Overlayed Flanges Cracking under Hydrogen Service 3

[GD2]

Dear Members,
I have a situation where the root of the groove of the Class 2500 overlayed flanges is cracking under hydrogen gas service. The propagation of cracks in the base metal in some cases are more than 4 inches.
Have anyone faced similar problem and the possible remedial action taken for this?

GDD
Canada

 

[RJW000]

What is the material of the base and overlay? Operating temperature? Do you use controlled bolting practices?

Did you consider sending the flange to a lab for a failure analysis? Are you going to do weld repairs? PWHT? Hydrogen bakeout?

 

[MJCronin]

Can you show us pictures ? What is the operating pressure ?... What is the design pressure ?

Was the component weld repaired and what was done to prevent recurrence ?

"Hydrogen gas service" is a little vague ... Can you provide more specifics about the nature of the transporated gas ?

Please tell us more and you will get beter quality answers !!!!..... good luck !!!

MJCronin
Sr. Process Engineer

 

[GD2]

Sorry guys. Here is the operating data:
Flange: Base metal C-0.5Mo, 316 overlayed.
Hydrogen gas Pressure: 2000psig@425 degree C.
Part of Hydroprocessing Unit.

The easiest remedial action was to replace the flanges but I want to know, if others have faced similar problem and the remedial action done to avoid these flanges from HTHA failure. It's the flange groove failing under HTHA cracking, most likely due to high stress in the gasket groove.

GDD
Canada

 

[weldstan]

I've seen thermal cycling induced cracking of the SS overlay and cracking in 2 1/4 Cr-1 Mo hydrocracker shells and flanges. Once cracking occurs in the overlay, hydrogen cracking would be expected in C-1/2 Mo at the operating conditions. You need to alloy up from C-1/2 Mo.

 

[Guest102023]

Hydrogen gas Pressure: 2000psig@425 degree C

2000psig must be the total pressure; what is the H2 partial pressure? Anyway, those are hot and heavy process conditions, as I would expect for a hydroprocessing unit.

I can't speculate on the failure mechanism, although I have one or two guesses. Take it to a met lab ASAP for a proper failure analysis. The metallography alone will tell the story.

As an immediate safety issue, you must scrap and replace any ½ Mo steel as soon as you are able. It is particularly prone to graphitization and is now considered unsuitable for hydrogen service. It has been out of favour for a few decades.




"If you don't have time to do the job right the first time, when are you going to find time to repair it?"

 

[Guest102023]

Disturbing questions are coming to mind:

1) In Canada, August does not usually fall within shutdown season, so was this an unplanned outage?

2) This issue should be getting attention at the highest level in your company. Is it? Escalate this matter immediately if not already done.

3) Not casting aspersions on your abilities, but you were asked to perform a task for which you were not trained. Where is the company metallurgist and/or welding engineer? There should at the very least be a corporate metallurgist available, or failing that, a local one on retainer.

4) The entire vessel (or pipe spool) needs closer examination wherever this cladding arrangement is found. Actually, all welds on ½ Mo steel should be considered suspect until definitively proven otherwise. The very long service time at the conditions you quote are sufficient to condemn it. I'm not sure how detectable incipient decarburization is anyway (I will assume it is that).

Decarburization characteristically unzips in the heat-affected zone of a weld.



"If you don't have time to do the job right the first time, when are you going to find time to repair it?"

 

[MJCronin]

brim....

"Not casting aspersions on your abilities, but you were asked to perform a task for which you were not trained."


Boy ... We have NEVER encountered that on eng-tips before ? eh ?....

MJCronin
Sr. Process Engineer

 

[GD2]

Hi All,
It’s actually the reactor effluent piping flange that is cracking, not the vessel. I am sorry, I don’t have the H2 partial pressure info.

GDD
Canada

 

[weldstan]

C-1/2 Mo is still "unsuitable" for the service as per brimstoner.

 

[Guest102023]

But hopefully that means the scale of the problem is less.

Actually I can’t see this having been a preferred material of construction for the main vessel, even before the issues with ½ Mo steel came to light.

"If you don't have time to do the job right the first time, when are you going to find time to repair it?"

 

[GD2]

Ok. Guys. Thanks to all for your inputs.

GDD
Canada