D/t ratio of 107

[jonjose123]

Hi All,

We have a pipeline of 42" with wall thickness of 9.5 mm which accounts for D/t ratio of 107. Stress Point of view this satisfies. However, code (DEP) specifies the D/t ratio to be less than 96.

Is there any particular reason other than handling problems.

The pipe is buried and is of length 2 km.

 

[BigInch]

Out of roundness and local buckling.
Do you need an written approved variance from the DEP?

"He's declaring war on the planet itself."- Vicente Fox

 

[LittleInch]

Agree,

When you work out the OOR and ovality spec of the pipe at that size and wt, the pipe can be within spec, but literally parts of it won't touch the next pipe to weld it.

Finding someone to make it could also be interesting...

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

 

[KevinNZ]

When D/t gets too 100 the piping deign codes have limits e.g B31.3 304.3.1 (b) (1). Piping stress programmes also warn they are not accurate.

We have built many KM of large pipe, DN1200 9.52mm, above ground. Design around supports needs care, We treat these location like pressure vessels and design the shoes with pressure vessel rules and FEA.

Field fit is fun! Just the sun warming the top of the pipe bows the pipe and puts the weld alignment way off.

 

[LittleInch]

Makes you wonder if the saving on metal makes up for all that special treatment and extra construction work.

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

 

[BigInch]

Does it? Economy varies between projects. This can be a significant variable. If your project has high welding and labor costs, but relatively low steel and transport cost, your budget might be blown already.

If the savings would be greater, the D/t ratio limit would be higher. IE there's a reason why it is where it is today.

"He's declaring war on the planet itself."- Vicente Fox

 

[jonjose123]

Thanks Biginch, Littleinch and Kevin for the reply.

So The main concern is only regarding the OOR and Ovality and handling issues right. Hope this can be solved at site.

 

[LittleInch]

"Hope"???

If you're the designer you're supposed to take all this into account and balance the competing factors to arrive at an acceptable design which satisfies the technical requirements at the lowest OVERALL cost. This includes therefore any additional costs in the field caused by using pipe which results in delays, poor welding, rejection of welds, buckling a couple of pipes maybe.

That's what engineering design is - "Hope" doesn't come into it.

To simply say "Hope this can be solved at site" is IMHO, abdicating your responsibility as a designer.

I "hope" you turn up on site and listen to the stream of "comments" you get, some of which may not be as "constructive" as you would like.

/rant over

LI

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

 

[BigInch]

Will the real Alfred E. Newman please stand up.
So after I told you, you're still not worried about local buckling.
You still don't know how little an imperfection of out of roundness or point bearing it would take to buckle it.

"He's declaring war on the planet itself."- Vicente Fox

 

[DSB123]

BI,
Looks like Price Charles as a kid with them Wing nuts

 

[BigInch]

Ya. I see some resemblence.
Maybe he's not so internationally known.
Alfred is the "mascot" of Mad Magazine.
He appears there with the phrase that he made famous.

"He's declaring war on the planet itself."- Vicente Fox

 

[auzie5]

Our buried pipeline specs limit D/t to less than 70 to avoid issues related to use of high D/t Ratio (e.g. flattening, ovality, buckling, increased risk of denting). Use of higher D/t ratio can be approved on a case-by-case basis but for our pipelines, it is rare to come up with a compelling reason to use line pipe with higher D/t ratios.

I’m curious if others here have company specs that restrict the use of high D/t line pipe for buried pipeline projects and if so, what that limit is. It would also be interesting to hear of the highest D/t line pipe people have used for onshore buried pipeline projects. We did a NPS 36 x 9.5mmWT (D/t = ~96) Gr. 290 sales oil line a few years back…only designed to operate at 1,200 kPa. We had an aweful time with ovality which was only discovered after backfill. It was around then we revised our specs to limit use of high D/t line pipe.

 

[BigInch]

You should have run a gaging pig after installation to pick up excessive ovalizations.

All B31.4 designs are limited to 100.

"He's declaring war on the planet itself."- Vicente Fox

 

[auzie5]

Yes we run aluminum gauge plate pig runs after pipeline installation on all pipelines...sized to ~95% ID...same as everybody else...That's how we discovered the ovality issues...

For bigger pipeline projects we also run an ILI caliper tool with nitrogen after backfill...it's better at finding instances of other distortions that a gauge plate will pass over. And the caliper tool gives an accurate location of any features.

 

[BigInch]

Even better!

"He's declaring war on the planet itself."- Vicente Fox