I have recently been asked to update a standard drawing design which includes a 1" nozzle projecting from a larger diameter elbow. But the problem in terms of structural strength, welding practicality etc is whether to make it a 'set on' or 'set in' nozzle. Has anybody else out there looked into the pros and cons of each possibility? Any advice, links, references etc would be really appreciated.
Cheers.
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If inside of wall is accessible a set in nozzle is highly preferred, as a full penetration of good quality is easier to obtain. Also, if a full penetration is not a must, the set in nozzle may be welded with two fillet welds. However, when vessel wall thickness becomes large (over 3/4"?) and is much larger than that of the nozzle, a sit on nozzle may become more practicable. Weld thickness becomes smaller and this occasionally may allow to avoid a PWHT.
ASME B31.3 Figure 328.5.4D shows both - either method is acceptable (be sure to verify if add'l reinforcing is required.)
My preference is the "set on" (a.k.a. saddle on) method - because it's self-supporting during fit-up. You don't have to worry about the nozzle or branch dropping through the hole before the welder gets a tack in place.
Also, the "o-let" family of branch connection fittings are intended to be "set on" the pipe.
The weld-in (contour)type of fitting has many theortical advantages. The weld-in includes a generous "forged-in crotch radius" that results in enhanced structural advantages. It can be seen in B31.3, Appendix "D" that the SIF is significantly less for the weld-in fitting and that bodes well for fatigue life. Also note that "the o-let" family of fittings includes both the weld-on (wled-o-let) and the weld-in (sweep-o-let).
BUT, it is easier to fabricate branch connections that employ the weld-on type fittings.
I agree with John. They make an elbolet which were used very successfully by my company for many years. The were required in the process piping specs for large diameter S/S pipe and heavy carbon steel jacketed piping. Water piping was the one exception where either method of attachment was allowed. We never had a in service problem with elbolets and I don’t believed we ever had one to drop out on analysis. If it hadn’t been for inspections most our set-ins or set-ons would have been left outs. If I was forced to decide whether to use a set-on or set- in, I would try hard to get a set-in nozzle. The only in service problems I’ve seen were with the set-on nozzles. I might be biased because during most of my years service the head piping designers have always liked set-ins or let-ins.
Never understood why process engineers always want a thermoweld in the worst case elbow.
Which ever type you decide to use put it in right and treat it right. Watch the chainfalls.
Always thought that both set-in and set-on nozzles were technically acceptable the decision to use one or the other being a question of which is the cheapest weld to make.
Athomas236, Not being critical I think I would have used the words "most economical for this situation" instead of cheapest. This word scares me when it comes to welding. I've seen too many cheap welds, in fact yesterday. The ones I saw yesterday, Ray Charles could have done better. The word cheapest is usually picked up by upper management and the battle is on. Over the years, when forced to accept welding contractors our group deemed marginal in qualifications the cost of rework was squared not doubled.
Hi Thanks very much for all the various perspectives. It thus appears that while both methods of nozzle attachment are technically sound, the criteria for choosing between the two options thus becomes a practicality and cost issue.
Having attended many conceptual pre-project meetings where you have everyone present and ready to pounce,I learned that a word sometimes carried more weight than 1" bolt. Though most of these meetings are as exciting as watching a Lava Lamp there is always a pickup and play on words. I had a magazine article that had 100 words to never use and 100 words to use. I remember that “cheap” was one to never use because you had no out. Where as if you use the something like “most economical” you have some hedge room. There might have been some accountants from "MBOT’s" company watching.
I didn’t take my own advice “don’t lead with your lips”
1) for piping the "set on "type of the branch connection is generally the rule.Use therefore a self reinforced type of branch i.e. a sockolet for a 1" branch, with a contour matching the elbow OD; 2) hope you weld the branch on the neutral axes and not on the extra or intrados of the elbow; 3)for a pressure vessel use "set in " nozzles;strength wise the minimum nozzle size should be 2".
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"Set in" nozzles versus "Set on" nozzles - pros &cons?