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Specifying Pipe Schedules for Fittings

Specifying Pipe Schedules for Fittings

Specifying Pipe Schedules for Fittings

thread378-416204: Pipe schedule vs Class rating when purchasing fittings/flanges.

The poster for the original thread referenced above was trying to standardize the information contained in some internal company database for the various fittings used in their building. Part of the challenge was when to include pipe schedules as relevant information.

This post is a word of caution regarding pipe schedules. My Tioga Pipe chart lists (3) different columns of information under the same "schedule designation" heading. Anecdotally, I think these different schedule names came from the different industries that all used pipe. Depending on who you are talking to, you may hear any or all of the designations get used.

Many different pipe schedule designations can refer to the same wall thickness of pipe. But, this is not true for all designations in all sizes. For example, in Nominal Pipe Sizes (NPS) 8 and smaller, Sch.STD = Sch.40 = Sch.40S and Sch.XS = Sch.80 = Sch.80S. When you reach NPS 10, the rules change. The NPS 10 Sch.STD = Sch.40 = Sch.40S is still true. But, NPS 10 Sch.XS = Sch.80S = 0.500" wall thickness, which does not equal NPS 10 Sch.80 = 0.594" wall thickness.

It may not be necessary to provide a wall thickness along with the schedule designation on smaller pipe sizes. But, including it can save confusion (and huge headaches) when you get into larger sizes. As one poster said, (paraphrasing) "it is better to give someone more information", they can always disregard the extra details. But, when you don't give them enough, you are forcing them to guess/make up those details or contact you for the rest of the information they need. The latter is a waste of time. The other is dangerous.


Quote: "Sometimes, the biggest problems are caused by the smallest things. Pay Attention!" (Unknown)

RE: Specifying Pipe Schedules for Fittings

Disagreed with respect.

The different pipe designations of the wall thickness, i.e. STD/XS/XXS and Sch.40/80/160, are developed in the different time through the history. As a result, some of them have the same actual wall thickness. The proper pipe thickness can be ordered from either designation. In this case, the better for the simple description of the design and PO.
The Schedule number with the suffix "S", i.e. Sch.40S/80S, is used for stainless steel pipe.

RE: Specifying Pipe Schedules for Fittings

My opinion is a mix of both previous comments I suppose. I generally summarize it to new engineers as regardless of how much you know regarding pipe schedule across any range of pipe size always confirm that the pipe schedule and wall thickness agree. There SHOULDN'T be a debate about what a 12" Sch 40 pipe means although to a layman there is room for error. I will agree that stating wall thickness clearly may prevent future confusion.

In most cases, the more accurate the better. Unfortunately, people learn and stick to generalizations. If I ask for a A312 TP316 pipe don't quote me "stainless pipe"


RE: Specifying Pipe Schedules for Fittings

Just refer to ASME B 36.10.

I agree that it can be quite odd and thickness I'd better but schedule is so ingrained in the piping world you're not going to change it.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

RE: Specifying Pipe Schedules for Fittings

IMO we only use wall thickness if the pipe is not as per schedule number in ASME B36.10/B36.19 which means we round up to the nearest commericial schedule except in cases where it is more economic to order calculated thickness which is usually in large bore and/or high pressure lines. I also dont believe that the schedule numbers are same wall thicknesses in any sizes but when you quote STD etc they can be identical in sizes from 12" upwards and as mentioned the S designation is as per B36.19 relating to SS.

RE: Specifying Pipe Schedules for Fittings

I appreciate the constructive feedback to my post. I happily accept that I was wrong about the source behind the myriad of schedules available today. I may not have been clear enough in my description of Sch.STD = Sch.40 = Sch.40S and Sch.XS = Sch.80 = Sch.80S being the same wall thicknesses. My intent was that it is only true within a given NPS size (ie. 8" Sch.STD = 8" Sch.40 = 8" Sch.40S), not that NPS 6 Sch.40 has the same wall as NPS 8 Sch.40. It is correct that some schedules are the same wall thickness across NPS sizes. But, it is far from a universal truth.

Ehzin, there is so much information (or misinformation) available that there is room for error even between professionals. You said it yourself. An RFQ asking for A312 TP316 pipe should never get a bid offering "stainless pipe." I suspect this story is based on your real world experience. Arguing that the sales rep was not a true professional (no matter how accurate that might be) does not advance the topic of conversation.

LittleInch is exactly on point. New engineers learn how to deal with the ingrained knowledge of prior generations that they inherit/adopt it themselves before passing it on to those who follow them. Changing it is as likely as the United States dropping Imperial measurements and adopting the metric system across the board.

Thanks to everyone for posting their thoughts.

Quote: "Sometimes, the biggest problems are caused by the smallest things. Pay Attention!" (Unknown)

RE: Specifying Pipe Schedules for Fittings

These are basic things you need to know to just scrape by in this industry....this is not rocket science. If an engineer doesn't know that 24" std is not the same as true sch 40, then they shouldn't be participating. Same for 12" pipe not being 12" od, but 14" pipe is 14" OD. You need to learn the road signs before they will let you drive a car.....my 2 cents.

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