Repair against Chloride SCC in Tank 1

[RogerSAM]

Hello everyone,

We are currently facing an issue in our urea manufacturing plant. We have observed severe external chloride SCC in a carbamate solution tank. Design data is given below, and pictures of the cracks are attached for reference. There are currently two limiting factors:

1. Although we have recommended its replacement as soon as possible, but the logistics and planning are not allowing it to be replaced until 2-3 years later.
2. Wherever we attempt a repair, more cracks appear in the welds' HAZ.

I wanted to inquire if any of you have faced a similar problem and if so, what repairs can I undertake to ensure its safe operation for 2-3 more years?

Design Data
DP = 285 PSI
DT = 100 C
Service = Ammonia, Urea and Carbamate
Material = A240 Gr. 304L
Shell Thickness = 5mm
Bottom Plate Thk = 6mm
Design Code = BS 2654

 

[EdStainless]

There is no fix.
Tell planning that this tank will have to be taken out of service within a short period of time when it fails.
See how that impacts their plans.
You can clean and grind all that you want to.
But the stresses from the new welds will drive more CSCC.
If you needed to get a few months then there might be options.
Design a replacement tank in duplex and get it on order this month.
The duplex tank will be a bit thinner because of the higher strength.

 

[weldstan]

Agree with Ed, there is no weld repair fix and there is no potential repair non welding fix that will last for 2 to 3 years..

 

[dgeesaman]

Planning should have their desks moved next to it if they think something like this can be milked for 2-3 years.

 

[r6155]

a) Obviously I agree 100% with the comments above
b) But let me tell you an alternative:
Weld the pad over the area and perform an Acoustic Emission Test (see ASME V) after this and every 3 months.
The pad with a 1/4" NPT hole to detect leaks.

 

[SJones]

The weld for the pad attachment will also be prone to cracking. The cracking is from the outside inwards. If the depth of cracking has been fully characterised, and is believed to be shallow (don’t ask how shallow - what depth of cracking deemed salvageable is another risk factor consideration), quality application of a coating may serve to prevent replenishment of the cracking environment buying you the time to get a replacement manufactured. Thermal spray aluminium would be the best choice if economics pan out. Acoustic emission testing would be a supporting activity.

https://onepetro.org/NACECORR/proceedings/CORR07/All-CORR07/NACE-07476/118625