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Use of Sch 80 in place of Sch 40

Use of Sch 80 in place of Sch 40

Use of Sch 80 in place of Sch 40

We have a 4 NPS Sch 40 line run in our plant. At one point we need to change 3 feet length of this pipe with a new pipe. We have with us a pipe of 4 NPS Sch 80. Can we use Sch 80 pipe in a line of Sch 40. The material is same. Where i can find an article in ASME in this regard.

RE: Use of Sch 80 in place of Sch 40

Build it per plan.   (A Sch 8- pipe has a smaller internal diameter than a Sch40, and you are changing the flow characteristics of the system.  Slightly, yes.)

If you simply have to to use the wrong schedule pipe, get a design waiver in writing first.   Which will cost more than FedEx'ing a new (proper) pipe to the plant.

Butt welding two different schedule pipes is not recommended because the preps will differ.  

But you're asking in a nuclear forum about 3 feet of (cheap) pipe when the question should be/could be "Why are you having to replace three feet of pipe" in the first place?    

RE: Use of Sch 80 in place of Sch 40

Make sure you get the right end prep on the Sch 80 piece.  You will have to bevel it down to match the Sch 40 due to wall thickness.


RE: Use of Sch 80 in place of Sch 40

If this is in a nuclear plant, it will be much cheaper, simpler, faster to simply get the correct pipe than to issue the change in design for something like this.   

RE: Use of Sch 80 in place of Sch 40


The above replies reflected a lot of the regulatory issues surrounding making design changes to a safety-related pipe, especially in the US.

I believe on other threads you've indicated that you were in Asia (Pakistan??).  Therefore the regulatory aspects may well be different.  Additionally, there is nothing in your post that indicates that the pipe in question is in a nuclear safety-related system.

As racookpe1978 said, Schedule 80 pipe has a slightly smaller inside diameter.  For your 4" pipe, it will go from 3.55" to 3.36"  This will slightly increase your Reynolds number and your flow velocity.  In addition, the pipe will weigh more (per my Crane 410, the weight difference is about 3 US pounds per foot of pipe -- or a total of 9 pounds more).  You should evaluate the effects of these changes on your design, if the pipe is in a safety-related system.

However, my personal opinion is that, for a temporary change, it could be shown to be acceptable.

For everyone else, none of what I said above implies any sort of official NRC opinion.

Patricia Lougheed


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