Absorber tower repair with Alt PWHT 1

[metalhoosier]

I have an absorber tower where an MDEA amine solution is part of the process stream. Repair welding (fillet welds) is needed on the ASME pressure vessel. Almost every document I have researched instructs PWHT to be performed after repair welding. The material is 15/16" SA-212-B plate and the repairs are at the bottom of the tower. I'm concerned about buckling the tower at an 1100F PWHT temp. Has anyone here had luck with reducing the residuals stresses of the these type of repairs in an amine enviornment sufficiently using the NBIC's Alternative postweld heat treatments? (method 1 or 2)

Metalhoo

 

[metengr]

Yes. The increased preheat for Method 1 is ideal for this repair scenario. Make sure you adequately soak the repair area and maintain during welding. Verify acceptance of the weld repair using wet fluorescent MT,

 

[metalhoosier]

Metengr,

Thank you for the quick response. Are you aware of any research papers that have proven this Alternative PWHT method successful with amine solution using ASTM E837?

 

[metengr]

metalhoosier;
I have a number of colleages that are petrochemical and from years of working with them on various codes and standards committees, I have never heard of an issue using this method for field repairs of petrochemical vessels.

There is another method, and this is also referenced in the NBIC. Local PWHT using a circular band for PWHT as defined in Part 3. This method was developed using the information defined in AWS D10.10.

You might also want to consider a temper bead approach and here EPRI has conducted extensive work on the qualification of this method. The grain refinement in the base metal HAZ from this technique results in increased toughness from original base metal toughness properties (especially for the lousy toughness of SA 212 plate material). You can qualify the temper bead repair method using Section IX and evaluate hardness data as part of the qualification.

 

[metalhoosier]

Metengr,

Thank you again for the feedback. Please understand my hesitancy to use this alt. PWHT.

As stated in Part 3 2.5.3 b)"Competent technical advice shall be obtained from the manufacturer of the pressure-
retaining item or from another qualified source, such advice being especially necessary if the alternative is to be used in highly stressed areas, if service conditions
are conducive to stress corrosion cracking..."

This was my red flag to do more research. I understand it also states the above for creep range components, of which I have some experience and we deal with very well, but the amine SCC issues, not so much.

Also, per the API 939-B 2002 document, Repair and Remediation Strategies for Equipment Operating in Wet H2S Service, It was my understanding that the temperbead process proved to be of no benefit in reducing the presence of cracking in the attachment welds. Therefore, we are not looking at this welding process.

 

[metengr]

metalhoosier;
I fully understand your cautiousness. What about using local PWHT (bulls eye) as I mentioned above. This will knock down the hardness in the base metal HAZ and reduce residual stresses. Did you review this local PWHT practice in the NBIC? It is not a band it is a circular heating region, similar to a bulls eye.

 

[grampi1]

Union Oil Lamont - Look it up

http://www.twi.co.ir/download/case_studies/180 - Union oil amine absorber tower.pdf

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