Pipe schedule vs Class rating when purchasing fittings/flanges. 2

[djdalfaro]

[edited]
Good morning,

New member here, I am new in my field and currently working on updating the pipe specs at my plant. Part of this project involves setting up new material numbers with short descriptions, which are then sent for purchasing. One of the problems I have run across is not being sure when a pipe schedule needs to be specified alongside the fitting/flange rating. It appears to my novice eyes that SCH rating is needed for BW fittings/flanges, but CLASS rating is needed for SW/THRD fittngs/flanges, with few exceptions. However I know that SCH rating changes the bore size and could cause turbulent flow if not matched. Do manufacturers take this into account? I am running across a large number of different items in the specs (just about every fitting/flange used in a commercial plant), and have access to and have read the relevant ASME, MSS standards, but would like some clarification from someone in the industry. I want to verify what is correct in practice. For example, I can specify that a coupling is 3000 CLASS rating, do I also need to specify that it will be used with SCH XS pipe? Is this information that the distributer needs to get me the correct part? Another example olets, I know that BW olets are rated by pipe schedule, while SW and THRD olets are rated by LB class. Would I need to specify that a 3000 CLASS SW Elbolet would be used on STD x XS pipe? Would it make a difference in the part I received? I have compiled the list below, and would appreciate a reply as to whether I've got it right or not. As you can see from the table below, the majority of the fittings/flanges are classified by CLASS, does this mean that the SCH rating of the pipe is not needed when ordering?​

Thank you,
Damon Alfaro


[tt]FITTING__________CLASS_____________SCH RAT
CAP______________X_________________N/A
COUPLING_________X_________________N/A
ELBOW, SW________X_________________N/A
ELBOW, THRD______X_________________N/A
BLIND FLANGE_____X_________________N/A
SLIP ON FLANGE___X_________________N/A
SW FLANGE________X_________________N/A
THRD FLANGE______X_________________N/A
WELD NECK FLANGE_X_________________X
WNORIFICE FLANGE_X_________________X
SW RED INSERT____X_________________N/A
THREADED PLUG____N/A_______________N/A
CONC RED, THRD___X_________________N/A
EQUAL TEE, SW____X_________________N/A
EQUAL TEE, THRD__X_________________N/A
RED TEE, SW______X_________________N/A
RED TEE, THRD____X_________________N/A
UNION____________X_________________N/A
ELBOLET, BW______N/A_______________X
ELBOLET, SW______X_________________N/A
ELBOLET, THRD____X_________________N/A
LATROLET, BW_____N/A_______________X
NIPOLET, BW______N/A_______________X
SOCKOLET_________X_________________N/A
THREDOLET________X_________________N/A
WELDOLET_________N/A_______________X
[/tt]

 

[XL83NL]

Good questions. I would start by looking at the relevant standard to which you're specifying/purchasing a fitting. That standard (usually B16 series or MSS SP-series) talls a LOT (if not all) about how to specify a fitting.

 

[europipe]

Nobody in the neighbourhood that can help you?
I think you're totally on the wrong track, first you need to have the pipespecs with pipe and schedulenumbers. Then you seek the fittings to it.
Can't you borrow them from another company?

 

[DSB123]

You really need to read the Codes. There is no such thing as a LB class rating. For flanges there are Class 150, 300, 400 ,600 etc (Note not LB) just Class 150, Class 300 etc. The same applies to Socket Weld fittings Class 3000, Class 6000 (Not Class 3000 LB). Get the identification right first then move on!!!

 

[DSB123]

europipe,
you say "Can't you borrow them from another company? ". That is tantamount to theft!!!

All fittings that are to be butt welded to the pipe need to have the schedule specified (e.g. 8"nb Sch40 Class 300 WNRF Flange). For a reducer you need to specify the schedule at the large and small end.

 

[djdalfaro]

Thank you for the quick responses.

XL83NL - Thank you, I have read the relevant standards, but questions remain as to practice.

europipe - Thank you, I have the pipe specs, I am currently in the process of ensuring the material is described correctly for purchasing.

DSB123 - Thank you, I see my mistake, I'm not as familiar as I should be with the codes to recognize the blatant error. My post has been edited. I obviously have more reading to do.

​

 

[djdalfaro]

So I found part of my answer. The situation is as follows. Currently a project is being designed with 3/4IN SCH 80S Alloy 20 piping. We need a 150 CLASS SW RF Flange. Distributer asked planner what bore on the flange would be. OD of 80S pipe is 1.050IN, WT is 0.154IN, so bore would be 1.050-(2*0.154)= 0.742IN. Double checked ASME B16.5 Table II-8, which calls out bore as 0.82IN [note 7]. Note 7 clarifies, "Dimensions in Column 13 correspond to the inside diameters of pipe as given in ASME B36.10M for standard wall pipe. The thickness of standard wall is the same as Schedule 40 in sizes NPS 10 and smaller. Tolerances in para. 7.5.2 apply. These bore sizes are furnished unless otherwise specked by the Purchaser." Verified the WT for 3/4IN SCH 40 pipe as 0.113IN, so bore on SCH 40 flange would be 1.050-(2*0.113)= 0.824IN.

