Long Weld neck flange for pressure vessel

[SKY302]

Hi
Why long weld neck fanges are used for small nozzles in pressure vessels especially nozzle size of 2"and below?

 

[metengr]

Because the particular designer of this vessel liked LWN flanges for fit-up and flow or that was the only available flange in stock at the time of fabrication. Unless you have a better guess.

 

[SnTMan]

Sometimes used to avoid making a weld seam at pipe to flange, also may be used to provide greater mechanical strength than pipe.

Regards,

Mike

 

[MikeG7]

Client sometimes has preference.
Less material items. Fewer weld. Less quality checks.
Nice and strong.
MikeG7

 

[XL83NL]

My experience for smaller vessels - say up to 10" dia; nice and strong, but (very!) expensive.

 

[jtseng123]

If giving the choice of 2" WN and LWN to any vessel vendor, I can say more than 80% of vendors will use WN, not LWN. They don't care one extra weld. Check any of your past project when LWN is not mandatory, you will find out most of the time, WN is used.

Only in two conditions we make LWN mandatory: (1) thermowell nozzle (2), client request.
Otherwise, we let vendor do what they like, and we ask (2) bracings for each nozzle for extra strength to prevent distortion for all kinds of situation.

If you have extra length of nozzle projection, especially at top head, WN will be easier to achieve. When LWN is mandatory, we will ask vendor to buy several LWNs, cut off flange and butt weld together to achieve the projection.

 

[moltenmetal]

Typically they're used for nozzles into which something will be inserted- a dip tube or some other kind of probe.- especially when you need close tolerances between the inserted device and the bore of the nozzle, or when you have a heavy nozzle load/moment. But very expensive...and a waste for something as mundane as a thermowell.

 

[InspectorJohn]

Aside from the fact that some customers specs require them, the cost comparison between the two (esp. for the smaller diameters) can be rather insignificant. In fact, there may be cases where the WN actually costs you more when you factor in the cost to make an additional weld, and potentially additional examinations of that added weld. With a LWN, you will typically get better strength (resist to moment and/or oscillations/vibration) and usually significantly more corrosion allowance due to the thicker wall, so in the end, and if you have a choice, why not use LWNs?

 

[SnTMan]

My previous employer, a small shop, always used LWN X 9" lg for 2" and under. Due to cost. One less weld, no bracing needed.

Regards,

Mike

 

[sanshu1111]

1. Smaller nozzles are a week link and specially when connected with valves/ instrument/ piping etc which are not properly supported. LWN nozzles provide better strength compare to nozzle neck made of pipe material. Strength is one of the main reason for specifying minimum 2" nozzle on the equipment in many of the client specifications.

2. Cost of one extra weld seam, gussets in case of nozzle made of pipe and separate flange. Cost factor may however differ based on fabrication/ manpower cost in the country where fabrication takes place.

Regards

Sanj

 

[GenB]

economics can be the number one reason. Design is a second reason. Some designs will just not go with std materials. And weighting the added cost of std materials a own will save time and cost. I just had a job that I could only use a lwn and the own made the miracle. Genblr.