API 650 5.1.5.7 Shell-to-Bottom Fillet Welds, annular plate more than 13does code allow fillet only 2

[Frank Zhang]

5.1.5.7 Shell-to-Bottom Fillet Welds
b) For annular plates with a nominal thickness greater than 13 mm (1/2 in.), the attachment welds shall be sized so
that either the legs of the fillet welds or the groove depth plus the leg of the fillet for a combined weld is of a size
equal to the annular-plate thickness (see Figure 5.3c), but shall not exceed the shell plate thickness.
How to understand this section? Does this section allow fillet weld only.
My understanding is:it has a choice: 1)-fillet weld only, 2) fillet+groove weld combine.
1- b) For annular plates with a nominal thickness greater than 13 mm (1/2 in.), the attachment welds shall be sized so
that the legs of the fillet welds is of a size equal to the annular-plate thickness (see Figure 5.3c), but shall not exceed the shell plate thickness.
2- b) For annular plates with a nominal thickness greater than 13 mm (1/2 in.), the attachment welds shall be sized so
that the groove depth plus the leg of the fillet for a combined weld is of a size equal to the annular-plate thickness (see Figure 5.3c), but shall not exceed the shell plate thickness.
is it right?

 

[Dhurjati Sen]

Tank shell to bottom welds are fillet welds only, as the 5.1.5.7 heading goes.

By groove depth, it is meant whether any edge preparation is done on the shell plate. The resulting weld is a fillet only.

The fillet leg length would be equal to annular thickness as long as it is less than equal to the shell plate thickness.

To put it simply, it is equal to the shell plate thickness as annular is almost always thicker than rhe bottom shell course.

DHURJATI SEN
Kolkata, India

 

[Frank Zhang]

Dear Mr DHURJATI SEN
Thank you for your reply.
My understanding is for example:
If i have a tank, bottom shell thickness is 30mm. annular plate is 20mm.
I have two choices to weld the bottom and shell plate together.
1. I weld 20mm fillet weld inner and outer.20=annular thick.
2. I weld 10mm fillet +10mm groove combine weld both side. 10+10=20=annular thick.
am I right?

 

[Geoff13]

Either weld is limited to 13 mm maximum, so your first option of a 20 mm fillet isn't permitted.

You could do : [ol 1]
[li]a 13 mm fillet plus a 7 mm groove[/li]
[li]a 10 mm fillet plus a 10 mm groove.[/li]
[/ol]

The second option has a slightly smaller weld volume, but you should make your own cost analysis to decide which to use.

 

[JStephen]

I agree with Geoff's answer above.

 

[HTURKAK]

IMO, API 650 standard is more than clear and agrre with GEOFF..

- Look clause 5.1.5.7 Shell-to-Bottom Fillet Welds

- Figure 5.3c—Detail of Double Fillet-groove Weld for Annular Bottom Plates with a Nominal Thickness
Greater than 13 mm (1/2 in.) (See 5.1.5.7, Item b)

I cannot give you the formula for success, but I can give you the formula for failure..It is: Try to please everybody.

 

[Frank Zhang]

Dear all
Thanks for your reply.
I am understanding from your upside reply:
It means for this case annular plate greater than 13mm, shell to bottom weld have no choice, only allow Fillet-groove Weld Right?
But after reading it’s statement, it has conflict.
b) For annular plates with a nominal thickness greater than 13 mm (1/2 in.), the attachment welds shall be sized so that[highlight #A40000] either[/highlight] [highlight #204A87]the legs of the fillet welds[/highlight][highlight #A40000] or[/highlight] [highlight #204A87]the groove depth plus the leg of the fillet for a combined weld[/highlight] is of a size equal to the annular-plate thickness (see Figure 5.3c), but shall not exceed the shell plate thickness.

The phrase either…or…is giving a choice or not? Like below understanding?
For annular plates with a nominal thickness greater than 13 mm (1/2 in.), the attachment welds shall be sized so that the legs of the fillet welds is of a size equal to the annular-plate thickness (see Figure 5.3c), but shall not exceed the shell plate thickness.

Which means it allow fillet weld , and fillet weld size equal to annular plate thickness?
since the 13mm limit is reading from5.3c which is special for fillet-groove weld. is it suitable for fillet weld only?
Thank you.

 

[IFRs]

5.1.5.7
The size of the corner weld shall not be more than 13 mm (1/2 in.) and shall not be less than the
nominal thickness of the thinner of the two plates joined.

If the thinner of the parts being joined is over 1/2" you have a problem.

So solve this problem, you are allowed to cut into the shell and claim that "grove" distance to get to the size you need.