Welding steel fittings with different wall thicknesses

[testingpump]

Is there are any limitations or restrictions for the welding of steel fittings / pipes with different wall thicknesses , or what is the minimum percent of wall thickness for the thinner wall thickness piece comparing to the thicker wall thickness piece .

 

[BigInch]

Yes, as I recall, maximum is about 3/16" difference, but see your code.

quoting from the NavFac,

The procedures for making transition welds between different materials or between plates or pipes of different wall thicknesses shall be qualified. ASME B31.1, ASME B31.3, ASME B31.4, ASME B31.5, ASME B31.8
requirements for branch connections may be used in lieu of detailed designs.

BigInch-born in the trenches.

http://virtualpipeline.spaces.msn.com

 

[pennpiper]

Yes, you can weld one piping object to another piping object that have different wall thicknesses. Piping objects include pipe, fittings and flanges.

When you do this you should have a very good reason for doing it and (if the difference in wall thickness exceeds the code allowance) you must taper bore the thicker wall to match the thinner wall inside diameter.

 

[pipe15]

ASME B16.25 details buttwelding prep for exactly this situation. It provides guidance, but might not yield the best configuration if NDE is required.

 

[odem]

API 1104 (Welding) allows 3/16" without transitioning or taper boring.

 

[BigInch]

For those that don't know, API 1104 is for pipeline welding.

BigInch-born in the trenches.

http://virtualpipeline.spaces.msn.com

 

[11echo]

...AND if you do have to weld different wall thicknesses where wall thickness is over 0.187 you'll need to back taper the bores at a 4 to 1 taper min.

 

[rconner]

Whatever the applicable code is in the area/application, it should of course be complied with in this regard. However, aside from that and from a purely physical/philosophical standpoint it is obvious that it is physically possible to weld two pipe or fittings of whatever wall thicknesses together (of course as long as there is suitable radial interference in the dimensions of joining ends!) What one gets however when one does this is are inevitable "stress concentrations". There is a similar parallel for argument in a common application when e.g. a thin steel plate or gusset is welded to a much thicker plate, or e.g. when a very small diameter (and naturally much thinner) outlet or nozzle is welded to the side of a larger, thicker pipe.
The magnitude of stress concentration (or localized stress multiplier) is in a sense dependent on the off-set, the type/design of joining weld, and also I guess on the nature/direction of load application to the connection. In the extremes of provision for this in e.g. the thick tube, special products field (where cost is not necessarily as determining a factor and high loads/reliability/fatigue resistance etc. are a common object), I have seen some folks apply a slight excess/overlay of weld for some length each way in the thickness transitioning joint, and then in effect grind or machine smooth a “radius” in the transitioning weld area.
Stress concentration factors are available in mechanical engineering and other references for radii and other common fabrication transitions, to allow detailed stress analyses of the effects of the design chosen (and of course the smoother the transition and the larger the radius, the less the stress concentration or multiplier). I suspect where this is covered in code the code fathers or mothers have considered this effect in some fashion.
All that being said, in applications where there are not very high axial, bending, nor cyclical loads etc., and very high joining efficiencies are not necessarily required, there are weld joining means that it would apepar readily allow different thicknesses of pipes or fittings to be weld joined together with common fillet welds (particularly e.g. when there is a common outside diameters). Examples of this are “lap-welded slip”, “butt-strap”, and also various fillet welded rubber gasket joints such as shown (along with single and double butt-welded) in AWWA Manual M11 for steel water pipe, as well as perhaps some exterior socket weld type stuff for smaller pipes in other applications.

 

[BigInch]

I'd say its also for the difficulty of making a good weld when one piece is sinking off most all of the heat to one side and the resultant differential cooling and probability of cracking the completed weld, overcapped or not.

BigInch-born in the trenches.

http://virtualpipeline.spaces.msn.com

 

[piping4hydrocarbon]

There is no thickness ratio limitation in joining dissimilar thicknesses as long as 1:3 tapper is maintained and welding ends are per ASME B16.25.
If this welded assembly is a part of any pressure conduit, the thickness difference cannot varry widely.

 

[NozzleTwister]

One word of caution if matching liner higher strength pipe to thicker lower strength fittings.

If you taper bore the lower strength material to match the higher strength wall thickness, the lower strength component may no longer be adequate for the design pressure at temperature.

Something to think about....


NozzleTwister
Houston, Texas

 

[rconner]

piping4hydrocarbon,
I think I understand the intent/context of your statement “If this welded assembly is a part of any pressure conduit, the thickness difference cannot vary widely…” however, I think there have actually been some types of composite pipes (though I suspect not used much in the hydrocarbon field) claimed suitable for pressure service such as prestressed and pre-tensioned or bar-wrapped concrete pipes that have intentionally started out with a welded fabrication wherein a very thin (I think intended to be basically a water-proofing) steel membrane has been routinely welded to a steel end-ring that is generally much thicker (in just a very few inch axial length). [The “pressure”carrying capability of such pipe, at least from the hoop perspective, is basically intended to be provided by quite highly stressed/at least initially high strength small wires or tendons that are subsequently wrapped outside this fabrication.]
Of course also, I believe many other folks are promoting that various quite thick flanges and hubs etc. be also quite routinely welded e.g. to quite thin steel and particularly stainless steel ducting and even pressure pipes etc. (due to weight/material cost etc.?)

 

[X60]

As I understand it simply, according to ANSI tolerances it is + 12.5& - 10% or vice versa, safety speaking. For instance let's say you can weld 20" x 0.500" pipe to a 20" x 0.563" fitting without any problem. This is assuming I understand your question correctly?