Welding process (SAW)

[fakhfakh]

Dear Sirs,

I've performed a PQR with SAW process for butt weld joint of plate ASTM A 283 GrD thickness 25mm with root face 16mm with two single pass.
Electrode used: SFA 5.17 F7A6-EM12K Dia. 4mm

Results of tests OK

Is it conventionnal to use the above joint design (with 16mm root face) for carbon steel?

Regards

 

[metengr]

Could you please explain your definition of root face? Also, what type of weld joint design did you use for the PQR - single vee, double vee??

 

[stanweld]

Assuming that yours is an X-Groove (double V)design, the maximum face per AWS D1.1 "Prequalified joints" is 1/2-inch for SAW. Depth of penetration coupled with the profile required to produce the two pass weld joint in 1-inch thick material may prove detrimental in production welding.

 

[weldtek]

fakhfakh,
Do you mean that you beveled the plate each side approximately 4.5 mm, or 9mm from one side? Did you back gouge? What Code are you working to?

 

[metengr]

To add to Stanweld's post, if you have a single-vee groove welds, welded from both sides, the recommended root face dimension for SAW on base materials 1/4" to 1-1/2" (6.3mm - 38mm) should be 1/8" to 3/8" (3mm – 9.5mm) respectively. 16mm is too large.

Thus, for carbon steel 25mm (~1") in thickness, the root face dimension should be closer to 8mm (5/16") instead of 16mm (0.63").


I have seen a maximum 5/8" (16mm) root face dimension only used for a square groove weld with backing. However, this is the limit and on thicker material, bevels are required.

 

[SJones]

What is the actual applicable welding code? Apologies if I'm slow, but the standard being applied has not actually been quoted in the question.

Steve Jones
Materials & Corrosion Engineer

http://www.pdo.co.om/pdo/

 

[fakhfakh]

Thanks for all.

The joint design is double V (X)

Applied Code is ASME VIII Div. 1

What is the problem if all the tests and exmination results (RT, UT, Tensile, Bend, Hardness, Impact) are satisfactory?

I've made a sample with square preparation 25mm thickness without any bevel with the same material and the test results are acceptable.

 

[metengr]

There is no problem, as long as you had qualified the weld procedure in accordance with ASME B&PV Code, Section IX guidelines. The comments above deal more with production issues using such a large root face dimension.

 

[stanweld]

To prevent hot cracking, as a general rule of thumb, the width of the face of the weld should be greater than the depth of the deposited weld bead. Narrow bead profiles produce greater residual welding stress, which could induce cracking. Qualification on a 12" long coupon of A-283 D, which generally has a very low carbon equivalent, may not translate well when welding higher carbon equivalent materials and similar materials with substantial longitudinal weld length.

 

[weldtek]

In my experience relying on weld penetration as a means to acheive sound metal through the entire joint thickness can be risky. I recall a job where we welded 3/8" thick carbon steel with a square butt joint. Our preliminary tests showed that we were getting full penetration, x-ray quality welds, however, in production we found something quite different. It became evident that the location of the wire relative to the joint, is extremely critical. Just being off the width of the wire was enough to cause incomplete penetration. My advice is to proceed with caution. From your first post it seems you are at or approaching the limits imposed by QW 403.9 ie. pass > 1/2".

 

[fakhfakh]

I draw your attention that I've used the couple SFA 5.17 F7A6-EM12K for welding which assure a good toughness results.

Values reached about 140J at 0°C

Regarding the position of the wire, the welding machine is equiped with an automatic regulation system. No possibility to go away from the joint centre. Adding to that wed increase voltage in order to have a large intersection at the weld toe.

 

[weldtek]

Looks like you've worked through the details pretty thoroughly. How were you're HAZ impacts? Are you as welded or PWHT'd.

 

[fakhfakh]

HAZ impact is about 120J at 0°C

No PWHT performed.

Regards