Weld to Weld Distance 2

[Sam Low]

Hi All,

Does anyone know why industry practice weld toe to weld toe distance have to be more than 50mm?
What are the concerns if the weld distance is lesser than 50mm?

Thanks in advance!

 

[LittleInch]

This has been debated since the concept of welding started.

50mm is a decent distance to prevent the Heat Affected Zone (HAZ) from each weld from overlapping.

A diagram and which code / standard or where you got the 50mm from would help.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[gtaw]

I hear the argument the space is needed to prevent the HAZ of one weld form impinging of the HAZ of the adjacent weld. If there was a problem with overlapping HAZs, why is it that were permit multipass welds? There is no provisions that prohibit multipass groove welds or multipass fillet welds. Each weld bead has a HAZ associated with it and they certainly overlap.

Is it an issue with regards to residual stresses? Once again, the magnitude of the residual stress is equal to the yield strength of the base metal. The base metal simply yields once the yield strength is attained.

You won't find much about it in most codes.

Best regards - Al

 

[LittleInch]

Multipass welds all occur a more or less the same time and hence the metal only gets heated up and cooled down the one time.

As you will find if you search these fora, most of these distances are simply "practices" or "recommendations" or are written into company or project specifications and are not code driven.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[gtaw]

Every weld bead deposited experiences a thermal cycle with a temperature increase to the melting temperature and then back down to the interpass temperature, which in the case of carbon steel or high strength low alloy steel would be well below the lower temperature of transformation. In the case of a multipass weld. the weld bead being deposited as well as the adjacent weld beads can also experience temperature excursions above the lower temperature of transformation and then cool to a temperature below the lower temperature of transformation.

In the case of pipe joints, it would not be typical for a welded joint to be completed using a single bead for all but thin walled pipe or tubing. So, the weld is going to undergo several thermal cycles. It would be no different for two separate welds, side by side, as it would be for a multiple pass weld. The thermal cycling would be very similar. The microstructure would also be very similar if the same preheat and interpass temperatures are similar.

Best regards - Al

 

[0707]

There is no specification on this matter IMO. If we have too close welds seams there is the possibility of HAZ sobreposition which affects the metalography of the two adjacent welds and its mechanical properties if a minimum distance can´t be respected.

The link below shows the comum practice used by the industry on this subject.

luis

https://pt.scribd.com/document/125978352/Minimum-Distance-Bw-Welds

 

[Sam Low]

Thanks LittleInch, gtaw and 0707 for the reply!

Seems like the main reason behind is to avoid overlapping of HAZ.
Appreciate it much!

 

[gtaw]

My point with regards to overlapping HAZs is that it is a nonissue for low carbon steels typical used for pipe. If you are welding a high strength low alloy steel that derives it's mechanical properties by controlled cooling rates or post weld heat treatment, one may need to give it more consideration. However, if you are welding ASTM A53, ASTM A105, or ASTM A106 it is pretty much a non-issue. Evry multiple bead groove weld has overlapping HAZs, yet no one gets their skivvies in a bunch up over that.

Best regards - Al

 

[Ron]

Agree with gtaw....mild steel, not an issue. Aluminum and certain steel alloys...think about it.