3, with the exception that maximum bolt hardness should be limited to 32 HRC.
Pad-eyes and Lifting Gear
All material for pad-eyes, spreader bars, and lifting eyes should be 100% ultrasonically tested for laminations in accordance with ASTM A578 (acceptance standard Level II). Pad-eye holes should be bored or reamed and should have a uniform milled finish. All lifting pad-eyes, spreader bars, tri-plates and other lifting tools should be certified by a recognized classification society. All pad-eyes spreader bars and lifting eyes should be load tested to 1.5 times the safe working load with non-destructive testing performed prior to and after load testing.
Welding, Fabrication and Nondestructive Testing
Welding, fabrication and nondestructive testing (NDT) should meet the requirements of API STD 2RD.
All weld procedures should be qualified in accordance with applicable standards and reviewed/approved prior to use.