So, it seems if the flange is to be used with any schedule other than SCH 40 on CLASS 150 flanges, it would need to be noted. For consistencies sake I will note the bore for all flanges other than blind flanges.

Thanks for letting me bounce my thoughts off you guys, and replying so quickly.

 

[BigInch]

Good idea to avoid discrepencies. Many pipe sizes can be purchased that [highlight #FFFFFF]DO NOT[/highlight] correspond to standard schedule numbers. Always include the bore dimension for flanges (xcept blind) and wall thicknesses for both fittings and any welded flange necks, in addition to the standard schedule when a schedule is indeed applicable.

 

[XL83NL]

What's the point in specifying bore for a slip on or socket weld flange? Or am I missing something here?

 

[BigInch]

I assumed that one would know that it wouldn't be necessary for SO or socket welds.

 

[XL83NL]

The last post by the OP didnt indicate so, nor did you mention it in your reply, hence the question.

 

[djdalfaro]

BigInch - Our distributer requested the bore on the SW flange I mentioned in my post. Is that not something that is normally requested? I understand that it wouldn't be required for a SO flange.

 

[moltenmetal]

Bore is required for a SW but not a SO flange. We standardize on one bore for all SW flanges because we stop at 2" and all SW flanges have a crevice and aren't free draining anyway- a minor difference in ID of the flange itself makes no practical difference.

 

[europipe]

DSB: "Can't you borrow them from another company? ". That is tantamount to theft!!!
Don't be so dramatic,it's not topsecret. you need to do the calcs anyway.

 

[DSB123]

europipe,
It's not being dramatic as you say. It takes time and effort to create pipe specs and then you encourage someone to plagerise the results. Not the professional way forward in my eyes and not something that should be promoted!!!

 

[LittleInch]

Repeating a lot of what is said above,

Flange class ratings to ASME B 16.5 are steps - correct terminology is ASME class xxx or API xxxx. Common terminology used is e.g. 600lb, #600, but for MTos and orders use the correct designation.

In general you need to specify the connecting pipe when it is being butt welded to the fitting.

Socket weld and threaded connections should only require the OD, which is unaffected by wall thickness.

The example you quote may be an odd ball or maybe if the wall thickness is small, they machine the bore back to match the ID?

If in doubt tell them what it is.

Schedule numbers and descriptions like STD, XS, XXS etc exist for piping. Pipelines and some long piping runs could easily use wall thicknesses which don't correspond to a standard schedule or descriptor like BI says.

Also some piping systems will have pipe wall thickness which are not valid for the flange rating. You don't need to have the design pressure of a system fixed by the flange rating. Some companies do this, but if you don't need the metal, it's a waste buying it. E,g, you can have a design pressure of 70 bar, which needs a class 600 flange, but has pipe of a thickness only for 70 bar.

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

 

[DSB123]

LittleInch,
Please show me where in ASME B16.5 a flange is designated as 600LB or #600 ? Flanges are designated Class 600 (without the Lb or #)

 

[MickMc]

Common practice is to state in Sch/Thickness column " Thickness to Match Pipe" for butt weld and "N/A" in same column for Socket Weld and Threaded. SW and THRD would be addressed as ASME Class Rating in same column as flanges according to B16.11 Table 2 commonly 3000 or 6000 depending on wall thickness/schedule required.

 

[BigInch]

This has been accepted custom in my neighborhood for more than 50 years, regardless of what might be found in any edition of 16.5 or 16.34

ASME#followed by class designation, such as "ASME#600" should be used to eliminate any confusion from WOG 2000 LB (actually psi) ratings which are working pressure limit based, such as this valve here using a "WOG 1500" and "WOG 2000" (in psi) ratings,

http://www.astech-valve.com/s/en/2/...4-inch-~-2-1-2-inch-A-355R-A-355F-364266.html

Using numbers alone, without any accompanying ASME or WOG designation, risks generating dangerous errors.

While IT geeks might prefer to state minimal information MY personal preference is to state everything, even if it might appear to be somewhat redundant. I'd rather be redundant than have somebody confuse 1500# with 1500

size
item
spec and number,
pressure rating, with unit
OD
WT, with unit
std schedule when applicable,
bore when applicable
material spec

EXAMPLE:
16", FLANGE, RFWN, ASME B16.5 #600, 16" OD x 0.250" WT, SCH40, Bore 15.500", ASTM A105N

 

[DSB123]

BigInch,
It may be accepted custom "in your neighbourhood" to use LB or # but actually it is incorrect. Nowhere in ASME B16.5 does it refer to 150Lb or 150# - if it does then please correct me!! As an Engineer you should move with the times - years ago people used to use Lb or # but times have moved on and engineering should use the correct designation. It's the same as people still using ANSI B16.5 - there is no such standard as ANSI B16.5 - do a search on any Standard site if you do not beleive it.