design of weldolets

[frankytea]

I'm in the business of quality checking high pressure vessels and there is a frequent use of weldolets (depending on project pressures range from 300# to 2500#) for connecting Sch 40 branch pipes to similar run pipes. I've got MSS-SP-97:2006 on my desk and I am a little confused as it is not very clear (at least to me).

Firstly it doesn't discuss the dimensions of the cross section of normal butt-weld weldolets so I am not sure whether the diameters on these weldolets are correct. I frequently find stuff on tinternet how can I do not know what diameter the weldolet should be at.

Secondly it refers to 'reducing' and 'full' weldolets. I understand reducing but full... is that interchangeable to 'through'?

I've looked at bonnyforge and wfi and according to the illustrations its a bit of both.

That aside...

As the pipes that come on my desk have many branches (for sensor inputs) using reducing tees would be impractically as that would mean that a lot of reducing tees on the single pipe strip. However the tipping point between using weldolets for reinforcement or just welding directly on the run pipe is very unclear to me. Any pointers?

 

[rustbuster]

Generally the WOL's are sixzed to the mating nominal pipe size.
Reucing WOL is size on another size eg. 1" on 10"
Foll WOL is size on size eg 4" on 4"

WOL's are more cost effective than butt welded tees and a much stronger design than stub on / stub in connections.

Hope that helps

 

[rneill]

The only industry standard for WOL's is MSS SP-97 (which you have) but unfortunately, it does not fully dimension the product. Consequently, there is some variation between manufacturers as to the specific dimensions used.

When ordering a WOL you would want to specify the run and branch sizes and wall thicknesses to ensure the WOL provided for adequate reinforcement on the run pipe and suitable dimensions for welding to the branch pipe.

Note: WOLs are used on piping but not vessels (as they are to an MSS standard and not an ASME Standard). They aren't recognized for vessel construction.

API RP14E Table 4.1 provides guidance with regards to when a WOL vs. a tee or reducing tee should be used. In general, WOL's are reserved for small branches and would not be used as the branch size approaches the run pipe size. Also, they are not preferred in service subject to fatigue failures as they have much higher stress intensification factors than do tees or reducing tees. Fabricated stub-in connections (pipe into pipe) while permitted by Code are rarely used for most piping systems although at very large sizes, you may still see them.

 

[frankytea]

Thanks rustbuster for clearing up the confusing about full and reducing. And thanks to rneill for giving me a document to go to - I will have a closer look on monday. Great help!

Quote rneill, "Note: WOLs are used on piping but not vessels (as they are to an MSS standard and not an ASME Standard). They aren't recognized for vessel construction."

That is my fault for calling the multiphase flow meters that I'm checking as vessels and not pipes (if pipes is even the right terminology).

I am particularly interested in the accurate design of WOL because their design has a knock on effect on what size hole I need to drill in the run pipe and thus how much spacing adjacent branch connections can have (from centre to centre) which has far and wide design repercussions.

Somewhat related - if a WOL is welded onto the run pipe and then welded onto the branch pipe (or vice-a-versa) isn't that considered as an overlapping of heat affecting zones (HAZ)? I want to weld the WOL onto the branch connection, radiograph it, and then weld the WOL-branch combo onto the run pipe. Practical in any way? Thanks!

 

[pennpiper]

frankytea
You wrote:
"I'm in the business of quality checking high pressure vessels ........ I've got MSS-SP-97:2006 on my desk and I am a little confused as it is not very clear (at least to me)."

I suggest that you go visit one or more of the "Weld-O-Let" manufacturers and learn about how they are designed and manufactured. The alternate is to call them and ask them to send you their technical data on WOL's

As for the spacing of WOL branches, they can be spaced to allow real or assumed flanges on the branch lines to be side by side plus one inch.

As for which joint should be made first, the WOL to run pipe or the WOL to the branch pipe. It does not make any difference.

 

[frankytea]

Thanks pennpiper on suggesting to get in the mix with WOL manufacturers - it will certainly be interesting.

That aside what is your opinion of the remark about overlapping heat affected zones? At work I'm pushing the design to incorporate a minimum distance between weld lines such that HAZs don't overlap but my argument is shot down when I am using WOL. Any light?

 

[pennpiper]

It is fairly common for Engineering companies to establish their own guidelines for minimum spacing of pipe welds. Many use three times the wall thickness of the run pipe as the minimum. Others use one pipe diameter or some dimension (3"or 4")

When less than the minimum the exception is that you can always put it in the heat treat oven and Normalize the piece.

What is your material?

 

[rneill]

Take a look at Pipe Fabrication Institute ES-7 "Minimum Length and Spacing for Welded Nozzles".