Single V vs Double V 1

[dursosono]

What the adventage double V than single V for constructed of storeg tank per API 650? I know both of joints are allowed by API 650 and it's not essential variable per ASME-IX. It's horz. & vert. joint of shell to shell. I need suggestion for achieved good result or best practised. Thk shell 8 mm, there are 4 course with diameter 10 m. Welding process is SMAW and will be fabricated on site. How much minimum welder have to used?

 

[IFRs]

The shape of the joint is less important in my opinion than the end result - full penetration, 100% fusion of the plates. Depending on the process (automatic, MIG, sub-arc, by hand, etc), gap, position (vertical vs horizontal) and the equipment the joint could be square, single or double bevelled. For the thickness you have, I'd use square edge plates with a 1/8" gap. The tank builder should have standard practices. The weld proceedure should specify the root gap and joint preparation. The x-rays will tell you how the joints are coming out.

 

[racookpe1978]

Would you expect a (low pressure) plain steel tank 30 m diameter with 8 mm walls to get X-rayed?

Unless its pressurized, I'd figure they call for visual NDE. PT if petroleum and leaks must be prevented - Although he using an API reference, he has not stated his liquid.

Or am I wrong in my assumptions?

 

[IFRs]

Please see API 650 sections 7.3 and 8 for inspection criteria. If you are building an API 650 tank it should be inspected in accordance with API 650 no matter what it is holding.

 

[stanweld]

Double V grooves are used to reduce the volume of deposited weld metal on heavier wall thickness cost savings) and "balance" welding residual stresses. For groove welds in 8 mm thick plate, single V bevels are used.

 

[hogan666]

The main differences are in regard to heat input and distortion. At 8mm there is not a lot of advantages.

 

[vesselfab]

If you single bevel the shell plate and weld from one side, and then arc gouge or grind to sound metal on the other side , then you have a double V weld.

even though you bevel from one side, and then make a grove on the other by mechanical means, it's still a double V weld.

it's a lot easier than trying to put in a perfect root pass for x-ray purposes.

 

[Dinosaur]

I agree with Stanweld

 

[valkyrie77]

Single V grove weld can used here because it is possible to finish the weld in 2 passes, which is the same as double V. I am using Rapidarc process (mechanised, forced short arc), to do it in 1 pass. It provides good surface appreance+good welding & metal properties...

 

[Ballbearing1]

vesselfab,
Hope this doesn't sound pedantic but if you backgouge it is not a double vee but a single vee, single U combination.
Nobody ever says that because it is always called a single vee with backing, single vee with backgouging or single vee with backgrinding.
If you grind a double vee prep and weld from one side you will still need to gouge / grind the backside anyway.
Regards,
BB

 

[HgTX]

"if you backgouge it is not a double vee but a single vee, single U combination"

AWS disagrees.

Hg


Eng-Tips policies: faq731-376

 

[vesselfab]

Well, I was always under the impression that it doesn't matter how you get the bevels there or the backing.

if during the course of welding, you get bevels on both sides, mechanical bevel one side and gouging/grinding the other side....it was considered a double v weld.

a single v is when you leave the root in and only weld from one side.

but I've only been doing this for 40 years and things change
in terminology.

 

[hogan666]

vesslefab,
AWS A2.4 should clear up any confusion you have.

 

[HgTX]

Look at AWS D1.1-08 page 96, prequalified joint detail B-U3b. Double-V with backgouge. Contrast that with page 100, detail B-U7. Double-U, with backgouge, but also with requirements for the radius of the bottom of the U.

Hg


Eng-Tips policies: faq731-376

 

[vesselfab]

I DON'T REALLY KNOW WHERE ALL THE U GROOVES CAME FROM

AND I UNDERSTAND SYMBOLS

What i was trying to say is if you make another bevel on the second side of welding, no matter how you get it there,
it's a double v weld.

that's all

 

[HgTX]

Jeez, no need to scream.

V vs. U depends on the shape. Ballbearing1 was saying that if you backgouge, you make the back "V" a shape with a rounded rather than pointed tip, which means it's a U rather than a V and so technically the joint's not a double V. I'm saying (mostly to Ballbearing1, since that's who's making the claim that I quoted) that AWS still considers it a V, as evidenced by the D1.1 figure I cited. I suspect their distinction is a matter of tip radius.

Hg

Eng-Tips policies: faq731-376

 

[DVWE]

I don't know how this got off track, but hogan666 is correct. See attachment from AWS A2.4 regarding this issue.

 

[DVWE]

B3.19 gives the explanation. If calling the joint out with symbols, this is how you do it.

 

[DVWE]

As I read Ballbearing1's post, he is exactly right in his explanation.

 

[vesselfab]

Ok

you were speaking of the bevel configuration

Guess I should have said....doulble side weld and not a single sided weld

either way....non=essential....to me a bevel is a bevel

ok guys

proceed