Temporary Repair Cracked Flange

[SIMONMAGSUCANG]

Dear all,

I have a few heat exchanger flanges found cracked possibly due to over-torqued and victim of hydrogen sulfide stress cracking, the operating temperature is between 45 to 129 deg C.

I can't shutdown the line for replacement, is there any ways to temporary repair these flanges and hold them for at least 1 year until next shutdown? Flange repair clamp sounds like a solution but I'm afraid it will further damage the flange during fastening..

Wish I can have more suggestions...

 

[racookpe1978]

Sure. If there was near-zero internal pressure. And nobody and no regulators cared if (when!) the whole thing fell off of the pipe and you dumped your flaming hazardous and toxic liquid into the river.

Pressure, temperature, operating fluid, pipe metal, flange metal ... Are what?

 

[LittleInch]

Try talking to these guys.

I recall they have techniques, clamps and things to sort most things..

http://www.furmanite.com/

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

 

[SIMONMAGSUCANG]

The temperature is 45 to 129 deg C, pressure is around 10 psia, fluid media is hydrocarbon gas..flanges are made of carbon steel.

Furmanite is one of my consideration, they do offer repair clamps for flanges, but I just need to make sure if this is a good method. According to our corrosion engineers and also vendors, repair clamps are unable to assure a minimum warranty for "cracked" flanges, they can install it for such repair but couldn't guarantee the warranty period. I need something that can temporary reinforce it at least for 12 months until next shutdown, sorry I was unable to provide photo but the cracking is quite severe and extended to the bolt holes..

Has anyone having experience of repairing such cracked flanges?

 

[bimr]

Why don't you post a picture. Worth a thousand words.

 

[MJCronin]

Are you sure that your flanges are carbon steel ? Cast Iron Flanges have a long, long history of cracking due to over torque.

Carbon steel is a ductile material...... and substitution of CS for CI is a common solution

MJCronin
Sr. Process Engineer

 

[SIMONMAGSUCANG]

Hi guys,

Managed to get some photo from my inspector from offshore, please see the attached.
Perhaps you guys can take a look and give some suggestion?

 

[LittleInch]

You say you have "a few HX flanges" Are they all cracked like this?

For me I would simply clamp it with two half shells around the flange outer circumference.

I don't know what the crack mechanism here is, but SCC seems unlikely in this location. That would require some force to split that unless there is a material fault.

Seems a thick flange for 10 psi(a?) - is this under vacuum?

how far does that crack go? Picture from underneath would be good.

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

 

[SIMONMAGSUCANG]

There all total of 4 flanges found cracked, the one that I showed in the photo is the most critical. We suspect due to over-torqued, we are actually taking over one of the oldest offshore gas platforms from another operator and there are a lot of rehab required, we don't even know why there are such defects at the first place after being handed-over the platform, we were not being handled over the inspection reports from the previous operator and now we have to start all over again..

The crack goes quite deep and almost reaches the bolt..

If putting on 2-half-shell clamps or split sleeve repair clamps on the flanges, will it actually causing more stress to the cracks and eventually rupture the flange? My vendor could not give any better justification because not even them dare to give any warranty of at least 1 year.

Another concern is if putting on repair clamp, what will be the recommended tension/torque for the clamps' bolting? The clamp will be secured from outside the flange, over-torque will definitely causing more cracks on the flange, and insufficient torque will make no difference to the repair.. I don't prefer welding on the repair clamp because we need to frequently monitor the flange, and by bolting is able to tighten more flexibly..

 

[LittleInch]

I don't really understand your concern.

There is very little circumferential force on the outside of a flange so any external ring clamp clamp is simply there to stop this crack getting any bigger.

how would the flange "rupture"? When you initially said crack I though this was in the shoulder of the weld or otherwise on the parts inside the bolt circle.

"warranty" will scare off most vendors for something like this. You can only try something and monitor the crack regularly for any changes.

You could just cut a channel in from the outside to the bolt and create a slot. This part of the flange is only really holding the bolts in place and providing a bit of metal for the bending moment caused by the bolt tension, but cutting slots in a flange has very little impact on the strength of a flange.

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

 

[SIMONMAGSUCANG]

Bro LittleInch,

You are right, when I am asking for warranty, all of them back-off from my request..

May I know what do you mean by cutting a channel in fro the outside to the bolt to create a slot? I am sorry I don't get what you mean...can you please kindly explain in more detail?

 

[LittleInch]

like this

http://www.moon-american.com/product_detail.php?pid=126&cat=19

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

 

[Shmulik]

Hi,
As it seems from the stamping on the flange at your pictures, this NPS 12" RTJ flange is made of 304 stainless.
I wouldn’t consider the austenitic stainless steel (300 series) as the best choice for offshore environment……
Cl-SCC usually occurs at above 60°C (and more likely under wet insulation).

 

[SIMONMAGSUCANG]

Thanks bro LittleInch.

Bro shmulik, it is not SS304, SS304 definitely not be suitable in offshore.

You had a point just like MJCronin, CI will be the victom for such cracking occured, and yes it is under wet insulation (it is HX). I will have to check with the inspector once again because the inspection report is presenting it as CS.

 

[Shmulik]

SIMONMAGSUCANG, please recheck the stamping on the flange for the material:

 

[rconner]

[or "304L"?]

 

[SIMONMAGSUCANG]

After checking with inspector once again, the cracked flanges are SS304, however the drawing was stated CS...

Nevertheless thank you very much for correcting me Bro Shmulik.

Trying to convince my boss of using the repair clamp right now..

 

[EdStainless]

No, since these are SS with known chloride stress cracking you tell your boss that the only option is shutting them down for replacement now.
Anything that you do will shift stresses and result in new cracks.
You could make new split rings to put on the outside of both faces, but what about where the flange attaches to the body? Are there any cracks there?
What is the damage/liability when one of these completely fails?

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

 

[Guest102023]

This is no way to do failure analysis. You need to understand both the fracture mechanism and the root cause before contemplating a fix. In the meantime point a portable XRF instrument at the metal.
More significant than the grade stamped on the flange - what is the country of origin?

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

 

[SIMONMAGSUCANG]

Good idea, X-ray Fluorescence is a good method to check the flange material if we do not know what is the exact material... thanks!

There are no cracks at other part, but only on the flanges, double confirmed with inspector offshore. X-ray Fluorescence will be a good suggestion to be first conducted on the flange, then we will move to next step, eg using repair sleeve or etc..