Temper beading and hot tapping 1

[kevlar49]

Does anyone temper bead carbon steel split sleeve hot taps? I am thinking of doing this to minimize risk of hydrogen embrittlement of sour water lines. Preheat and bakeout not feasible so HAZ softening seems to be the only choice.

Initial thoughts were to add a low heat input butter layer all the way around and then weld build up over that or make incremental butter layers followed immediately with tempering layers. Any comments?

 

[metengr]

What is the hot tap sleeve thickness, and the pipe material?

 

[kevlar49]

This is for a hypothetical situation, but applications I am starting to get questions on are usually hot tapping done for lines <10" NPS and up to 500# flange rating. Sorry, don't have more specific information than that. Pipe material is usually A106 Gr. B, but can't be sure of the vintage of some others. Plant was built in 1968. I'm concerned with places where CE>0.35.

thanks.

 

[metengr]

kevlar49;
I have seen information regarding a temper bead welding approach to welding split sleeve hot tap connections on existing piping systems.

Using the temper bead approach to tie in the circumferential fillet welds to the existing piping system for 10" and under NPS and the split sleeve full penetration welds is an excellent approach. Regarding HAC susceptibility from welding, I would strongly recommend using low hydrogen weld electrodes, specifically the H4 designator for SMAW. The issue of CE has more to do with susceptibility to HAC. Despite the possibility of higher CE’s in certain applications related to higher carbon versus low alloy steel, what you do have working for you is thinner wall pipe material and the increased heat input with proper execution of the temper bead approach to temper the base metal HAZ and subsequent weld passes. I don’t see any problems if your CE is 0.5 or less.

One last item, I would use a mock-up to simulate one of your hot tap set-ups to assure the welders can follow a temper bead requirement as part of the welding instruction. The deposition of the butter layer and remaining on top of the butter layer with sequential weld passes (without touching either parent material) and achieving proper weld bead overlap are critical for successful temper bead welding.

 

[kevlar49]

Thanks metengr,

You said that you've seen temper beading for split sleeves before. Are there any good references for the welding sequence applied (standards, handbooks, etc).

thanks again. Very good advice.

 

[kevlar49]

An issue came up with temper beading large diameter pipe. What is a good way to do that? Most welders tend to traverse the circumference once for the butter pass and then place the next passes. However, I was thinking that they should put subsequent passes on before finishing the entire circumference. Any comments?

 

[metengr]

"Most welders tend to traverse the circumference once for the butter pass and then place the next passes."

Yes, this is absolutely correct. Remember, the objective of temper bead is to temper the previous weld passes and to also temper the base metal HAZ from the butter layer.

Sequentially, the butter layer should be deposited first circumferentially with a tight bead overlap (50%). Once the entire butter layer is deposited, the second and remaining weld passes must be placed while remaining on top of the butter layer. After about the 3rd pass, you can switch to a convention method of weld deposition because the remainder of the tempering occurs from heat input beyond the 3rd layer. Do not forget that you need to apply additional weld reinforcement to temper the last pass. This weld reinforcement layer needs to be removed after temper bead welding to reach the last pass that was subjected to tempering.