COOLING WATER-SEA WATER (UNDERGROUND) 1

[MrMechanik]

Hi everyone,
In one of our projects, the FEED documents contain PMS of entire plant, so we shall follow it. In definition of "COOLING WATER-SEA WATER (UNDERGROUND)" service, the pipe material is Copper-Nickel, for small sizes(say 3/4 to 4) , GRE for 6" to 24" and API5L-B (flake-lnd at field) for 66" to 96".
The question is: In your opinion why the designer of PMS decided to change from GRE to CS (glass flake lined) for large sizes?

 

[BigInch]

Either there were too many small lines and they forgot to change them, or a higher yield strength is required for the same pressures when using those larger diameters.

**********************
"The problem isn't working out the equation,
its finding the answer to the real question." BigInch

http://virtualpipeline.spaces.live.com/

 

[MrMechanik]

Thanks BigInch for your reply,
Questions:
"Either there were too many small lines and they forgot to change them..."
What does that mean? the subject is larger size. Are you in favour of CS?
"...or a higher yield strength is required for the same pressures when using those larger diameters."
Why are you seeing in this way? the thickness can be more for GRE, but the price is much lower (half of CS, adding 20% field work for glass-flake lining.

 

[BigInch]

Just saying that, if the required GRE thickness is not practical, or cost effective for the larger diameters, a higher yield material will allow the wall thickness to be reduced.

**********************
"The problem isn't working out the equation,
its finding the answer to the real question." BigInch

http://virtualpipeline.spaces.live.com/

 

[MrMechanik]

Isn't it related to erection problem of big GRE pipes, something like leakage?

 

[rconner]

Is it possible the specifier trusted steel more for the very large lines (that I assume are quite important to the facility operation)?

 

[MJCronin]

Mr...

"GRE for 6" to 24" and API5L-B (flake-lnd at field) for 66" to 96"."

What is used from 24" to 66" ??

GRE stands for what...???

The most typical reason for selecting a lined carbon steel pipe (a fundamentally undesirable construction) is that you need the strength of steel to resist the membrane stresses developed by pressure.

-My opinion only

-MJC

 

[MrMechanik]

To rconner:
That's what i want to know, why designer is trusted to steel for larger sizes.

To MJC:
GRE stands fot Glass Reinforced Epoxy. The jump from 24" to 66" is from FEED P&ID, which doesn't include any size between.

Does anybody out there have experience with U/G erection of GRE or GRP for high flow of seawater?

 

[rconner]

You may find some of your answer by reading part of the history at e.g.

http://www.steeltank.com/LinkClick.aspx?fileticket=NndJFN+bSyE=&tabid=94&mid=452.

Basically, while I don't know much about the flake lining system talked about here (and more often see cementlinings) I believe steel has a record in even the very largest sizes you talk about here going back at least a hundred years or more. While many steel lines, and particularly in the days before modern linings and coatings, have eventually devloped some corrosion issues, I guess that record in general is still one of reasonable dependability and cost-effectiveness in carrying water and other fluids.
The other materials you talk about are much newer developments, and while they are perhaps perceived to have good corrosion resistance (and some folks like to try new things) and it won't take much web searching for you to find that they have a much more checkered/chequered performance history in even their much younger lives, and some experiences in literal infancy have exhibited problems.
Maybe the designer figures, "Better the devil you know."