Replacement Criteria of EDC Furnace Tubes

[rtsd]

We have EDC (Ethylene Die Chloride) furnace in VCM (Vinyl Chloride Monomer) plant, Design Temp. is 490C and Design Pressure is 4137 KPa, material of tube is Incoloy 800H, we have frequent failures in radiant section, by metallography we found internal oxidation of the tube, we have a NDT meter we are using for Ethylene Cracking Furnaces for %age carburization, the same we used with EDC tube it showed varying %age but these results are convincing to us because at 491C less chances of carburization. We are of the opinion that as this NDT tool is based on meagnetic permeability and both carburized and oxidized layers are magnetic so this NDT meter is not able to differentiate between carburization and oxidation.
We want to establish a criteria for tube retiring considering internal oxidation and other factors, we are also looking for NDT technique for oxidation check.

Expert opinion is required to check the oxidation and to establish retiring criteria

 

[Guest102023]

You really need to do a root cause failure analysis. I think you may be assuming more information than NDE is capable of providing.

 

[texasmike45]

Our EDC cracking furnaces are 20+ years old, horizontal radiant coils, 8" sch/40 Alloy 800H tubes, 15 radiant tubes per coil. 200 psig design pressure, maximum decoke temperature of 1250F. The furnaces are steam/air decoked annually and we inspect them annually. We perform EMAT and GUL testing on the bottom 5 tubes of each coil along with liquid penetrant and UT shearwave testing of the girth welds, LPT also of the skin thermocouple heat sheid attachment welds. We occasionally replace tube sections in the bottom 3 rows of each coil as a result of internal localized corrosion of the tube wall on the burner side of the tube. We have been very successful in detecting this corrosion using GUL and EMAT. We inspect all 15 radiant tubes on each coil every 5 years but have never detected any significant internal corrosion above the bottom 3 rows. We use a conservative tube retirement thickness of .170" which has served us well as we have not had an on-line tube failure in over 12 years.