Elbow sizing for foam pigs 1

[ashwani25]

I have to pig a 24 inch crude line with a foam pig and I am unable to decide what size 90 deg elbow to use .

Should I choose 90 deg elbow of radius 1.5 D or 3D. I would also appreciate if you can refer me to a standard that has associated information about it as well.

Regards,
Ashwani Chandra

 

[zdas04]

You probably cannot even buy a 24 inch 1.5D 90. I know they are in the catalog, but I've never seen one in the wild. A foam pig will traverse a 1.5D elbow, but nothing else will (if you ever want to run a turbo pig, or a brush pig you are screwed). Generally if you are setting up a line that might need pigging, you forgo fittings and use hot bends with a bend diameter of at least 6D and 18 inch tangents so you can field weld with less drama.

David Simpson, PE
MuleShoe Engineering

Law is the common force organized to act as an obstacle of injustice Frédéric Bastiat

 

[ashwani25]

Thanks for your valuable input zdas. Can you also refer me to any industry standard that caters to the design of elbows or bends for pigging.

 

[IFRs]

ZDas has said it best.

Also, try using the internet for searching.
PigsUnlimited.com
The Art of Pigging
PipelineEngineering.com
TDwilliamnson.com

Contact suppliers to see what they carry.

Your situation ( current and future ) will determine the elbow radius you use. Standard long radius elbows have a 1.5D radius and are OK for only short, soft pigs. At

http://www.hackneyladish.com/DimensionData-pr1.aspx

are listed 3D elbows, but they may be rare. Induction bends are the way to go for larger radius bends and straight sections on both ends sure do make it easier in the field.

 

[ashwani25]

I am also interested in knowing what governs the decision making for selecting the radius of the fitting for pigging.

 

[IFRs]

It's basically what is needed to make it work. To select the radius I would look at operational issues for instance: the type of pig ( size, material, articulated, segmented, loose, tight, etc ), how many times it is needed to traverse the pipeline, how much pressure you have to push it, is it being pushed by liquid or gas, how far it has to go, how many elbows there are, how many potential exit points there are, how accessible the pipeline is ( for instance, 100% underground would tend to make one more conservative ), what the consequences are for it getting stuck etc. If it is just a simple, small foam pig in an above-ground line with 4 elbows, no un-barred tees, 1 mile long, being used once a year, separating liquid batches - go with 1.5D, make sure the pig manufacturer agrees with you and be done with it. I'd also consult with others in your company for their expertise - there is nothing like having done it before to help guide you in the future.

 

[ashwani25]

Thanks everyone for your valuable guidance . With all of you're support i was able to find the controlling factor for selecting pigs on long radius bends. There's an empirical rule that the ratio of the length of the pig to diameter of the pig should be less than or equal to 1.5 for long radius bends. if this condition is satisfied then the pig will be able to traverse through that bend radius. Using this analogy I checked TD Williamson's website for their line of pigging products and found the one which passes through long radius bends. Please check the attached pdf.


Once again thanks for showing me the right path.

Regards,
Ashwani Chandra

 

[LittleInch]

Ashwani,

Whilst you can find pigs that can traverse 1.5D bends, you seriously limit the supply, the risk of blockage or jamming is much higher and you effectively loose the ability to intelligently pig your line in the future. Don't forget that many pigs find it difficult to traverse elbows which are very close to each other or in different planes.

I've seen many

For anything that calls itself a pipeline (what code are you designing to?), as opposed to piping, and/or is buried at any point, you would be well advised to use at least 3D bends (not 1.5 D elbows) and preferably 5D or higher. You need to consider possible changes in operation , maintenance clearing and internal inspection over the next 25-30 years and how much difference these handful of bends (you give us no data on length and no of bends) are compared to the significant difficulties of pigging with 1.5D bends.

Quite frankly the cost of the bends as opposed to elbows is so low as to be insignificant when spread over the life of the pipeline, but would make it much easier to pig due to any currently unknown requirement in the future.

don't forget to use barred tees on branches > 0.3D of your main pipe.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[zdas04]

If you stick the TDW pig that the slick literature says will traverse a 1.5D bend, TDW will not pay to cut it out. The clearances on that thing are so tight that a handful of mill scale will stick it tight. I've been in situations where short-sighted engineers before me put things in the line that hampered future operations and it is far less fun than it sounds like it would be.

