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Single V vs Double V

Single V vs Double V

Single V vs Double V

(OP)
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?

RE: Single V vs Double V

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.

RE: Single V vs Double V

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?

RE: Single V vs Double V

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.

RE: Single V vs Double V

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.  

RE: Single V vs Double V

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

RE: Single V vs Double V

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.

 

RE: Single V vs Double V

I agree with Stanweld

RE: Single V vs Double V

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...
 

RE: Single V vs Double V

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  

RE: Single V vs Double V

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

AWS disagrees.

Hg
 

Eng-Tips policies:  FAQ731-376: Eng-Tips.com Forum Policies

RE: Single V vs Double V

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.

 

RE: Single V vs Double V

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

RE: Single V vs Double V

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: Eng-Tips.com Forum Policies

RE: Single V vs Double V

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

RE: Single V vs Double V

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: Eng-Tips.com Forum Policies

RE: Single V vs Double V

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

RE: Single V vs Double V

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

RE: Single V vs Double V

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

 

RE: Single V vs Double V

Hello guys,
Sorry if my statement regarding U versus V was misconstrued and after reading B3.19 it looks like I was wrong all along (based on D1.1).
When qualifying welding procedures for the Australian coal mining industry to AS/NZS 1554 Pt 1 the predominant application is crack removal.This will be either a single U (plate partially gouged from 1 side) or double U (plate gouged from both sides).
Where I was getting confused is in the pre qualified section a single vee joint welded both sides with backgouging is shown as a symbol with V below the line, U above the line and backgouging in the tail.
Regards,
BB

RE: Single V vs Double V

BB,

Your first post made perfect sense to me, maybe you meant something else by it???

RE: Single V vs Double V

BB seemed to be saying at first that if you start out with a double V prep but backgouge the back side, then it's not really a double V but a V +U combo because the backgouging created a rounded bottom to the prep.  But that's not how AWS sees it; they base the symbol on the initial prep.

Vesselfab was saying that if you have a single-V prep all the way through (minus land) and then backgouge, that's still considered a double V, not single V (or V + U, whatever).  That's also not the case, per AWS.  Check AWS use of backing weld symbol.

Not that any of this has to do with the OP.

Hg

Eng-Tips policies:  FAQ731-376: Eng-Tips.com Forum Policies

RE: Single V vs Double V

BB was initially talking about a Single V groove.  After backgouging, it becomes a Single V - Single U combo.  Which is correct per the attachment I provided, B3.19.  He then went on to say that no one calls it that, which is correct again, as further explained by the attachment.  To me, in his last part, he was just reiterating that you will have a similar situation with a Double V.

RE: Single V vs Double V

Thanks DVWE,
Obviously I didn't explain it too well.
Regards,
BB

RE: Single V vs Double V


HgTX,
I was purely trying to explain my difference of opinion based on vesselfabs statement below.

"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."

If you have a single Vee weld backgouged the detail on the drawing will show a single vee with backgouging in the tail.
This then becomes a single vee / single U combination but nobody calls it that.They will call it a single vee with backgouging but what shape have you created with the backgouge - a U shape.(Unless you are an experienced operator and can create a V shape prep)
Hope that has explained what I was trying to say.
Regards,
BB
 

RE: Single V vs Double V

Ballbearing1,
I have to agree with HgTX. What you are saying may work as a visual aid. But it is not a correct description of the joint detail. It is non standard. Somewhat like referring to the GMAW process MIG. The majority of people will be able to figure out what it is you are trying to say, but you will also have some that have no idea what you are saying.

RE: Single V vs Double V

You guys are beating a dead horse.  BB has already stated that no one calls it that, but his description is correct.  hogan666, see the A2.4 that you suggested, and they basically describe it exactly how BB does.

RE: Single V vs Double V

some horses need to be beaten after death, if the point is still not taken.

RE: Single V vs Double V

hogan666,
You are beginning to sound like my ex-wife.
As stated in my original response a single vee backgouged is not a double vee weld but a double sided single vee with backgouging.
I may not have explained it clearly but I think we should agree to disagree, there is not much left of this horse to flog !!
Regards,
BB

RE: Single V vs Double V

hogan666,

Take a look at B3.19 of A2.4 and tell me how that is not exactly what BB said in his initial post.

I am putting away my beating stick now!

 

RE: Single V vs Double V

hogan has left the building, dragging away the carcass. It's my horse and if I can not beat it in  public, I will take my toys and go home.   

RE: Single V vs Double V

ok guys....leave the poor horsie alone


but


if i have a double beveled in advance v joint

weld on side

backgouge the other side

does it become a u groove on the other side??

 

RE: Single V vs Double V

vesselfab,

No it does not.  Read the attachment I provided a few posts up.  It explains it perfectly.

RE: Single V vs Double V

DVWE,
It's your horse now

RE: Single V vs Double V

hogan666,

We still love ya, man! [bigsmile}

 

RE: Single V vs Double V

Sorry bigsmile

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