Minimum thicknesses between Elbows and Straight Pipe 3

[SaCaZu]

Greetings,

...I'd like to know if exists some criterion that let me say that the allowable minimum thickness in an elbow must be greater than allowable minimum thickness in a straight pipe for its replacement due to that the elbows are points with erosion rate higher than straight pipes.

...It's to say, I've been reading and analysing this situation since the point of view of security, where any system based on high pressure and temperature requires to define critical leves of replacement.

...Thank you in advance for your opinions

 

[vesselfab]

i don't think the codes really address the amount of extra material for erosion & corrosion. The amount of metal added is up to a qualified engineer with experience in the process being used and corrosion caused by it and life expectancy and the inspection procedures and records of the user.

 

[jte]

No Code requirements here that I know of. The only things specified are the wall thickness at the welding ends, and the geometry of the ends. What goes on between point A and B is left to the imagination of the fabricator. In theory, and yes, I know this is ridiculous, a fabricator could build a 12" Sch 80 90 deg LR ell by having the end be Sch 80 and at the correct locations, make a short radius 45 to a straight run, then another short 45 to link up at the other end in the right location. The wall thickness of the straight run could be Sch 40, as long as it passes a burst test. Actually, the fabricator could burst test a 10" and 16" ell of similar construction and not actually test a 12" version. It would look funny and not many folks would buy 'em... but they could in theory meet B16.11 as far as I know.

So... No, there is no code requirement for an elbow to be thicker than the pipe. If it is thicker due to the increased stresses at various locations, then realize that it is thicker due to mechanical stress reasons and not as additional corrosion allowance. Thus, even an elbow which is thicker at some part than the pipe to which it mates up, it does not inherently have more corrosion allowance.

jt

 

[pennpiper]

jte,
You wrote: "The wall thickness of the straight run could be Sch 40, as long as it passes a burst test."

Am I miss reading your post?
There is NO "straight run" on a LR 90 degree ELL or on a 45 degree ELL or on a SR 90 degree ELL.

The geometry of a standard 90 degree elbow is the same as if you took an automobile tire and cut it into 4 equal quadrants. There is no straight run!

Where did you get this idea.

 

[jte]

penn-

I believe I did mention "...I know this is ridiculous..." but my point is: What code says that the elbow should look like a quarter tire (as you put it)? There is guidance which states that it should start and end at the quadrants, but not what goes on in between, as far as I know. If you find some section which does, let me know.

jt

 

[MJCronin]

All..

Doesn't API 570 address this issue,,?

I believe that a minimum thickness is calculated (based on pipe diameter, material,etc) and the entire system, incuding elbows and tees) is checked for this minimum.

-MJC