Carbon steel 900# Orifice RTJ flange coating/paint
Carbon steel 900# Orifice RTJ flange coating/paint
(OP)
A carbon steel 18"SCH40 900# orifice flange that we procured arrived coated with black paint. I am concerned that the coating will interfere with the RTJ groove on the flange. Is this a problem? Also, the inside of the flange will be exposed in the pipeline. Should I be concerned about flaking of the paint downstream in the pipeline?





RE: Carbon steel 900# Orifice RTJ flange coating/paint
It might be something similar to Impreglon (which would probably be red in colour), in which case I'd leave it alone. Other than that, your concerns are probably valid.
Regards,
SNORGY.
RE: Carbon steel 900# Orifice RTJ flange coating/paint
RE: Carbon steel 900# Orifice RTJ flange coating/paint
RE: Carbon steel 900# Orifice RTJ flange coating/paint
RE: Carbon steel 900# Orifice RTJ flange coating/paint
Just to be on the safe side, and assuming that you might not need the full flange rating, I checked the 18" Sch 40 material against a Class 600 pressure rating and it does not meet that either.
Assuming typical A106-B pipe with A105 flanges, 18" Sch 40 material has a rating of about 7700 kPa (1115 psi) even with zero corrosion allowance (per B31.3).
RE: Carbon steel 900# Orifice RTJ flange coating/paint
RE: Carbon steel 900# Orifice RTJ flange coating/paint
As for the Sch. number, oops! These numbers mean something, so be careful.
RE: Carbon steel 900# Orifice RTJ flange coating/paint
Class 900 flanges would typically have a rating of 15,320 kPa (2220 psi)
Depending on the actual required design pressure, and the required corrosion allowance, the Sch 80 material may or may not be acceptable.
If you could let us know the following, I could tell you what schedule would be required:
- Design Pressure
- Corrosion Allowance
- Material (e.g., A105)
- Design Code in use (e.g., B31.3)
However, if you want full flange rating with a typical zero corrosion allowance, with A105 material then you would need a min of Sch 100, if you wanted a typical 1/16" corrosion allowance then you would need a minimum of Sch 120 (all per B31.3).
RE: Carbon steel 900# Orifice RTJ flange coating/paint
-Corrosion allowance = None
-Material = A105/A106
-Design code = B31.3
So it appears that SCH80 is technically acceptable. However, the SCH80 per B31.3 does not match the rating of the CL900 flanges per B16.5. Very enlightening--thanks for all the input!
I noticed on B16.5 that the flange pressure rating for CL900 drops with increasing temperature. Is there a similar temperature de-rating that applies for B31.3 piping? My process temperature range is for 60-75C. This particular flange is for use in an anti-surge system for a pipeline compressor.
RE: Carbon steel 900# Orifice RTJ flange coating/paint
Now for the P/T ratings. The calc's are based on a formula that results in a decrease in pressure with an increase in T or a decrease in wall thk. (smaller Sch. no.) or a change in material (due differences in the ultimate and tesile strengths of the various materials themselves). But this is all covered under B31.1 or B31.3 and is well established.
RE: Carbon steel 900# Orifice RTJ flange coating/paint
The next step is calculate the required wall thickness and an 18" Sch 80 section of pipe (at less than 100 F) calculates as good to 1893 psig with zero corrosion allowance.
Consequently, you order an 18" Sch 80 bore Class 900 flange to match the pipe and everything meets code just fine.