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Phthalic Anhydride (PA) plant Ageing Drum corrosion problem

Phthalic Anhydride (PA) plant Ageing Drum corrosion problem

Phthalic Anhydride (PA) plant Ageing Drum corrosion problem


We observed a leakage in the shell of Ageing Drum Phthalic Anhydride (PA) plant.
After inspection of inside of Carbon Steel material shell, severe corrosion can be also seen in other areas. I consider that phthalic acid occured and metal corroded.
Operation team indicates that there was not any improper operation and operation temperature is 270C. So, they say that there is no water and acid formation.

What is the reason of this corrosion in Ageing Drums? Do you have experience or knowledge?

Best Regards,

RE: Phthalic Anhydride (PA) plant Ageing Drum corrosion problem

How old is the drum ? Is it an ASME (or other certified) Stamped pressure vessel ?

What are the dimensions, wall thicknesses, specific material of construction ? How is it supported ?

Is the component subject to pressure/temperature transients ? .... Operations claimed "no acid ever formed"... Was the unit started up and shut down ever?

Are there any design drawings, plans or datasheets available ?.... or were they discarded by the previous plant owner management ? ...any records of repairs ?

Nothing lasts forever .... not even love, but ....

Now would be a good time to get a price on a replacement unit .... However, you can't even do that if you have no drawings, no datasheets, no records, no operational history and you have no history of repairs ...

You could get a couple of estimates for a replacement unit.... perhaps one estimate a more corrosion resistant material. You could also get an idea how many weeks/months it would take to get a replacement unit fabricated

Can you post pictures ?

You say severe corrosion .... Do you want to call in a specialist

Sr. Process Engineer

RE: Phthalic Anhydride (PA) plant Ageing Drum corrosion problem

Drum is not old. A285 GrC material with 8mm thickness.
It was built in 2014 and not expected corrosion in such short time. Before this drum, former drum worked 35 years and corroded internally and externally and renewed in 2014. I do not have detailed information. I also consider improper shutdown and startup operations.

We are washing drum now 20% Caustic solution to clean PA from shell of drum and inspect metal surface closely.

RE: Phthalic Anhydride (PA) plant Ageing Drum corrosion problem

Dear erkuts,

Is there a possibility of a jet ejecting from h3 & 49, like there is a failed gasket or a loose bolt?

From the history of the earlier vessel and also taking into account the present operating conditions, 'erosion' is very probable.

We had an issue at the top of an amine regeneration column (A 516 Gr 60, 8 mm thick) some 20 years back where the gasket of the inlet distributor had failed due to poor workmanship, etc.


Kolkata, India

RE: Phthalic Anhydride (PA) plant Ageing Drum corrosion problem

We detected many pitting corrosion areas after cleaning solid Phthalic Anhydride layer and consider this layer causes under deposit pitting corrosion? What is your opinion?

RE: Phthalic Anhydride (PA) plant Ageing Drum corrosion problem

I would focus on that it has operated for 35 years and renewed and corroded recently.

Q1) Have you applied caustic washing before as well? (Before the pitting found)

Q2) If yes, have you checked caustic corrosion?

In order to find the root of corrosion properly, you may carry out failure analysis (ex., replica) to check the pit's composition to find where they came from.

Lee SiHyoung,

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