Ammonia vessel: Base material vs Electrode type

[jhg]

Hi,

1)Does anybody know about an existing A-516Gr70 ammonia sphere welded with E 7018 G electrode?
2)I need to find technical reasons to defend E 7018 series electrodes instead of E 8018 series for this type of vessels in order to avoid stress corrosion cracking.

Any information you could give on this regard will be very helpful.

Thank you

 

[Norphlet]

http://www.hobartbrothers.com/product/index.cfm

Under technical page, there are 7 pages. Hit page 4 for A516.

ASTM: A516
ASME: SA-516
Grade: 70
UNS number: K02700
Specification: Pressure Vessel Plate, Carbon Steel
Minimum Tensile Strength: 70 Ksi

ASME/AWS SMAW Welding Specification: SFA-5.1
SMAW/AWS ClassifiCation: E7018

ASME/AWS GTAW/GMAW Welding Specification: SFA5.18
GTA/GMA AWS ClassifiCation: ER70S-3

 

[twjag]

E70XX electrodes are correct for SA516-70.
Stress corrosion cracking occurs in the HAZ, not in the weld, for vessels in anhydrous ammonia service. This is why many jursidictions require PWHT for ammonia service, except for aqua ammonia. I have not seen any literature indicating that E80XX electrode have an advantage over E70XX for these conditions.

 

[jhg]

I agree about the correct choice of E70XX for SA516-70.
I also think that using an E80XX electrode is not adequate as there would be big difference between mechanical properties of base material and the electrode. It could happen that the electrode yield strength is higher than the base material tensile strength!

It would be very helpful for me if someone could send me technical docs on this regard or how to find it.

 

[twjag]

Check out following link:

http://www.nationalboard.org/Classics/classic28.html

A number of hits were found by searching "ammonia weld crack" on web.