Tube-to-tubesheet weldjoints or not...

[WeldingPartner]

Hi All,

Reviewing welding procedures, I suddenly realized not to have a solid answer regarding the following question:

What is the crucial difference between a "normal" (fillet pipe to plate)weldjoint and a "tube-to-tubesheet" weldjoint requiring a special mock-up test.

Looking forward to your opinions.

Best regards,
Weldingpartner.

 

[metengr]

What is the crucial difference between a "normal" (fillet pipe to plate)weldjoint and a "tube-to-tubesheet" weldjoint requiring a special mock-up test.

The difference is what the Code of construction requires for a tube-to-tubesheet weld joint. See ASME B&PV Code, Section VIII, Div 1, and what the owners specification requires.

 

[SnTMan]

WeldingPartner, more specifically, see Appendix A and UW-20.

Regards,

Mike

 

[chicopee]

I think what you want to know is that tubes welded to tubesheets are called seal welds which you would see on many firetube boilers and watertube boiler drum tubesheets which during a retubing job tubesheet holes were damaged could not maintain a tightness around the tube sheet holes.
Seal welds are of light layer deposit with no real strength.
Now having said that, you will see watertube boiler drum tubesheets with full or partial penetration welds on tube ends but these are more strength welds than seal welds.
Get a NBIC manual and you will get additional info.

 

[WeldingPartner]

Thanks for your responses sofar.
Unfortunately not useful yet.
I'll try to be more specific:
We have a Tubesheet with a tube bundle, to be welded. No problem. However, one (1) of the tubes has a complete different diam + wallth., and outside the tube pattern. The weld configuration is identical to those of the tube bundle.
So, although this special tube has the same function as the other tubes, the weld-to-the-tubesheet is to my opinion not to be qualified as per ASME IX, QW-193, but just like a standard pipe-to-plate filletweld.

What is decisive in determining the type of weld - plus the type of PQR - here?

The manufactures proposes to qualify using a standard buttweld PQR...

Thanks for your opinions in advance,


Rgrds.
WeldingPartner

 

[metengr]

However, one (1) of the tubes has a complete different diam + wallth., and outside the tube pattern. The weld configuration is identical to those of the tube bundle.
So, although this special tube has the same function as the other tubes, the weld-to-the-tubesheet is to my opinion not to be qualified as per ASME IX, QW-193, but just like a standard pipe-to-plate filletweld.

Well, thanks for the added information, that sure helps us.

Are you referring to a tubesheet stay??????

 

[WeldingPartner]

Hello Metengr.

No, I'm not talking about a Tubesheet stay.

Rgrds,

WeldingPartner

 

[metengr]

WeldingPartner;
If this tube is not typical of the existing tubes in the tubesheet and provides the same function, you cannot simply use an alternative approach for the weld. If this is a tube to tubesheet weld configuration and performs the same function as the other tubes, it must be treated as such from a weld procedure qualification. This is how I see it, if I was the customer.

 

[unclesyd]

Is the larger tube a hot or cold bypass maybe with a damper.
We have several single pass bundles that have this feature. As the bypass is normally much larger than the remaining tubes we treat this as a separate entity. Again normally the bypass can't be roll so the tube to tubesheet weld has to be a strength weld of a totally different configuration. We usually just let a shop welder make this weld. The weld configuration is usually to bevel the hole to a depth equal to the twice the tube wall and add a fillet weld on top of that.

 

[metengr]

I agree with unclesyd that if this larger diameter tube is for venting purposes only and is not rolled into the tubesheet, this would be a partial penetration groove/fillet weld design, and this would be qualified using a standard groove weld procedure.

However, you need to confirm this because from reading your original post, you stated this large tube was also rolled in the tubesheet, so it must be treated as a rolled and seal welded tube, like the others.

 

[WeldingPartner]

Thanks a lot,

Reading your answers helped me on a workable track.
So, it is really great to know a forum like this.

However, don't hesitate to post a clear definition (with reference to the source) regarding the specific difference between tube-to-tubesheet weld and plate-to-tube weld, if it exists...

Best Regards,

WeldPartner.

 

[Cheops]

You will find useful information in Section IX paragraphs QW-202.6 and QW-193. The extent of qualification tests depends upon the criticality of the application. For critical applications (high pressure, highly corrosive, lethal or other dangerous fluids, high loads on the joint, etc... , it is good practice to use QW-193).

Tube-to-tubesheet is very different from pipe to plate weld. In general, this is where failures occur in a heat exchanger. Tubes are usually relatively thin, which means that the weld size is also limited. When large loads from differential thermal expansion of the tubes / tubesheets are present, combined with vibration due to fluid flowing in and across the tubes, corrosion, erosion, etc..., these joints become the weakest point in the system