Using B31.3 Chapter IX for low pressure pipe

[ARenko]

We have a company standard that requires the use of B31.3 for wall thickness design. Some pipe manufactured before this standard does not meet the design criteria of Chapter 2 - it's 3000 psi pipe made from L80 tubing (API 5CT). It is a significant amount that management does not want to take out of service. This pipe has high yield stress - 80 ksi (tensile is 95 ksi). I believe using Chapter IX for wall thickness will allow for higher allowable stress (still need a closer look).

If I understand K300(a) correctly we are not bound by the >2500# definition for "High Pressure Fluid Service," correct? Using Chapter IX may allow a lesser wall thickness than by Chapter 2, however, we would also have to comply with all requirements of Chapter IX (of which I haven't done a thorough review to see what those requirements would be). Am I correct? Are there any major issues we should be aware of if we take this approach?

 

[BigInch]

Why not just sit down and read the code.
You must use the listed allowable stress for the material.
You must design for the maximum pressure you will have in your system.
If you are designing pipe, you use the provisions for determining wall thickness given in B31.3
Now please calmly take a seat and enjoy some inspirational reading.

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https://www.dropbox.com/s/r9mygqm70sm4hx5/OMG something else.png?dl=0

 

[ARenko]

I do plan to read more as I have time - was looking for some confirmation on my understanding of the scope. The material is not listed.

 

[BigInch]

Ya. Not a good idea to use high strength materials in B31.3. You'll probably have to derate it to a default material's stress allowable.


[img =

https://www.dropbox.com/s/r9mygqm70sm4hx5/OMG something else.png?dl=0

 

[if7005]

First, make sure you allowable stress whether designed for elevated temperature. Check most identical material to Table A-1, then see rating from B16.5 whether >2500.

 

[LittleInch]

It's a novel idea alright, but I personally think it's stretching the boundaries of the intent of that section i.e.

"High pressure is considered herein
to be pressure in excess of that allowed by the
ASME B16.5 Class 2500 rating for the specified design
temperature and material group."

I realise there is a "however" after it, but it would be pretty clear to me that the basic intent is exactly what it says.

As ever the ultimate issue is risk and responsibility. You take the responsibility and the risk is that in the event your pipe goes bang, then someone finds out you designed a #600 system using rules designed for > #2500 then it would be open season from the lawyers.....

If I re-read this is the issue that pipe already installed to one code is now being subjected to a revised design based on a different code? Are they mad? This is like scrapping pipe just because a new version of the code comes out - not done.

I just had a quick glance at Chapter 9 - seems like the allowable S increase for similar pipe (X80), but you get no overpressure allowance and I'm sure there are other oddities which make it different from "standard" B 31.3 design.

My motto: Learn something new every day

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

 

[XL83NL]

Apart from the useful replies youve already had (by BI and LI), assiginign high pressure fluid service also has certain client involvement. Typically, major oil&gas companies assign sucgh Fluid services to a piping system, as they now the intention of the service. If your client does this (or indictaes it is okay that guys go ahead with this pipe as a 'Chap IX pipe'), and you're using B31.3, you still need to comply with Chap IX. Then you're stuck.

The code does not prohibit you from using other equations than the basic wall thickness eq in the base code (3a). Refer to para 300(c)(3). Hence there may be means to use other formula's that yield higher allowable pressures or lower wall thicknesses, provided you comply with the requirements of the Code.
What you therefore might do, is e.g. review Becht's book on the Guide to Process Piping. In there youll find other approaches to wall thickness determiation (I think its in the part where he discusses the Lame equation derivation). You also could use the wall thickness equations from ASME VIII-1 app. 1.
However, if you deviate from the base Code requirements, I would advice to document this carefully in your engineering design, so your client can approve and accept this (see 300(c)(3)), and that for future checks, youll always be able to track down what and how did it.

 

[ARenko]

If I re-read this is the issue that pipe already installed to one code is now being subjected to a revised design based on a different code? Are they mad? This is like scrapping pipe just because a new version of the code comes out - not done.

There is no design code applied to the pipe - someone used a completely arbitrary method of determining wall thickness. Basically taking 70% of nominal wall and checking that the pipe doesn't yield. Safety factors ranged from just over 1 to almost 2 (when compared to yield). When I found out I suggested they comply with B31.3, apply those wall thicknesses to existing pipe, remove any from service that don't have enough wall, and follow B31.3 for any new pipe. Unfortunately they continued to buy the same pipe although they did apply the min wall thicknesses I calculated. But as I warned, this would result in zero to short life on most of the pipe (i.e. new pipe could be below or very near min wall before ever going into service). They have 95% kick out rate after 1 year and don't want to accept it since they've been using the lower wall thickness numbers for 20+ years. This is temporary pipework in O&G applications. Anyway, looking more in depth at Chapter IX I can see other areas the pipe won't comply.

 

[LittleInch]

Astonishing. How has anyone got away with this for that long?

I don't believe in the word "temporary" when if comes to any O + G application. I've seen "temporary" pipework that is still there 20 years later and I think it breeds a certain lack of rigour in design, construction and operation which is really quite dangerous.

I wish you lick in your endeavours and you're almost certainly going about it the right way, but would be interesting to know why you chose B 31.3 and not either a pipeline code or any other design code.

My motto: Learn something new every day

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

 

[ARenko]

It's temporary in the sense that it's rigged up and down frequently - it's used to connect equipment to the wellhead or other equipment for well service and drilling applications. B31.3 is the code most clients and class societies require and the code that the major mfrs of this type of pipe design to.

 

[LittleInch]

All the more reason why you need a fair bit of "fat" in your design to allow for constant make and re-make and the rather brutal world that sort of pipe will live in.

My motto: Learn something new every day

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

 

[BigInch]

In the States, even permanent onshore gas well piping isn't necessarily governed by any pipe design code, or regulation. Maybe OSHA has a few work safety paragraphs, but not pertaining to wall thickness selection.

I started introducing "code designs" in south Texas unregulated gathering systems in the 80's and got a lot of resistance from the independent producer I worked for then. Most pipe, valves and fittings were never identifiable by spec, never mind hydrotest any piece of pipe, no corrosion control program, no welder qualifications, WWII submarine engines for compressor drivers, no mapping records of pipe, tie-in locations, used glycol dehys and air coolers, quick inspection and gas um up. I guess down on the border, and probably a lot of other remote and unregulated locations, it's still pretty much a cowboy's paradise. "Code" was how the Russians talked to the CIA.