How much distance between bends so pig doesn't get stuck? 2

[LearnerN]

I'm looking a situation where I may need a vertical 15-deg bend and then a horizontal 16-deg bend fairly close together, and I would like to hear some recommendations/guidelines about what distance between the bends would be necessary so a tool or pig wouldn't get stuck in the line. Thank you!

(Or if you'd think it'd be better to have ONE horizontal vertically-rotated bend, please let me know any resources to determine how to calculate the bend that has both a horizontal and vertical angle.)

 

[C2it]

One for Big Inch really.

I know that two bends out of plane are worse than consecutive in-plane and some pigs do tighter bends, but the pig vendor ought to know the answer ?

 

[LearnerN]

Oh, and I forgot to clarify I'm talking about 6D bends. The only thing I'm uncertain about by just asking a pig vendor is not knowing if some other pig vendor would be used later down the road or whatever, but I guess I could take the pig vendor recommendation and make it more conservative than that.

 

[bimr]

Elbows and pipe bends installed in the pipeline should have a minimum radius of three times the main-line pipe diameter—3D bends. Intelligent pigs may require greater radius to diameter elbows and bends because of the longer length of the pigs.

While smart pigs may be capable of traversing tight bends, this may not be optimal for achieving the best possible inspection results especially for small diameter pipelines. It is recommended to use minimum bend radius 5D or even more 10D for smaller pipelines.

When operating at their minimum bend radius, smart pigs may require a distance of straight pipe equivalent to the tool length between adjacent pipeline bends. A rule of thumb is that there should be a length of straight pipe between bends of between 3D and 5D.

 

[zdas04]

Two important bits of information missing. What is your pipe size and what kind of pigs do you want to run?

Any fundamentally plastic pig(poly bullet pigs, foam pigs, turbo pigs, etc.) will traverse an infinite number of 6D radius bends connected back to back to back.

Steel mandrel pigs and smart pigs can be a bit of a problem. For mandrel pigs (where you can still get them, turbo pigs have pretty much replaced them) check with the manufacturer. Smart pig technology is changing rapidly. When I first heard of them they couldn't traverse a 30D radius bend. I was involved in running one a couple of years ago that could traverse a 90° fitting (3D). You need to talk to the vendor you are likely to use.

One mistake that a lot of people make with induction bends is not leaving enough room on the tangents. The first time I specified hot bends for a job I didn't specify tangent lengths and the shop politely cut the bends off at exactly 45° or 90°--the bend process will always flatten the pipe some and welding these out-of-round chunks to round pipe was a real pain. Now I specify 18" tangents and have never had a problem again. With 18" tangents on both your 15° and 16° bends would pretty much eliminate any unfortunate interactions between the bends.

The geometry of your two bends is not that difficult, but the technology is. Bending machines only operate in one plane and you can roll the bend in any direction, the more aggressive you get with that the more difficult fit up becomes.

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

 

[LearnerN]

10" liquids line. Pigs - anything they could possibly run in the next 40 years, anything from cleaning pigs to smart pigs.

 

[zdas04]

It has been 20 years since I last saw a 10-inch steel mandrel pig. There are configurations of turbo pigs that do everything we used to do with mandrel pigs (brushes, scrappers, etc.). That makes life a lot easier. I would also say that it is very unlikely that you would have a problem with your two bends with today's smart pigs.

If you are still nervous, there is no reason you can't have your pipe fabricated with 10D radius bends instead of 6D (which is really the minimum bend radius for hot bends, not the only bend radius).

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

 

[BigInch]

If an intelligent pig can go around a 5Dx90[°], how could it not go round a 5Dx180. So no space is required between 90s, less between 45s, however as zdas notes, be sure to leave the shorter of either a 2D long tangent, or 18" (+/- 500mm) on each side of a bend, so the pipe can be held at the ends during the bending process, or cut, beveled and welded up with room for a cutout or two if necessary during installation.