One example. A client purchased a field and found that the trunk lines were 8 inch Sched 5 and should be rated at 300 psig. My client was running the system at 560 psig (thank goodness for safety margins). The most cost effective fix was to pull a poly liner through the entire system. The liner could be pulled around a 3D bend, but not a 1.5D bend. Cutting out the 1.5D fittings and replacing them with 6D bends cost more than the liner.

David Simpson, PE
MuleShoe Engineering

Law is the common force organized to act as an obstacle of injustice Frédéric Bastiat

 

[BigInch]

Just goes to show you that pipelines should be made with 40D cold bends.

you must get smarter than the software you're using.

 

[zdas04]

I can't disagree, and I've seen that standard used in mainline jobs. I have a lot of trouble getting people to see the benefit in 6D bends, and my clients seem to think that they are excessive. I don't have that discussion with RTP so the problem seems to get worse as you go above 8-inch (I haven't run 6-inch or smaller steel for a decade, and I'm anxiously waiting for my first 8-inch job now that FlexSteel has an 8-inch product).

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

 

[ashwani25]

I see a lot of suggestions here made are as per empirical testing or based upon experience which would not help in documenting a design change. On my client side (Enbridge) the individuals need more than assurance that a long radius bend is enough for pigging.

During my research I came across many journals and articles which asserted more on using the same thumb rule ratio to be less than 1.5 for pig length to diameter. I double checked all the product line of TD williamson for scraper pigs dimension that most of their pigs had this minimum threshold for their corresponding line size.

I do realize that 1.5 D is a close dimension to work with assuming any hydrate formation that might cause the pig to stuck but this a close to 200 ft of line inside the facility being used for surge line , so only active during surge events.

TD williamson doesn't pay for cutting pipe surely but its surely provides technical support and we have requested that on our previous projects .

40 D cold bends are not at all possible as we have a limited real estate and also need to effectively design ur piping for allowing traffic patterns in and out of the station. For pipeline scope they would surely apply but not for onshore facilities.

The design for the 1.5 D is requested by my client as they don't want to overkill the design for a surge line despite our recommendation for a larger radius bends. So my job is to make sure I can envision things which would meet the client's demand without hampering operations , which would not have been possible if I didn't get to discuss with you guys.

 

[zdas04]

Not sure what you are looking for that you haven't gotten. The comments above represents at least 100 years of pipeline experience and probably a bit more. We've designed and operated a bunch of pipe. Just because you can't replicate that experience in 20 minutes on Google doesn't mean that you are safe in ignoring it (BTW, I've found TDW's recommendations to be pretty spotty, a few are as good of advice as you'll get anywhere, a few are reasonable techniques but far from best practices, many are just bad advice--it is hard for a novice to tell the difference). But the beauty of engineering is that there are a number of ways to solve any problem and you may find that by pandering to your client you have hit exactly the right mix of due diligence and blind sycophancy.

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

 

[ashwani25]

Its weird to know that more than a 100 year old practice doesn't have a standard written for correctly sizing the pigs. A google search is effective if one knows what exactly he is looking for, which proportionally reduces search time .

Shooting an arrow and painting a bullseye around it doesn't necessarily serve the purpose , facts need to be proven and with that minimum size control ratio of 1.5 for the pig the pieces started to fell in piece. The beauty lies in understanding the essence of an engineering principle and implementing it to respective conditions with its associated variable factors , a protocol that every novice should learn to follow and every experienced should try to remember.

 

[zdas04]

Ah yes, the old saying "hire teenagers while they still know everything" is still as true as it ever was.

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

 

[LittleInch]

ashwani,

Take the time and read back through your posts and the replies starting from the top and work out when it was exactly that you told us that you were looking at 60 odd metres of pipe inside a plant and not 60km of pipeline buried in the ground. You would have had a rather different response and I can't for the life of me understand why you want to pig this line.

BTW the 100 years was (at least) the combined experience years of the guys answering your questions, not 100 years of operation.

It may come as a surprise to you to discover that not everything in pipeline engineering is written down in a standard or code, but that's because there are simply too many variables to cover all the angles.

Interestingly enough I had a close look at the pigs listed in your previous attachment and the smallest ones are in fact > 1.5 L/D ratio. How this helps with deciding what size elbow to use is not clear, but at 24" you could use 1.5D, but as said before why you would ever contemplate this is much more difficult to understand....

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[ashwani25]

Please read Industrial Pigging Technology: Fundamentals, Components, Applications by Gerhard Hiltscher, Wolfgang Muhlthaler, Jorg Smits for better understanding and not correctly accomodating for the pig l/d ratio.