Thickness calculation for high temp service, Div. 1 vs B31.3 1

[jtseng123]

All,
Div 1, UG-27 does not have weld joint strength reduction factor (W) to calculate thickness while B31.3, para 304.1.2 does for high temperature service.
For stainless steel at 1450 degF, the reduction factor 'W' is 0.545, which means B31.3 will have twice of the thickness than Div 1.

1). I am making my 48" OD x 150' long pipe (304H SS at 1450 degF) to be designed and fabricated per Div. 1, not B31.3. Doing that, the thickness is 1" per Div 1 instead of 2" per B31.3, that will save a lot of money and improve schedule (not just saving the material and welding, but also support system and foundation design). Any problem ?

2). In the above real case, the weld metal is normally 308H. If I am forced to go by B31.3, can I use 16-8-2 weld metal, which has better creep rupture property than 308H weld metal and 304H base metal, and take W=1 instead of 0.545 so I can still get 1" thick from B31.3 ? Has anyone have the experience ?

Jeff

 

[TGS4]

What's your design pressure?

 

[SnTMan]

Is the applicable Code really your choice?

 

[jtseng123]

The design pressure is 60 psig. B31.3 for piping and and Div 1 or 2 for vessels will be the codes we use.

This is for a real petrochemical project that produces gasoline from crude oil. Everything I deal daily is all real project, from design, procurement, fabrication to construction. I have been doing pressure vessels and piping stress analysis since 1990 in a big engineering company in Houston. Normally I do not have problems with codes since we have to comply. Once a while, there will be a hipcup, just like PWHT I posted in another thread and this one.

Jeff

 

[SnTMan]

"1). I am making my 48" OD x 150' long pipe (304H SS at 1450 degF) to be designed and fabricated per Div. 1, not B31.3. ... Any problem ?"

"The design pressure is 60 psig. B31.3 for piping..."

Uh, yeah, problem

 

[doct9960]

And what is the design temperature of your metal? On your other post you mentioned refractory lining.

If you are designing a pipe line, stick with the B31.3 code.

 

[jtseng123]

It is for SS at 1450 metal temp/60 psig.

 

[TGS4]

What are the allowables for your specific material specification/grade of material in both VIII-1 and B31.3? You mentioned 304H, but not the material spec. There's over 10 different material specs with grade 304H, many of which have different high-temp allowables.

 

[jtseng123]

the duct will be rolled from plate by SA240-304H with allowable stress 1800psi at 1450F. Any 304H grade will have that allowable stress, more or less.
There is no need for anyone to run the thickness and pont out my thickness calc is wrong or material is not suitable, which is irrelevant to my (2) questions. The twice of the thickness from B31.3 is the true fact, that costs a lot. I have been thinking Div 1 is more stringent than B31.3, but not true for PWHT and high temp service.

 

[DSB123]

It is about time ASME got their act together and rationalised the codes. Problem is too many individual commitees. Look at B31.1 and B31.3 for instance one has weld strength reduction factors whilst the does not. Its a joke.

 

[moltenmetal]

There is nothing to my knowledge wrong with designating and designing and fabricating a 48" section of pipe as a vessel per Section VIII Div 1 rather than a pipe per B31.3. There are relief and other requirements that Section VIII will require of you, but the savings of half the wall thickness will probably pay for those handily.

 

[TGS4]

DBS123 - excellent idea. Please submit your offer to volunteer to do this work to the B31 Committee secretary.

 

[TGS4]

moltenmetal - I would generally agree with you. However, depending on the jurisdiction, there may be some repair/re-rate issues down the road. Some jurisdictions handle piping very differently from pressure vessels. So, if it in the future you need to do a repair to the "duct", you would fall under completely different rules if it were piping vs. vessel.

ASK your client which they would prefer it to be. Sure, the captial cost will factor into the equation, but it's not the sole consideration.

 

[doct9960]

Don't forget to add manways per UG-46. And some ladders and platforms if the manways are not accessible from grade.

 

[jtseng123]

Thanks TGS4. I am making the decison for our client. No U or R stamp is required if it is Div. 1. Repair is not an issue since we have experience of it regardless what code.
I opt for Div 1 not only saving the cost, but it has more piping flexibilty by less thickness that will ease the loading at the ends connecting to vessel and rotating equipment.
Since there is no wled strength reduction in Div. 1, my real concern is the girth seam that will see the longitudinal bending stress from sustained loads (pressure+weight). Do I need to consider weld strength reduction for the girth seam when I run the pipe stress flexibility analysis(which means allowable longitudinal stress will be redcued by almost 50% in my case)? Can I use 16-8-2 weld metal (costs more) and ignore the weld strength reduction so I can easlily qualify the pipe stress analysis ?
Anyone has done so ?

 

[rhg]

This is not a technical problem, it´s a commercial one.

Regards

rhg