Minimum practical wall thickness for pipelines

[sfol552004]

Is there a minimum practical wall thickness to stay above for about 8 thru about 24 inch pipelines?
I know the D/t < 100 rule, but I've spoken to pipeliners that seem to feel .25 inch is the smallest they will use. We recently ran an 8 inch that was .219 without any trouble. Just curious what the sentiments are.

 

[MechEng2005]

Pipe must be able to support the weight of the pipe and fluid inside, for one thing.

 

[BigInch]

Nothing wrong with less wt given that it is mechanically sufficient, but you should be prepared to pay attention to potential corrosion issues during its lifetime. Corrosion is the #1 cause of "pipeline incidents". Otherwise try to stay with the DWT100 rule.

Independent events are seldomly independent.

 

[SectionIX]

With the beief that you are transporting gas, oil, etc, Barlows will determine the minimum required thickness.

 

[SNORGY]

In Canada, the CSA Z245.1 Standard used to include a tabulation of available standard wall thicknesses, of which the following were called up as "special thin wall":

8" from 4.0 mm down to 3.2 mm
10" from 5.2 mm down to 4.0 mm
12" from 5.6 mm down to 4.4 mm
14" from 7.1 mm down to 4.8 mm
16" from 7.1 mm down to 4.8 mm
18" from 7.1 mm down to 4.8 mm
20" from 7.1 mm down to 4.8 mm
22" from 7.1 mm down to 5.6 mm
24" from 7.1 mm down to 5.6 mm

The above reflects regular line pipe that is outside of pump / compressor stations, uncased road crossings and uncased rail crossings. If one was inside those limits, the (ultimately interpreted) "thin wall thresholds" were:

8" from 4.0 mm downward
10" from 5.2 mm downward
12" from 5.6 mm downward
to 24", from 7.1 mm downward

 

[sfol552004]

Thanks for the responses! The product is NGL's. For instance for an 8 inch line at 1480 psi, B31.4 wall thickness calc is .147 for X65. Which would allow you to use a .148 pipe, discounting corrosion allowance. It seems thin beyond a practical limit, prone to kink, dent, and or bend. Which is what prompted the question.

 

[stanier]

I have seen car exhaust tubing used for gas gathering lines in the desrt with a wall thickness of 0.016". Do the numbers including looking at corrosion, design life, risk, etc etc

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---B.B. King

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[BigInch]

I have used 8" x 0.148" and still thinner on 4" and 6" D

Independent events are seldomly independent.

 

[dcasto]

I operated 16" .109 wall bell and spigot welds. The guy who installed said they bent a few joints handling it

 

[MJCronin]

I believe that the way to approach this issue is to balance the minimum wall thickness as required by the piping code versus the calculated support span.

If a minimal wall thickness is selected, the support span may become short and the overall cost of the system will increase.

Additionally, if a thin walled pipe is used and the bearing area of the pipe support is small, additional pads may be required to distribute the load across the pipe. This will also increase cost. ( I have seen this done only on schedule 5S piping)

If the pipe wall is low and the system is hot, a stress analysis of the system is required. Thin walled piping has very high "stress intensification factors" which, in some circumstances, can require additional piping loops or expansion joints.

In some system locations, where there is a relief valve, the pipe wall must be thickened locally as per ASME B31.1 and B31.3

All of this, of course, does not address the corrosion issue which frequently pushes the designer into a thicker pipe

 

[waterpipe]

For steel water pipelines, AWWA M11 gives three formulas:

t=D/288 for sizes up to 54"
t=(D+20)/400 (sizes greater than 54 ")
t=D/240 for mortar-lined and flexible coated pipe

and says "in no case shall the shell thickness be less than 14 gauge (0,0747 in.).

The formulas are based on handling considerations.

 

[sfol552004]

Thanks for the reply's . I can use this information.

 

[JStephen]

It might be worthwhile checking on the pricing of the material, I would think at some point, there's no real savings from going thinner.

 

[LittleInch]

I also look at the allowable ovality and diameter tolerance of your pipe supply and when a pipe within tolerance can result in the wall not matching due to the thinness of the pipe then you have difficulties, e.g one pipe ID is say 400mm with a 5mm wall and another in spec pipe ID is 410mm... As many of the tolerances are percent based, smaller diameters like 12" and under can be ok in wt <0.25", but anything above that I would be very way of using that thin a pipe.

JStephen is also correct as really thin pipe and fittings like flanges can actually turn out to be more expensive and take much longer to get than a slightly thicker one due to rarity of supply. If you only have a short length you also need to allow for higher wastage due to dents, buckles, weld burn through etc.

My motto: Learn something new every day

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