Through thickness crack on Inconel 625 Forged Flange

[Ishack]

Dear Experts,

It is very strange that one of the small bore flange made of Inconel 625 forged (ASTM B564 UNS 6625) got a through thickness crack just near the tapering portion of a flange. The crack was noticed while performing the hydrostatic test. The thickness at the bevel end is 5 mm and the crack was just 25 mm away the GTAW weld. we are currently investigating the failure.

Expert's view and suggestions based on rich experiences will help us to find the real root cause. What could be the reason for such a material failure that too in forged flange of MOC UNS 6625?.

 

[SJones]

Is the manufacturing procedure in accordance with the qualification technical report of NORSOK M-650/ISO 17782?

Steve Jones
Corrosion Management Consultant

http://www.linkedin.com/in/drstevejones

All answers are personal opinions only and are in no way connected with any employer.

 

[EdStainless]

I would start examining the forge procedure for forge reduction ratio and start and re-heat temps, along with how those temps are controlled and verified.
There was no penetrant inspection required?

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P.E. Metallurgy, consulting work welcomed

 

[Dhurjati Sen]

First step is to check the material by chemical analysis and not by PMI.

DHURJATI SEN

 

[cap1a79]

Tapering, hydrotest...These would be the keywords...

Check whether there is sufficient thickness kept after tapering. Generally, tapering, which is to reduce stress concentration by placing in elastic zone of stress & strain curve, could induce thickness reduction over threshold limit.
Conversely, if its thickness is sufficient, make sure that the stress concentration has not crossed the elastic zone.


If the crack happened during "hydrotest", it would not be an issue of corrosion resistance but strength itself.




SiHyoung Lee

 

[gerhardl]

Possible causes:
1. Material impurities: flange or welding materials
2. False manufacturing procedure : forging, welding, annhealing, tempering
3. Failing or not thourogh enough inspection
4. Mechanical forces larger than allowed: bolting torque, bending flange force, missing pipeline support.
5. Pipeline externly loaded, used as ladder or weighted otherwise.

Normally such faults will start as an impurity in the material (point 1 and/or 2) followed by 3, often enlarged or occuring by 4 and 5. The rest is analysis and recheck.

You should also check if this is a one-time or systematic failure influencing other flanges.

 

[MJCronin]

What country was the flange manufactured from ?

MJCronin
Sr. Process Engineer

 

[mfgenggear]

do standard weld repair, and NDT to verify removal.

 

Expert's view and suggestions based on rich experiences will help us to find the real root cause.

The interweb is not very good at those things. Just saying.

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."

 

[mrfailure]

If you really want to get to the root cause, then you need to include a metallurgical failure analysis of the flange. I would also want to note that the fact that the crack appeared during the hydrotest does not mean it formed from the hydrotest. It may have already been present but opened under the pressure. Finally, you note the crack was "just" 25 mm from the GTAW weld, but that 1-inch distance likely would put it out of the heat affected zone.

 

[mfgenggear]

Weld cracks are frequent and have to be radiographic inspected. Before and after a repair.