Aerial Cooler Header Box in Lethal Service

[thermmech]

RE: Lethal Service

I went through the threads and also examined ASME VIII-1 UW-2(1)(c) - and I am still not sure whether aerial cooler header box joints can be made as Cat C (corner joints) with 100%UT or they have to be as per Figure UW-13.3.

 

[gr2vessels]

Without details of the design pressure and temperature, I would think that you'd design the cooler to Division 2, specifying Lethal service in the UDS. That is, use Fig. AD-701.3 for those corner joints.
However, the fig. UW-13.2 is for the header boxes designed to Div. 1.

gr2vessels

 

[thermmech]

DPs range from 75 to 500 psig, while none of the DTs exceeds 400°F.

Process fluids contain H2S. We would like to have a design to ASME VIII-1.

Is it OK to assume that joints for rectangular boxes (I'm talking about Div 1 design) can be 100% UT'd in lieu of 100% RT? Will that satisfy the requirements of UW-2?

 

[gr2vessels]

It looks like the 100% RT cannot be substituted with UT, in lethal service, unless it is a full fusion welding without filler metal (not your case anyway). I'll get a good advice from a "wise man" and come back to you shortly.
By the way, is it wet sour service or is lethal service?
Cheers,
gr2vessels

 

[thermmech]

Well, that's exactly what is being debated right now. The practice in a lot of Sulphur Removal Plants is not to designate any piece of equipment to be in "Lethal" service, but rather in "Sour" service. Although the NDE requirements are almost identical (Sour vs. Lethal), Sour service is easier to comply with (ignoring the material chemistry requriements) as there are no special construction details.

My understanding is that Para UW-2(a)(1)(b): "All joints of Categories B and C shall be Type No. (1) or No. (2) of Table UW-12." effectivelly prohibits type "C" weld joints(standard corner weld joint) on header boxes. In other words, hub type joints are mandatory as shown in FIG. UW-13.3.

I would appreciate any other comments that you might have.
Regards,

 

[doct9960]

s27289,

See Code Case 2235 (Use of Ultrasonic Examination in Lieu of Radiography) if this is applicable to your case.

http://www.sonotronndt.com/pdf\ASME.pdf

Check with your AI and jurisdiction if this is acceptable.

 

[thermmech]

doct9960;

Thanks for the Code Case. The only outstanding issue is than whether the tubesheets and plugsheets have to have a hub (i.e. for joints to be butt welded) as per Fig UW-13.3.

I will definitely check with the AI as well.

Regards,

 

[doct9960]

s27289,

My understanding of UW-2(a)(1)(b) is the same as yours. Category C joints for box headers in lethal service should only be butt weld joints (Type 1 or 2). Therefore, corner weld joints (Type 7) are not allowed for box headers in lethal service.

If your company is the User, somebody in your organization must verify if the exchanger is really in "lethal service". As you may have already read in UW-2(a), "...it shall be the responsibility of the of the user and/or his designated agent to determine if it is lethal. If determined as lethal, the user and/or his designated agent shall so advise the designer and/or Manufacturer."

 

[thermmech]

We're working on the decision... I have read the other threads and it seems that there is no concensus on whether H2S service is Lethal or just Sour.

Thank you!

 

[gr2vessels]

s27289,
I have checked out other countries classification and the conclusion is identical;- the wet sour service is classified very harmful liquid to human, but not lethal.
I believe that you should look for the hazard classification of the H2S (in Solution and Liquefied) around the world, to build your position.
Cheers,
gr2vessels

 

[thermmech]

gr2vessels,
Thank you veru much!

 

[gr2vessels]

Good luck,

Cheers.
gr2vessels

 

[doct9960]

s27289,

For Alberta,Canada, the following are some interesting info/links about H2S:

http://www.capp.ca/raw.asp?x=1&dt=PDF&dn=61443

http://www.hre.gov.ab.ca/documents/WHS/WHS-PUB_ch029.pdf

H2S concentrations above 300 ppm is lethal.

When I was in college, we had a field trip to a refinery. While touring the plant, I sensed the smell of rotten egg. I asked our guide what the smell was and he said it was H2S coming from their Sulfur Recovery Unit. The guide said that he preferred the smell of rotten egg than not sensing (smelling) H2S. He said that if you are exposed to H2S and there is no smell, you could become unconscious or just drop dead. That was my first enlightenment about H2S.

 

[thermmech]

doct9960,
Thank you for the info!