Are 1/2" pipelines reliable for process streams?

[DoItForYourself]

Hi,

Last year, I had designed 1/2" LTCS (Low Temperature Carbon Steel) pipes for a sample point (for propylene). The mechanical engineer recommended that we increase the diameter of the pipes, because as he said this size is used only in tubing and for instrumentation reasons and not in process or other streams. However, the company that built the plant had constructed many sample points with pipes of this size (Note : The pipes are supported adequately).

Our department finally supposed that the problem is that the lines of this size are not reliable enough and decided to construct 3/4" pipes for the sample point. Now, the new sample point is in place and operates without problems.

But the question still remains : Are 1/2" pipes reliable and suitable to be used for sample points? And why?

If anyone has any experience on this subject, they are welcome to express their opinion.

Thank you

 

[russ_watters]

What does "reliable" mean in this context.

This sounds to me like a personal preference issue.

 

[DoItForYourself]

I think they meant that fouling or clog may occur easier because of the small size of the pipes. In my opinion, if the service is clean (like propylene), there is not any problem. In addition, all the sample points have been operating successfully since 2000.

Perhaps, if the service is a heavy hydrocarbon (for example tar or asphalt), clogs may occur and that's why they avoid small pipe sizes (smaller than 3/4") in the refinery.

I was just wondering if there is another reason that small pipes must be avoided.

 

[Tom.G]

I was just wondering if there is another reason that small pipes must be avoided.

Could be due to operating pressure or corrosion life, the wall thickness of the 3/4" pipe is greater than the 1/2" pipe. See "ANSI B31 Code for Pressure Piping" (or its successor if there is one, this is from an old reference.)

 

[DoItForYourself]

Could be due to operating pressure or corrosion life, the wall thickness of the 3/4" pipe is greater than the 1/2" pipe. See "ANSI B31 Code for Pressure Piping" (or its successor if there is one, this is from an old reference.)

This would be a possible problem.

However, the piping specification (which states clearly that it is in compliance with ASME B31.3-Code for pressure piping) states that the size range for the pipes of this class is 1/8" - 20". The design pressure, the design temperature and the corrosion allowance are the same for all the pipes of this class (from 1/8" to 20") and go above our needs.

So, I would say that there would not have been any problem, even if I had used 1/8" or 1/4" pipes. The only difference would have been the time needed to fill the sample cylinder (more time to fill it).