Water tank welding procedure

Question

Water tank welding procedure

beercia (Mechanical)

(OP)

9 Jan 04 15:10

I have a question related to a welding procedure for welding the wall shell plates for a small 4000 BBLs water tank. Material of the wall plates is ASTM A36 1/4" thick 3 by 6 ft and the welding procedure calls for using welding electrodes A6010 for first pass and then A7018 for second and later passes. The thing is the contractor wants to change the A7018 electrode for the A6010 for the remaining passes. What effect could have this on the strength of the joint, finished quality and anything detrimental to the soundness of the joint and the tank itself. Is it OK to make the change? Which is a more appropiate welding electrode to use in this case: A6010 throughout or both A6010 and A7018?

Rich2001 (Mechanical) · Answer 1 · 2004-01-09 15:55:16

Required Mechanical properties per AWS F5.1

6010   Tensile Strength 60 ksi
       Yield strength 48 ksi
       Elongation in 2 in. 22%

7018   Tensile Strength 70 ksi
       Yield strength 58 ksi
       Elongation in 2 in. 22%

Other than the yield and tensile strength differences the storage of the electrodes is different.

While 6010 can be stored at aambient temperature 7018 should not be.

7018 will pick up moisture from the atmosphere that can cause hydrogen cracking after welding. Therefore the elecrode are stored 50 to 250 F greater than the ambient temperature.

deanc (Specifier/Regulator) · Answer 2 · 2004-01-09 17:21:13

Don't see a problem if the welders are qualified. 7018 has a smoother cap. Suggest a 6010P5 or a P+P,runs better.

JoeTank (Structural) · Answer 3 · 2004-01-09 18:08:33

Also poste in the API forum...

Good news... Strength-wise, E6010 (60ksi tensile strength) is adequate for ASTM A36 (58ksi tensile strength).

Bad news... E6010 (F3) and E7018 (4) are different F number electrodes, so this is a change in an essential welding variable. A requalification of the welding procedure will be required.

Steve Braune
Tank Industry Consultants
www.tankindustry.com

GRoberts (Materials) · Answer 4 · 2004-01-09 23:41:37

First check the qualification record. If it was in accordance with ASME IX, then to weld the 1/4" thick plate with 6010 electrode, it would be ok if the original qualification had at least 1/8" thickness of 6010 deposit. (ASME allows qualification up to 2T on material less than 1 1/2" thick). If it is qualified properly, you will probably not have a problem using 6010 on such thin material. The main problem with 6010 is the cellulose in the coating contains moisture, which can cause hydrogen assisted cracking under certain conditions. However, the thin material makes the chance unlikely because it will cause less restraint and will not cool of the weld as fast as thick material. However, if the thin walls are welded to a thicker floor or other tank features, think about sticking with the low hydrogen electrodes (7018) for those welds.

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Water tank welding procedure