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Pipeline pipes

Pipeline pipes

Pipeline pipes

(OP)
Hi,

I have a question:
which grade of API 5L chose for pipelines? and why?
I've heard 5L grade B is not applicable for pipelines, is this expression true?

Best Regards,

RE: Pipeline pipes

"Not applicable"? Every single time I've bought new pipe for a job it has been Grade B. I've run some of the X grades in gathering jobs, but those were very special cases or when I was forced to pull the pipe for a job from the surplus list.

David Simpson, PE
MuleShoe Engineering

Law is the common force organized to act as an obstacle of injustice Frédéric Bastiat

RE: Pipeline pipes

buy whatever yield stress rating you need. If it's only 35,000 psi, then 5L-B has that rating.

I hate Windowz 8!!!!

RE: Pipeline pipes

That really is the bottom line. You should use the lowest grade that will work in your application. Higher grades have higher strength, but at the cost of toughness. Nothing is ever free.

David Simpson, PE
MuleShoe Engineering

Law is the common force organized to act as an obstacle of injustice Frédéric Bastiat

RE: Pipeline pipes

Right. Speaking of free. Everything usually comes down to a trade off between one, or more, characteristics of one material over that of another. As long as lowest grade doesn't imply higher cost for the design as a whole, one would typically expect to buy lower grade material at a lower price, however higher yield materials can reduce design weight, so if you have to move a lot of pipe a long distance from mill to installation points, pipe grades with higher yields can offer substantial economic advantages in saving freight charges alone. If that's not apparent on a given project, the pipeline just isn't long enough.

I hate Windowz 8!!!!

RE: Pipeline pipes

BI has it right. Which grade and why? - Do the option calculations and work out for your system (diam, design pressure, length, cost per tonne for each grade) which is the most efficient. Lower diameter and lower pressure tends to require a certain min thickness so lower grade material is often cheaper - just because your calculation says you need 1.36mm wall thickness on 10" pipe doesn't mean that you can either buy it or install it, therefore you need to have certain minimum thicknesses.

5L grade B , or L245 as it's now known, is a fine grade and essentially the lowest that you will find in most pipelines. It is just that you can now get L450 (X65) for not much more per tonne, but results in just over half the wall thickness / weight so for higher diameters and higher pressures has become the defacto "standard" for many longer distance pipelines.

My motto: Learn something new every day

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

RE: Pipeline pipes

Another advantage of of using a higher grade material is the lower risk of having to replace pipe segments due to class upgrades. Also, there have been situations where the overpressure protection failed in compression facilities and pipe segments were exposed to pressures greater than the originally specified material could have safely contained.

RE: Pipeline pipes

I guess that's possible, but presumably with higher yield materials, one would design for no more than the required operating pressure for any given class location and use thinner walls to avail oneself of the lesser shipping weights, hence the higher maximum pressure or class location upgrade advantages you mention would probably not be (fully) realizable, if minimizing shipping weight was the original goal.

I hate Windowz 8!!!!

RE: Pipeline pipes

SectionIX,

In addition to the point BI makes, i.e. if you design it correctly all grades have a similar ability to withstand over pressure as the lower grade material should be thicker than the higher grade. In fact the opposite is true from your supposition as the difference between SMYS and UTS tends to narrow as the grade / strength increases such that some high grade pipeline steels have a ratio of UTS to SMYS above 0.9, whereas for the lower grade steels it is closer to 0.8, thus you actually have more ultimate strength in the lower grade steel.

My motto: Learn something new every day

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

RE: Pipeline pipes

Finally, pipe grade selection is based on costs and service. Higher strength materials will have thinner walls and the costs will generally be lower even though the price per ton is greater; however, low strength grades (5LB/X42) are often used for low pressure systems or when stress corrosion cracking is of concern.

RE: Pipeline pipes

Or especially when fatigue resistance is desirable. Lower strengths result in thicker cross sections which have greater radii of gyration, which don't vibrate with such high amplitudes and offer more axial buckling resistance per pound of material, etc. Clearly lower strengths do have a place.

I hate Windowz 8!!!!

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