Welding steel fittings with different wall thicknesses
Welding steel fittings with different wall thicknesses
(OP)
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 .





RE: Welding steel fittings with different wall thicknesses
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
RE: Welding steel fittings with different wall thicknesses
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.
RE: Welding steel fittings with different wall thicknesses
RE: Welding steel fittings with different wall thicknesses
RE: Welding steel fittings with different wall thicknesses
BigInch
-born in the trenches.
http://virtualpipeline.spaces.msn.com
RE: Welding steel fittings with different wall thicknesses
RE: Welding steel fittings with different wall thicknesses
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.
RE: Welding steel fittings with different wall thicknesses
BigInch
-born in the trenches.
http://virtualpipeline.spaces.msn.com
RE: Welding steel fittings with different wall thicknesses
If this welded assembly is a part of any pressure conduit, the thickness difference cannot varry widely.
RE: Welding steel fittings with different wall thicknesses
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
RE: Welding steel fittings with different wall thicknesses
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.?)
RE: Welding steel fittings with different wall thicknesses