Welding of SS patches on CS roof of Ammonia storage tank based on API 620 R.

[Muhammad Ijaz]

Dear All,

We have an Ammonia storage tank designed on API 620 R. Material of construction for roof, shell and bottom is ASTM A 573 Cl.1 (CS). Min metal design temperature is minus (-)45 deg C and operating temperature is minus (-)33 deg C.
Inspection of roof is done and it is badly corroded along the welds and plates itself.
Now we are planning to apply stainless steel 316 patches over the roof.
1. Please provide any API reference which allows to weld SS 316 patches on CS roof.
2. Please provide code/standard reference or criteria to calculate stress in dissimilar weld of SS and CS due to difference in thermal expansion.

Regards,
Ijaz

 

[HTURKAK]

Refer to API STANDARD 653 ; Clause SC.9 ; Tank Repair and Alteration Revise 9.3 to read: Lap patches shall be made carbon steel to carbon steel and stainless steel to stainless.

I would be hesitant to use SS 316 patches on CS roof and my concern would be accelerated galvanic corrosion.

I would like to hear the thoughts of others on this thread.



Use it up, wear it out;
Make it do, or do without.

NEW ENGLAND MAXIM

 

[MJCronin]

I would like to hear why Muhammed cannot procure thin-walled carbon steel sheets ..

As I recall, a thin carbon steel sheet of about 6 - 8 mm would be adequate ...

Carbon steel sheets are available everywhere ....

MJCronin
Sr. Process Engineer

 

[mk3223]

It seems weird that the patch of the CS tank roof with a piece of the 316SS plate. The CS material is suitable for the Ammonia storage tank.
Some questions for the thoughts:
-How long the tank is in the Ammonia service?
-What's the root causes of the corrosion along the CS plate and welds?

 

[Muhammad Ijaz]

Thank you for your responses.
@MJCronin
We try to find quote of 3mm thk A 537 Cl1 plates but no vendor gave offer.
@mk3223
It is out of service for 25 years. Now we want to take in operation.
Corrosion is mainly due to CUI.

1. Whats wrong to use SS316 on CS roof other than galvanic corrosion?
2. Please provide code/standard reference or criteria to calculate stress in dissimilar weld of SS and CS due to difference in thermal expansion.

 

[dik]

That's a big problem, right there, and not recognising it as one is another big problem.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[HTURKAK]

Muhammad Ijaz,

So you can find SS 316 and dissimilar electrode but you can not find CS plate suitable for lap patches of CS roof . Is this true ?

In this case i am keeping silence . Sometimes silence is gold ..



Use it up, wear it out;
Make it do, or do without.

NEW ENGLAND MAXIM