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How many passes are required

How many passes are required

How many passes are required

Dear experts,

Is there any guidance in regards to how many passes (including root, hot and cappings) for lap weld joint and butt weld joint with SMAW process ?

For example :

a. Bottom plate to bottom plate lap joint where the thickness is 10 mm. Let say 2.4 mm for root pass + 1 pass 3.2 mm + 1 pass 4 mm .

b. Bottom plate to annular plate lap joint where the bottom plate is 10 mm and annular is 13 mm.

c. Vertical joint on shell plate 24 mm.

I have seen CB&I has their on standard for the above cases and many other cases.


RE: How many passes are required

Greetings, excuse me, but I am assuming that you are working in a storage tank construction, I submit this paragraphs of API 650 2013:

" The minimum size of fillet welds shall be as follows: On plates 5 mm (3/16 in.) thick, the weld shall be a fullfillet
weld, and on plates more than 5 mm (3/16 in.) thick, the weld thickness shall not be less than one-third the
thickness of the thinner plate at the joint and shall be at least 5 mm (3/16 in.)."

" Weld passes are restricted as follows: For bottom plate welds and roof plate welds for all materials, and for shell-to-bottom welds for Groups I, II,
III, and IIIA materials, the following weld size requirements apply:
a) For manual welding processes, fillet weld legs or groove weld depths greater than 6 mm (1/4 in.) shall be
multipass, unless otherwise specified on the Data Sheet, Line 15.
b) For semi-automatic, machine, and automatic welding processes, with the exception for electro-gas welding in, fillet weld legs or groove weld depths greater than 10 mm (3/8 in.) shall be multipass, unless otherwise
specified on the Data Sheet, Line 15. For Groups IV, IVA, V, or VI shell-to-bottom welds for all welding processes, all welds shall be made using
a minimum of two passes"

" Shell-to-Bottom Fillet Welds
a) For bottom and annular plates with a nominal thickness 13 mm (1/2 in.), and less, the attachment between the
bottom edge of the lowest course shell plate and the bottom plate shall be a continuous fillet weld laid on each
side of the shell plate. The size of each 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 (that is, the shell plate or the bottom plate immediately
under the shell) or less than the following values:
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.
c) Shell-to-bottom fillet weld around low-type reinforcing pads shown in Figure 5.8 Details a and b or around shell
insert plates that extend beyond the outside surface of the adjacent tank shell shall be sized as required by
paragraphs a or b above.
d) The bottom or annular plates shall be sufficient to provide a minimum 13 mm (1/2 in.) from the toe of the fillet weld
referenced in to the outside edge of the bottom or annular plates."

Your WPS should be designed to conform those requirements.Your weld engineer should be carefull with over size welds. Look for ASME section IX the table QW-253 WELDING VARIABLES PROCEDURE SPECIFICATIONS (WPS)
Shielded Metal-Arc Welding (SMAW)

The design of the weld it's going to depend's on referencing code or standard of construction

RE: How many passes are required

Dear II23,

Yes I am working in a storage tank construction.

Thanks for your info.

It is true before starting the work the subcontractor must made WPS to cover all welding requirements.

But during the construction, I found very seldom our welder or welding foreman or welding supervisor fully comply with the approved WPS.

Most of them worked based on their experiences.

I knew it is not the right way but that was and still happened.

RE: How many passes are required

Dear Syahar1975

I worked as the welding engineer more than 10 years,and experience in storage tanks. that is a bed concept and habit for the welder to execute welding working as per his experience aside the WPS .

other reasons why the welder don't welding as per the WPS because the WPS is not very clear or out of practice. The welding engineer must familiar with not only the standard but also the welding operation.

like the circumstance in you question. when Bottom plate to bottom plate OR bottom plates to annular plates lap joint where the thickness is 8-10 mm,I recommend a welding sequence, firstly use the 4.0mm electrode,deposit a fillet size about 4mm in the corner of the lap joint,then use 3.2mm electrode deposit the upper and lower of the first layer to make the fillet size fulfill the requirement.

update some photos for you reference.

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