ASME B31.4 - Mitered Bends out of spec

[EloyRD]

Dear comunity:

I'm dealing with the task of justifying the use of mitered bends that were field constructed without consideration for what is established in ASME B31.4-2009 404.2.4.

The pipeline starts with a manifold connected to 4 Vertical Centrifugal Pumps each one rated to 585m3/h @ TDH 326m.

The pipeline goes through the following route:
- Start at km 0+000 @3692 masl
- Downhill to km 0+192 @3672 masl (slope of -10.4%)
- Uphill to km 1+071 @3952 masl (slope of 31.9%)
- Uphill to km 2+250 @3990 masl (slope of 3.2%)

The pipes' material is Carbon Steel ASTM-A53 and its size is 24in.

The pipeline was constructed with mitered bends even where hoop stress of more than 20% was present, and operated with one pump for three months. In a few months the system will have to work non-stop with the four pumps for four months and the client expresses concern for having those mitered bends and request them to be replaced or justified.

I haven't found a reference or methodology to justify those mitered bends and I'll appreciate any hint to a resource.

Kind regards.

Eloy RD

 

[racookpe1978]

You can't tell (or even guess) until you know the actual angle of each miter bend.

Assume there were 120 miters, but all but 2x were less than 10 degrees. Just those 2x "might" be bad.

Also, what were the interior angles (nbr of sections) of the miters that are more than 10 degrees?

 

[LittleInch]

To be honest, I hope you don't find a justification as mitre bends are just a recipe for disaster, hence why you very rarely see them and they are wisely prohibited for pipelines with a hoop stress above 20%. 31.4 is quite clear on this for good reasons.

I would recomend spending your time working out how to replace the bends rather than trying to justify something which has a high risk of failure. If you really want to continue then you're probably down the route of FEA analyis and stress analysis of the pieline to prove that it doesn't work.

Sorry, but that's my opinion.

My motto: Learn something new every day

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

 

[EloyRD]

@racookpe1978 I've been asking for the angles of each junction but there hasn't been an answer yet from the field technical office. I'll check to see if we're really in a big problem of 20 joints or we are talking of only 3 or 4.

@LittleInch I've most definitely taken your advice and we're making a plan for the replacement of all the non conforming bends. Some people suggested trying to justify the mitered bends as per B31.3 but that showed us how weak the bends were, so the senior design engineers decided that it wasn't worth risking engineering reputation to justify bad construction.

We only have the doubt now if the mitered bends should have been detailed in the pipeline layout or if it was correct to let that be detailed by the field technical office.

Thanks for the comments.

Kind regards.

Eloy RD

 

[LittleInch]

That's a good decision.

Your bends should be detailed on the as built alignment sheets.

My motto: Learn something new every day

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

 

[MJCronin]

Does anyone else see this as a Management responsibility issue...??? or is it just me..

"the use of mitered bends that were field constructed without consideration for what is established in ASME B31.4-2009 404.2.4."

Does everyone understand that when project Management is irresponsible, hires field incompetents and lets the construction forces do whatever they decide, it is MANAGEMENT who deserves the blame !!

Why is the normal course of business to allow the field to do something...then dump ALL responsibility on engineering ?

Is this what today's crop of MBAs learn in business school ?

Heroic efforts by the engineer to take responsibility and try to justify faulty designs by the clowns in the field ALWAYS ends in disaster......... and usually includes the loss of a job for the engineer.

Does anyone ever wonder why only new engineers post these types of questions ?
Its because the last engineer in that job working on a similar field screw-up got fired because he came up with the wrong answer !

Dump the MBA who allowed these changes without approval..... establish a system of Field change orders and save money in the long run.....!