Minimum thickness for furnace convection tubes

[kevlar49]

I am trying to determine the retirement thickness for tubes in a convection section. Hoop stress induced elastic/creep rupture does not limit. I am now going into bending stress calcs in API 530, but wanted to know if there are any other considerations besides those given in API 530? material is over designed (5Cr where CS used to be) issue was sulfidation.

 

[metengr]

kevlar49;
Is the tube current tube wall wastage localized or is it general tube wastage? If these are convection pass tubes in a furnace as you state, what is the estimated metal temperature and actual tube material specification? If you can supply this information, I can check in Section II, Part A for allowable stress values for this tube material. If you are indeed below the envelope for time dependent effects (creep deformation), you might be surprised at how much remaining useful service life there is excluding low cycle fatigue.

 

[davefitz]

It often happens that the min wall thickness may be defined by fabrication requirements- it is difficult to bend or weld on tubes thinner than xxxx thick, regardless of in service stresses.