Welding a member on top of an existing weld

[pinaki_stahlbau]

Hello,

I am working on a construction project in Europe and the fabricators have proposed a T joint, where in the 3rd member sits on an existing groove joint. The idea is that the groove joint will be first formed and inspected thoroughly for any defects and then the thinner plate comes and sits on the existing weld metal.

My questions is if this is valid and if any special checks need to be carried out. If such a thing is indeed okayed by any norm or book, could you direct me to one.

Thanks

 

[TugboatEng]

Do you plan to grind or machine the weld flat prior to fitting the T? That seems like a lot of labor.

 

[pinaki_stahlbau]

Do you plan to grind or machine the weld flat prior to fitting the T? That seems like a lot of labor.

Well yeah. The surface will be prepared and leveled before the 20 mm plate is installed.

 

[kingnero]

Make sure you use wire suitable for multi layer welds. Some wire/flux combinations don't have the ductility for something like this.
Can't say for sure without more details, but this shouldn't be a problem. In construction, you'll be using run of the mill materials, and 10 mm is nothing compared to some other things.

 

[MintJulep]

98% of fabrication shops would just shotgun a filet weld symbol on anything that looks like a T.

Having a properly called out CJP weld suggests that whoever put it there knows what they're doing. Have a discussion with them.

There's a big difference in mass. Pre-heat will be important.

 

[pinaki_stahlbau]

Thanks for your replies.

These guys are actually pretty good. They for sure know things from a fabrication standpoint, but we are the structural consultants and need to approve this before it goes up. The CJP weld is more for Low cycle fatigue issues. However from structural design standpoint, I have two concerns which makes me hesitant.

1. The 20 mm plate is sitting directly on the PJP and transfers load to the weld metal. The PJP weld is designed for the usual forces (bending, shear and axial in the horizontal plate), but how do you even check for the local stresses induced by this 20 mm plate CJPed on top of this. None of the codes talk about such situations.

2. Moreover, it's not even sitting on a virgin base metal. Once welded you cannot even see, if the heating actually worsened things below in the underlying weld metal.

 

[gtaw]

The residual stress in the longitudinal direction will be about the same as the yield strength of the weld/base metal.

Is this added detail being added to an existing structure or is this a "new" fabrication?

Question: How can the added member, the 20 mm plate, be subject to fatigue, but not the member it is welded to? Assuming both the heavier member welded using partial joint a penetration groove weld and the 20 m plate are subject to fatigue, is the PJP groove weld appropriate? Just asking for a friend.

 

[pinaki_stahlbau]

T

The residual stress in the longitudinal direction will be about the same as the yield strength of the weld/base metal.

Is this added detail being added to an existing structure or is this a "new" fabrication?

Question: How can the added member, the 20 mm plate, be subject to fatigue, but not the member it is welded to? Assuming both the heavier member welded using partial joint a penetration groove weld and the 20 m plate are subject to fatigue, is the PJP groove weld appropriate? Just asking for a friend.

No everything's new. Not on any existing structure.

That's a good question, about the fatigue. However, the fatigue calculations are done by some third party wind experts and their structural team. Both of them are obviously subjected to fatigue and my guess is that with the forces in there and a fillet weld being in the lowest detail category for fatigue, they decided to go CJP instead of a very big fillet weld. However for the horizontal member, the welds were probably sufficient.