RTJ Flange Failure at Low Loads 2

[stoerw]

System Parameters: Design Press:651 PSI Design Temp: 656F
Piping Material: On Flange 1: A106 Gr.C 24" OD w/ 1.806 wall thickness
On Flange 2: A106 Gr.C 24" OD w/ 0.556 wall thickness

Background Information: We have to of these RTJ Flanges on different lines with the same setup. Pipe hanger inspection history has all hangers functioning properly on both lines. The East side line has been operating without issues. The west side line 50 feet or so from the other has a history of leaking at low loads on our power plant but stops leaking at higher loads. A couple years ago a new ring was installed, and a clamp was seal welded around the flanges to help prevent future leaks. The flange is now leaking again at low loads.

I'm reaching out to ask of possible failure modes for these conditions and possible recommendations for correcting them. I've read some standard failure modes on other threads, but to me most of them would lead to a constant steam leak and not just situational leaking. Due to the seal welded clamp the costs are high without much return to disassemble and inspect. The current option we are looking into is cutting out the flange completely and installing a tapered wall thickness, solid pipe in its place. So, please if you have the experience please reach out with the cause of the situational failure of our RTJ Flange.

 

[Andrew ONeill]

My experience (although with smaller diameters) is leaks in RTJ's are normally related to thermal expansion issues and/or external loads on the flanges.

However, if you have the chance, I'd cut out the RTJ flange and put in some RF flanges with a spiral wound gasket, or even better as you suggest, if the flange is not needed for maintenance, remove it completely and put in a welded pipe section.

*I'm making the assumption that someone will do the required pipe stress analysis / flexibility analysis if such changes were to occur.



Andrew O'Neill
Specialist Mechanical Engineer
Australia

 

[Krausen]

One common issue with carbon steel RTJ flanges is the material of ring gasket used. What is your ring gasket material? I'd recommend Soft Iron ring gaskets only for carbon steel RTJ flanges, as your ring gasket hardness must be lower than your RTJ flange hardness to effect a good seal.

I've seen many RTJ flange joint leaks as a result of maintenance/engineers not understanding this basic principle.

 

[LittleInch]

At low flow does the pipe temp go up or down?

What loads change between the two?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[r6155]

More information: flange CLASS ??
Is the stud tension the same for both flanges?

I asume that flanges are Welding Neck

Regards

 

[GD2]

OP,
Something is wrong. Why two different pipe wall thicknesses for the same system design conditions?
And what do you mean by low load? Do you mean lower pressure or temperature?

GDD
Canada

 

[A8yssUK]

Hi OP,

Sealing engineer from a gasket manufacturer here. Firstly talk with a decent gasket manufacturer who is a member of the ESA(European Sealing Association) and/or FSA(Fluid Sealing Association) , they know a lot more than just about gaskets

I personally rate Lamons, Flexitallic, SGLCarbon and Teadit very highly for higher temp/pressures systems.

 

[mason6555]

Based on the information provided, there are a few potential causes for the situational leaking you're experiencing with the RTJ (Ring Type Joint) flange on the west side line. Here are some possible failure modes and recommendations:

1. Thermal Expansion and Contraction:
The leak occurring at low loads and stopping at higher loads suggests that thermal expansion might be a factor. At higher loads, the increased temperature could cause the metal to expand, potentially closing small gaps or improving the seal.

Recommendation: Analyze the thermal expansion of the system and ensure that the piping system has adequate flexibility to accommodate thermal movement without putting excessive stress on the flange joint.

2. Pipe Stress:
While the hangers are reported to be functioning properly, there might be residual stress in the piping system that's only evident at certain operating conditions.

Recommendation: Conduct a detailed stress analysis of the piping system, particularly focusing on the differences between the east and west lines.

3. Flange Face Damage:
The flange faces might have minor damage or distortion that becomes more pronounced at certain operating conditions.

Recommendation: If possible, perform a non-destructive examination (NDE) of the flange faces without disassembly, such as using ultrasonic testing or advanced visual inspection techniques.

4. Ring Joint Groove Issues:
There might be damage or deformation in the ring joint groove that's not fully addressed by the new ring.

Recommendation: If inspection is possible, check the condition of the ring joint groove.

5. Differential Thermal Expansion:
The difference in wall thickness between the two pipe sections (1.806" vs 0.556") could lead to uneven thermal expansion, potentially causing alignment issues at certain temperatures.

Recommendation: Analyze the thermal behavior of the joint, considering the different wall thicknesses.

6. Bolt Relaxation:
At different operating conditions, the bolts might be experiencing varying degrees of relaxation.

Recommendation: If accessible, check bolt torques at different operating conditions. Consider using special bolting materials or techniques designed to maintain consistent clamping force across a range of temperatures.

7. Vibration:
There might be system vibrations that are more pronounced at certain operating conditions, affecting the seal integrity.

Recommendation: Conduct vibration analysis at various operating conditions to identify any potential issues.

Given the high cost and low return of disassembly and inspection due to the seal-welded clamp, your consideration of replacing the flange with a tapered wall thickness, solid pipe section is a reasonable approach. This would eliminate the potential for leakage at this joint entirely.

However, before proceeding with this option, it would be beneficial to:

1. Conduct a thorough engineering analysis of the proposed solution to ensure it meets all design and operational requirements.

2. Consider the root cause of the issue to prevent similar problems from occurring elsewhere in the system.

3. Evaluate the cost-benefit of this solution compared to other potential fixes, including long-term maintenance and inspection requirements.

4. Ensure that removing the flange doesn't negatively impact future maintenance or modification capabilities of the system.

Remember, without a direct inspection, these are educated guesses based on the information provided. The actual cause could be a combination of factors or something not listed here. Always consult with experienced engineers and follow appropriate codes and standards when making modifications to high-pressure, high-temperature systems.

Please visit:

https://changyuanflex.com/technical...stallation-tips-anti-vibration-rubber-joints/

for more information

 

[LittleInch]

TLDR this AI word salad....

The jast section is the only bit worth reading.

IMHO.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.