ASME Pressure Vessel Flange replacement

[Inspector00000008]

Hello everybody,
We have a problem with the inlet nozzle flange of an ASME pressure vessel. After severe corrosion was discovered during the vessel inspection. Welding build-up repair was employed but it generated many many tiny cracks all over the RJ flange face.

Up on so we proposed replacement of the entire flange. The manufacturer's WPS of the old welding joint is still available. The process used then automatic SAW+ SMAW.

The questions are: Is it practically easy to achieve this suggestion(flange replacement)?
What could be the risks to take into account with this suggestion?
Does ASME BPVC accept the change of WPS from the original without design calculations redoing?

Any other comments/tips from experts are welcome!
Thank you

 

[mk3223]

Were the root causes of the corrosion clear, as well as the tiny cracks on the RJ flange due to the welding build-up?IMO, the vessel may be in the risk again during the nozzle flange replacement if unclear of the causes whatever damaged to the vessel.

 

[Dhurjati Sen]

Dear Inspector,

The flange can be replaced.

Carry out a hydrogen bake out at the flange location.

Cut the flange.

The welding location is to be made very clean using power brush / buffing.

Liquid penetrant test is to be carried out on the bevel ends before welding to ensure the absence of cracks.

Include a preheat in the new WPS (GTAW / GTAW + SMAW).

Get the repair certified by an API 510 inspector.

Regards.

P.S. If this is a case of localized corrosion, flange replacement would solve the issue. However, I expect that you have already carried out an internal inspection of the vessel and are pretty sure about its integrity.



DHURJATI SEN

 

[Inspector00000008]

Dhurjati Sen (Materials)
mk3223 (Mechanical)
Thanks for the comments guys,

TO make things clearer:
Shell material : A516 Gr 70
Inlet nozzle and flange: A 350 LF2.
Faulty flange: 24'' Class 600 WN RJ. Thk: 17.45 mm

In fact corrosion attack has very long history in this location of the vessel (the inlet flange face). However,such causes of this deterioration is not clear enough. I am not a corrosion specialist but it could be caused by the high moisture content of the gas medium at the inlet of the vessel. (the vessel acts as a gas dryer and it hold molecular sieve media for this purpose).

Regarding the discovered flange face tiny cracks,They happened after the flange face was weld-build-up repaired. The causes could be the high thickness of the flange , inadequate temperature control pre and during welding build-up, or hydrogen cracking. The attached photo shows samples of the crackings.

Dear Dhurjati Sen, How much time and temperature would you suggest for hydrogen bake out time?... (Thickness at the flange welding joint is 17.45mm.)

 

[Dhurjati Sen]

Dear Inspector,

I was expecting you would mention the service temperature and pressure. I guess the service temperature is quite low as the flange is LF2, else it could easily have been A 105.

Anyway, to answer your specific question, I personally prefer the bake out at 250[sup]0[/sup]C for 4 hours.

However. the general practice is 350[sup]0[/sup]C for 2 hours. (People do not give much thought on the blue brittleness / dynamic strain aging of CS).

Regards.

DHURJATI SEN

 

[oknow]

As I know to keep the integrity of the ASME Mark and certification the repair must be done in accordance with the NBIC. If not the ASME Nameplate/Stamping must be removed and therefore no long a ASME Vessel. If registered with the National Board they shall be notified.

If this vessel is insured at the location then the Insurance Company shall be notified of this repair activity for their concurrence. The Insurance Company may not continue insurance or raise their price 10 fold if they find out the vessel has had any welding done without following the NBIC.

 

[Inspector00000008]

Operating temperature & pressure are 300 C and 45.5 kg/cm2.

I am still wondering, hydrogen bake out process is not very common with the base metals to be welded. I have not even seen it mentioned in WPSs before. Mr Dhurjati Sen, Do you think its necessity differs between different grades of steel?
Do you think hydrogen cracking is probably the main reason behind the flange cracks???

Mr oknow (Mechanical), sometimes repairs to pressure vessels are done in accordance with API 510 inspection code requirements.
Do you think lack of attention to NBIC requirements damages the ASME certification of the pressure vessel?
What would you think NBIC requires in the repair?

Regards,

 

[marty007]

Repairs performed in accordance with NBIC with an R-stamp provide an assurance that the work was performed under an approved quality system and that an AI has witnessed the repairs.

Without these assurances, there's no way to know if an unqualified welder touched the equipment, potentially doing real harm to the materials.

 

[r6155]

If corrosion is in the inlet nozzle flange then change the material.

Regards
r6155