Pipeline Class Locations

[gazepdapi]

This is just a general question but where do the requirements for the class location originate from? So for example, a class 1 is intended for 10 or fewer buildings or dwellings. My question is why is it 10 and not 11 or no? Who made the decision that it was 10 for class 1 and 46 for class 2, etc?

 

[BigInch]

US Congress? CFR Title 49 Part 192

I really don't know. Good question.

 

[gazepdapi]

Yeah I know the code it comes from but what made them determine the # of buildings? What's it based on? I think you know what I'm asking.

 

[LittleInch]

It is a crude form of QRA and when allied to the thickness of steel equates to a similar level of risk for each of the locations. How they decided the numbers you'll need to go back to the 70's at least.

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

 

[zdas04]

BigInch,
You got that one backwards. Part 192 took the table from ASME B31.8 table 841.114B. Project B31 was started by an organization that became the American National Standards Institute) in 1926 at the request of ASME (this is from the B31.8 Forward). The first edition was published in 1935 with a fairly stable version being published in 1942. The pipe thickness calculations changed in 1947, and then the whole thing was reorganized into the sections we know and love today (as best I can tell, that was when Location Class was introduced, but I'm not certain). The first edition of B31.8 was in 1952 built almost entirely from the 1951 Section 2, 6, and 7. 49 CFR 192 became law in 1970.

The table in ASME B31.8 came from the fertile minds of the committee and the companies they represent(ed). They wanted Class 1 to represent "sparse population" and being mostly engineers felt obligated to stick a number to "sparse" and it became "less than 10". As it was related to me many years ago there was zero science or statistical risk assessment that went into that number. They just wanted "sparse". Same way with the upper limit of Class 2 being 46.

David Simpson, PE
MuleShoe Engineering

In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual. Galileo Galilei, Italian Physicist

 

[gazepdapi]

That's where the conversation at work breaks down too...."you'll have to look back awhile ago to figure it out". Thanks anyways guys

 

[LittleInch]

see the attached which appears to be a good reference study. Appears to come from surveys in the 1950's showing how many pipelines would be affected if they reduced the max SMYS from 0.72 to lower than that (5%) and then worked out number of buildings. I like the fact that the original 1/2 mile corridor was because that was the size of the aerial photo, but then was reduced to 1/4 mile in total later on.

There are a couple of references which don't come up in a search but it seems authentic.

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

 

[gazepdapi]

That was a good reference littleinch...do you have direct link to that article?

Looks like it gets as close as we can to the answer. Looks obvious to me it was just a number out of thin air that the committee picked

 

[LittleInch]

It was a PG&E document, but I had to get if off google cache. I think it is some sort of deposition, not an article per se, but the info is there at the start of the document.

I don't think they plucked it from thin air exactly, but made a reasoned study - there is mention that some consulting engineers were involved - to turn what was agreed to be "typical" low density - 1 - low to medium -2 - and high density from the aerial photos into numbers people could use. There also seems to have been some investigation into how this would affect design in terms of percent of a route that would be affected.



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

 

[BigInch]

Similar text and a complete document, by Penspen Engineers with a discussion of DF across several codes

http://www.penspen.com/wp-content/uploads/2014/09/high-design-factor.pdf