Is a welded tubesheet joint a category B or C?

[jeevesme]

Is a welded tubesheet joint considered a Category B or Category C joint? And if an efficiency of 1.0 is wanted, does it have to be RT'd (or UT'd)? Here is a pic of what i am talking about . . . .

Also, if i specify a Joint Efficiency of .85, is it governed by the lowest joint effiency of the entire vessel? For example, I have a heat exchanger with welded tubesheets and welded channels with mutiple nozzles. The nozzles have a Category D, Type 3 Joint with no RT, does that make the vessel a Joint Efficiency of .60?

 

[SnTMan]

jeevesme, I believe a tube-ts weld joint has no category assigned. UW-3 states that not all weld joints are categorized.

Second, joint efficiency is applied only to butt-joints. Corner joints are assigned E = 1 when needed. See Table UW-12 Type (7).

Third, joint efficiency is used for design of a single component only. E for any component does not depend on the E of any other. See UW-12, second sentence.

Your nozzles likely are corner joints, no E needed.

Recommend further reading, including Appendix L.

Regards,

Mike

 

[jeevesme]

I think we are going to have some of the joints UT'd or RT'd for peace of mind . . . . but it boggles my mind that an entire heat exchanger can be built without having any RT done and still have a Joint Efficiency of 1 per code.

 

[weldstan]

jeevesme,
Your joint shown is Catagory C. One can make tubesheet to shell welds as catagory B as well.

 

[jeevesme]

Thanks for quick replies guys. Much appreciated.

 

[jeevesme]

If Joint Efficiency only applies to butt welds, why does the code address weld types 4,5,& 6? Also, I just found this article...... Look at question 4....Wouldnt this indicate that nozzles are taken into consideration when it comes to joint efficiency?

 

[GenB]

Joint is 100%. You need a separate procedure to weld tube to t.s.

 

[SnTMan]

I might have more properly said "Second, joint efficiency based on RT is applied only to butt-joints."

Regards,

Mike

 

[muld0020]

Your configuration is showing Cat C Type 7 joints. RT/UT is not applicable for these joints since there is no applicable efficiency. They need to meet UW13 for corner joints, and you can meet your efficiency of 1 requirement on the vessel. There are other examples of this case in Code interpretations such as seamless pipe between fixed tubesheets in a heat exchanger.

If you require RT then go to a Butt Weld configuration with a hub machined into your tubesheet, but there are additional criteria such as App 20 if you have a plate or additional tensile testing to UW-13(f) for forgings.

 

[EdStainless]

The picture is not of a tube-to-tubbesheet weld.
I am not sure what component it is.
As has been stated, T-to-TS welds are a class of their own. Seal weld only, seal with filler, strength welds, again with and without filler, flush, recessed, back face........There are many variations and each has its own needs.

= = = = = = = = = = = = = = = = = = = =
Plymouth Tube

 

[SnTMan]

Yeah, never did understand the sketch.

 

[jeevesme]

Sorry about the bad sketch . . . here is what i am talking about . . .

 

[SnTMan]

jeevesme, as to tube-ts joint, I still do not assign it a category. It is a Type 7 corner joint, no RT needed, E = 1, if needed.

Your nozzles and cylinder-tubesheet joints appear to be corner joints, no RT needed, E = 1 if needed.

If cylinders are butt-welded, both Cat A and Cat B joints, E will be assigned based on RT selected. E will only be used for design of the cylinders, and perhaps some other calculations such as in Part UHX, but will affect only the cylinders. Cat A joints likely will govern.

Your vessel has no "overall" joint efficiency.

Regards,

Mike