When can you use class 1 division 1 design factor in B31.8 1

[LittleInch]

So I'm old enough to remember when the class 1, division 1 came into being and as far as I can remember, it was specifically listed as being for places which are basically "uninhabited". The implication being NO dwellings in your 1 mile long zone.

However the versions of B31.8 going back to at least 2014 are now very vague and appear to offer no guidance on when you can use class 1 division 1 - see the wording below.

So is there a code case on this? Or any further guidance?

Has anyone managed to use a DF of 0.8 under ASME B31.8?

For info this is the current wording in ASME B 31.8 2018

(a) Location Class 1. A Location Class 1 is any 1-mi (1.6-
km) section that has 10 or fewer buildings intended for
human occupancy. A Location Class 1 is intended to reflect
areas such as wasteland, deserts, mountains, grazing land,
farmland, and sparsely populated areas.
(1) Class 1, Division 1. This Division is a Location Class
1 where the design factor of the pipe is greater than 0.72
but equal to or less than 0.80. (See Table 841.1.6-2 for
exceptions to design factor.)
(2) Class 1, Division 2. This Division is a Location Class
1 where the design factor of the pipe is equal to or less than
0.72. (See Table 841.1.6-2 for exceptions to design factor.)

The table listed is just the table showing different design factors for crossings etc

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[danschwind]

LI,

I have no practical experience with this, but upon reading the paragraphs related to division 1 or division 2, I think this decision is up to the designer - it seems Division 2 requires a lower test pressure than Division 1. This at least on the 2007 version:

"(1) Class 1, Division 1. This Division is a Location
Class 1 where the design factor of the pipe is greater
than 0.72 but equal to or less than 0.80 and has been
hydrostatically tested to 1.25 times the maximum
operating pressure. (See Table 841.114B for exceptions
to design factor.)

(2) Class 1, Division 2. This Division is a Location
Class 1 where the design factor of the pipe is equal to
or less than 0.72 and has been tested to 1.1 times the
maximum operating pressure. (See Table 841.114B for
exceptions to design factor.)"

But as I said, I have absolutely no practical experience in this and my opinion may be totally wrong. I'm interested in seeing other's opinions. Maybe there is a table somewhere in the 2018 stating the test pressure?

Daniel
Rio de Janeiro - Brazil

 

[LittleInch]

Yes, the earlier versions basically implied the pipeline needed to be nearly flat because test pressure was basically at SMYS (1/0.8) leaving no room for pressure at a lower elevation so you would be over SMYS as soon as the elevation changed from your high point. Thus the flat empty plains of texas come to mind but even that description has vanished from the code.

Maybe people realised that there was an issue over test pressure and that's why no one has built any but I'd like to know.

Thanks for input.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[danschwind]

LI,

Pardon my utter ignorance in the subject, but I haven't understood what you said. Is the test pressure directly related to the SMYS? I thought upon reading the paragraph that it would be related to operating pressure only. I'm away from the standard right now to check and educate myself on this.

Daniel
Rio de Janeiro - Brazil

 

[LittleInch]

In 31.8 there is a relationship between test pressure and MAOP (=TP/1.25) which is the inverse of the test pressure (1.25 x MOP)

So on the basis that you want your MAOP to be equal to the design pressure (otherwise why are bothering to use a 0.8 DF) then with a DF of 0.8, assuming no other factors, your DP, MAOP and MOP are all 80% of the SMYS. So your test pressure (0.8 x 1.25 = 1) is then at or very close to the SMYS of the pipe (depending on your choice of wall thickness).

So therefore any elevation difference between the highest point ( which is where the test pressure applies) and the lowest point will therefore raise the stress in the lowest point above SYMS.

Now in reality you might get say 5% above SMYS before you really start yielding, but that equates normally to <100m elevation difference in your test section.

So whilst 0.8 DF sounds really good to reduce wall thickness, you run into practical issues when trying to test it.

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Also: If you get a response it's polite to respond to it.

 

[danschwind]

Ah, I get it now! Thanks for the explanation!

Daniel
Rio de Janeiro - Brazil

 

[1503-44]

I think 0.80 was used for a lot of the Bakken Gas Pipeline design, but that would technically fall under CFR 49, Part 192.


“What I told you was true ... from a certain point of view.” - Obi-Wan Kenobi, "Return of the Jedi"

 

[1503-44]

BTW I think, if not mistaken, that I saw that in a pipeline industry article written about an explosion that occurred on that line shortly after it was placed in service. To verify, you may be able to find an associated accident report on that incident in PHMSA files.

“What I told you was true ... from a certain point of view.” - Obi-Wan Kenobi, "Return of the Jedi"

 

[LittleInch]

Thanks - I'll investigate some more. Still trying to find any guidance issued on when this is applicable...

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[1503-44]

Guidance specific to B31.8? Otherwise I believe that Canadians and Australians have used a lot of 0.8 design permitted by their codes. In the US, 0.80 was being used on occasion in remote areas (no houses anywhere to be seen) uder a "special permission" provision (during a testing phase) before it was actually published in the CFR. Not sure how it is goinglately, ever since those campers were blown up (in Arizona?) while they were camping on one of those "extremely remote" RoWs.

“What I told you was true ... from a certain point of view.” - Obi-Wan Kenobi, "Return of the Jedi"

 

[LittleInch]

ASME 31.8, but also any other codes would be useful.

My issue is that the original guidance in /B 31.8 specifically stated "no habitation" as far as I recall, but this wording has vanished from the code for 10 years or more. So what happens now?.

The ISO code is a bit more helpful

"The hoop stress factor may be increased to 0,83 for pipelines conveying category C and D
fluids at locations subject to infrequent human activity and without permanent human habitation
(such as deserts and tundra regions)"

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[1503-44]

CFR reference Title 49 Part 192 ?
Page 11 for pp 111/112
page 90 for pp 620 Use of DF 0.80

https://www.phmsa.dot.gov/sites/phmsa.dot.gov/files/docs/49_192_highlight_8_15.pdf

“What I told you was true ... from a certain point of view.” - Obi-Wan Kenobi, "Return of the Jedi"

 

[LittleInch]

I've not been able to find out much more.

The best I can find is the description in the ISO code for their top class of locations i.e.

Locations subject to infrequent human activity with no permanent human habitation. Location
class 1 is intended to reflect inaccessible areas such as deserts and tundra regions.

As the wt is subject to under tolerance unlike B31.8, this is equivalent to 0.8. Also there is dispensation for lowering the test pressure to 1.2 X MAOP so that the highest point is close to SMYS.

So the same limitations start to apply about a limited amount of elevation difference allowed before you start to hit yield at the lowest point.

Given the apparent complete lack of guidance in B 31.8 I would use this definition as the start point for any consideration.

Thoughts anyone?

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Also: If you get a response it's polite to respond to it.

 

[1503-44]

That definition works for me.

OK. So how bad do you want to use 0.80? If you can save a couple of tons of money using a thinner wall, it might even pay for a repair or two, or 10, if the test goes wrong. You might evaluate using a test pressure slightly higher than yield. We used to do tests to 1.05 yield. They liked the idea of redistributing stresses more evenly in the plastic range. The company was even doing that offshore, until I got there. They were newbies offshore. I convinced them that they might not want to do that, given the much greater cost of repairs offshore if something went pop. You'll want to keep your good eye on the pressure gage vs. volume of water in the test segment graph when you get up over yield stress pressure. If the curve breaks sharply to the right, stop the pump.

“What I told you was true ... from a certain point of view.” - Obi-Wan Kenobi, "Return of the Jedi"