Welding steels of largely different yield strengths

[EngDM]

Hey all,

Steel supplier is insisting on using A53 Gr. B, with a yield strength of 240MPa, but the baseplate we are welding to has a yield strength of 300MPa. In the weld tables of HSC CSA16-14 (Blue book) there is no listing for 240MPa yield strength base material, and it appears that it wouldn't use matching electrodes anyways.

What is the correct procedure when welding materials that don't share a matching electrode as far as sizing the weld. Is it as simple as using the smaller electrode capacity to be conservative, and then the W59 qualified welder will worry about how it is welded?

I saw this thread

https://www.eng-tips.com/viewthread.cfm?qid=327466

which seems to use E49xx (Canadian equivalent to E70xx) even though the matching electrodes conditions table doesn't list A53.

 

[desertfox]

Hi EngDM

Have a look at this site it might help

https://www.millerwelds.com/resourc...ctors-for-selecting-the-right-stick-electrode

“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein

 

[CANPRO]

I'm assuming your typical notes call for E70xx electrodes and I wouldn't change that. From a design perspective, you'll be more likely to have the base metal govern the weld design. I see you're using CSA S16-14, the 2019 code is the most recent. Check the weld tables in Part 3 (table 3-25) and compare the values in the 2014 version to the 2019 version if you can. In the 2014 edition, the weld capacities level off at about 45deg where is in the 2019 edition the values continue to increase all the way up to 90deg. That is because the base metal check was removed in 2019. There was some debate in my office if that was appropriate or not. In your case, with the lower base metal value, you really should be checking the base metal capacity.

In terms of welding the two grades together, it is not an issue. A53 Gr. B is common for handrails and is commonly welded to 300W plate. Be aware that those pipe sections often don't meet the requirements of the building code if being used as a hand/guard rail. If they're asking for the substitution take a close look at the potential change in yield and cross-section values.

 

[EngDM]

If they're asking for the substitution take a close look at the potential change in yield and cross-section values.

I've checked the cross section, I've had to go with an XS pipe, which I wouldn't be surprised they come back and ask for STD, in which case the pipe won't work and I'll recommend 300W HSS. As far as checking the base metal, if you have a round section would your tension area be half the circle, so find stress with the S of that shape WRT the centroid?

Who know's, this company has sent me mill reports for A500 that were WAY higher than the typical yield, maybe they will do the same for this.

 

[dik]

I determine the weld strength based on the object being welded, the base material and the weld material, and use the lowest value of the three.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[desertfox]

You should match the electrode properties to the lower strength steel but also check the design of your joint from a point of service conditions ie external load etc. With welded joints that fail it’s not the the weld that fails, the failure is often the base metal in the HAZ (heat affected zone)which will be governed by the tensile strength of the weaker material.

https://www.thefabricator.com/thefa...elding/welding-metals-of-dissimilar-strengths

“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein

 

[EngDM]

I determine the weld strength based on the object being welded, the base material and the weld material, and use the lowest value of the three.

Am I understanding correctly that checking the base material would consist of making sure σ = My/I < ΦFy (For all around welds, otherwise it would be fusion face)? You could substitute y/I for 1/S. In the case where the section class is plastic, would it be appropriate to use Z? If I don't use Z in pipes case, the stress calculation fails using elastic section modulus even though moment passes.

 

[WinelandV]

No, that's not what the base material check is.

In AISC's SCM, there's a check for the minimum thickness of base material to fully develop the weld:

In imperial units, tmin = 3.09 * D / Fu (for 70ksi electrodes), where D is the required number of sixteenths of an inch in weld size (i.e. D = 4 means 1/4" fillet leg).
[Equation 9-2 - for fillet welds only on one side of an element]

Please note that is a "v" (as in Violin) not a "y".

 

[dik]

I use the minimum weld value for all materials. In addition I calculate the minimum material thickness as well as the minimum weld size based on material thickness. I guess I could use the plastic modulus, but I don't. The reason the code used the plastic modulus for capacity (for elastic design) is that 'plastic' conforming sections are a little more robust and allow greater deformation for redistribution. I'm a big advocate for plastic 'plastic' design. I only use the elastic section properties. Connections are not the area where I want to save money.

In keeping with Packer's recommendations for HSS connections, I do not adjust the strength based on the direction of load.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[EngDM]

I use the minimum weld value for all materials. In addition I calculate the minimum material thickness as well as the minimum weld size based on material thickness.

Do you know of a Canadian reference book that goes a bit more in depth on baseplate design and checking welds/base metal etc? Is the base metal check checking the fusion face?

All I'm trying to work through is a guardrail post connection to a baseplate.

 

[CANPRO]

EngDM - you the reference you need to check the weld; S16-14. As noted above, S16-19 is the most recent and there was a change in how the base metal check is handled. I suggest reading through S16-14 and S16-19, both code and commentary, to get a better understanding of this concept. See excerpt from the 2019 commentary which discusses the base metal check.

 

[dik]

No I don't. I check with references for 'new' material... I generally don't use references for day-to-day design... just codes. I think the CISC used to have a companion design guide to go with CSA S16. I have a couple of references... Jeff Packers book is one I often look at as well as the AISC and CIDECT design guides. Most of my material is just from common use.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik