Schedules for LWN nozzles 1

[rajeev383]

I have a doubt regarding the pipe schedule for LWN nozzles. As per BP specification for pressure vessel "it states that all connection 2" and below shall be LWN" and other clause is that all the connection below 2" shall have a minimum schedule of 160.As per my understanding all the LWN nozzles are forged type so they shall not have anything like schedule only thickness shall be mentioned while making the datasheet.
Now what is the interpretation of the above two contradicting clause. How can I provide Schedules for LWN nozzles.
Please explain this situation

 

[GheorgheCristian]

hello, you are not alone. I've seen this in other specifications as well.In my experience , when we encounter this formulation, we use LWN for all connections 2" and below. You are right : for LWN there is no schedule.

 

[XL83NL]

Good thing, those specs. What if you have 1" pressure transmitter or thermowell? 'Hey, lets put in on of those big fat over-designed nozzles, and lets make live simpler so no one has to engineer anymore.' Oh wait, someone has to pay for it ...

 

[rajeev383]

dear XL83NL Thanks for your reply but it didn't short out my problem. I understand your concern but this is client requirement. They wont accept our design if we follow some other specification or engineering . Finally u need to take deviation costing more time and money.
So if u have solution to my query please share

 

[DekDee]

I maybe misinterpreting this but it seems pretty straightforward.
LWNs are provided with a typical OD - the ID is specified on the purchase order.

If you need to comply with Sch 160 requirements you purchase all your LWN's with an ID to match the respective Sch 160 ID it is being connected to.
The OD of an LWN is always bigger than a schedule pipe (as they are self reinforcing) so you will always comply with the Sch 160 minimum requirement for wall thickness.
Regards,
Shane

 

[SnTMan]

rajeev383, 2" Sch 160 thickness = 0.344" regardless of Class. 2" LWN thickness for 150# Class = 0.53", and increases with higher Class.

If you select LWN nozzles you will always meet both requirements, and will have one less weld to make as well.

Regards,

Mike

On Edit: If that were the worst contradiction I found in client specifications, my professional life would be much simpler & happier

 

[DekDee]

I had a 9 page "Request for Clarification" on the last project specification I was involved with and we were the client.
As the Quality Co-ordinator it makes it hard to enforce something when it is so poorly written that the kindest thing you could do would be to put a match to it.

 

[LittleInch]

rajeev383.

I agree the clause is a little odd and overdoing it a bit, but is does say sch 160 as a minimum, therefore it is not contradictory, only a little confusing.

The term Long Weld Neck, may well be in common usage, but the exact phrase which should be used is "straight hub welding flanges" see para 2.8 of ASME B 16.5.

The dimensions you need to check are for you particular flange class rating, the X dimension and the B dimension in the appropriate table in B 16.5

This will give you the wall thickness of a "LWN" flange. If its more than 8.74mm (the wt of 2" sch 160)-even class 150 is more than that-, then you've satisfied the requirement.

Not all connections on a vessel will have a flange - some could be welded pipe - depends on the duty and vessel so not quite as silly as it might sound at first.

So I would just call out a straight hub welding flange to ASME B 16.5, class XXX

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

 

[SnTMan]

...when it is so poorly written that the kindest thing you could do would be to put a match to it.

Know the feeling

Regards,

Mike

The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[marty007]

I normally interpret such statements as follows:
- Straight nozzles - LWN
- Special nozzles - sch160 pipe.

Special nozzles I think of as anything where it isn't directly flanged. These are often nozzles with elbows attached such as on vertical vessels where the nozzle is elbowed horizontally.

 

[SnTMan]

LittleInch and Marty007 make excellent points regarding non-flanged (or not directly flanged) connections, Sch 160 would govern.

Regards,

Mike



The problem with sloppy work is that the supply FAR EXCEEDS the demand