MAXIMUM NOZZLE WALL THICKNESS

[roca]

Is there an ASME or BS or EN code limit to the maximum thickness that a nozzle can be? (apart from the obvious reinforcement limits)

e.g. A 150mm thick fitted with a DN600 (24” NB) nozzle – what maximum thickness would be permitted for the self reinforced forging?

I tend to use a maximum of 2 to 2.5 x shell wall thickness as the maximum nozzle thickness

 

[vesselfab]

ASME....NO, we use self reinforced necks all the time that are waay past 2 to 2.5 times wall thickness

 

[roca]

Isn't that a problem on high-ish temperatures - you would restrain the shell probably cause cracking around the nozzle..?

 

[MJCronin]

roca,

This is a little off topic, but IMHO, there are cases where the tank/vessel designer wants very thick nozzles.

The discharge nozzle on horizontal tanks containing hydrofluoric or sulfuric acid are examples.

Thickened nozzles are recommended by process industry standards and practices

-MJC

 

[roca]

Hi MJCronin
Thanks for that.
For my info:
1. Why and when would you want very thick nozzles in tank and vessel design?
2. Why would discharge nozzle on horizontal tanks containing hydrofluoric or sulfuric acid need to be very thick? - due to brick lining weight?
Thanks

 

[vesselfab]

We use them on medium to heavy wall vessel of medium diameters with large openings. hard to get all that required reinforcement crammed in the small limits of reinforcement. Also large diameter boots where very large insert plates or reinforcing pads are not economical. We look at it this way. We require the same amount of steel to reinforce an opening, repad, insert plate, or thickened neck. We use which is the easiest, meets code and contractual requirements, and provides value in a good product for user. Thickened necks often fit the bill.

it is almost a neccessity when dealing with special services, where all welds, including nozzle attachment welds must be fully radiographed. This requires self reinforced "Q-lip" nozzles.

have a look at this site, may explain some of it, at least some of the economics.

http://www.ameriforgegroup.com/fvc/

 

[roca]

Thanks for that
However when 2 major oil companies (one USA and one European) state in their PV specs that self reinforced nozzles shall not be thicker than 2 x shell thickness then there is something in it.
I am trying to find out why.

 

[gr2vessels]

Hi roca,
I could not resist to join in. My experience and surely yours, is in the evaluation of the nozzle reinforcement for local and external loads, when the standard pipe thickness would lead you to increased the shell thickness, or to a local insert, a thicker strake, or sometimes even change the head type to cope with additional thickness requirements. Thickening the shell atracts PWHT, extra welding, extra costs, all the known miseries in addition to what you quoted originally. Take a thicker nozzle and most of your problems are solved, putting as much as possible reinforcement, per the Code geometric limits, into the nozzle neck (another issue is how to get the nozzle in time..).
I found that playing the geometric limits and the nozzle thickness, it could / may get me the most economical nozzle vs. costs of increased shell thickness. That's where I can see the limits of nozzle thickness, obviously within the mentioned Code limits. By the way, I'm unable to recall any specific clause in ASME, AS or EN restricting the nozzle neck thickness to a specific size, as noted above by the boys.
howzat,
gr2vessels

 

[roca]

Hi gr2vessels
The vessels where this is applicable are thick wall vessels.

CS vessels will require PWHT no matter how you juggle the nozzle dimensions as they will be above the normal code limit of 1.5" for PWHT requirements.

The end users have obviously found issues during operation with very thick forgings - just cos the code doesn't say anything does not mean that it is correct

 

[vesselfab]

ROCA

I have not run across that spec yet and I work for all the majors, every day. Is it in a general spec or specific spec for materials and/or services.

I will say, some materials do not lend themselves to this type of connection.

I know inconel 800H does not like these joints and I am sure others are in the same range of problems.

However, I have not run across any problems in P1 materials, our main product line, in either PWHT or non-PWHT vessels and we UT all or nozzle attachment joints.

In some services, there is no other choice, that I am aware of, where attachment welds must be 100% interpretable radiographs must be obtained. No right angle attachments, means no pads. That forces to self reinforced necks and thick nozzle necks.

 

[roca]

From one client spec (USA Oil Company):
When integral reinforcement is provided on nozzles 150 mm (6 in) and greater, the ratio of nozzle wall thickness-to-shell wall thickness shall not be greater than 2.

From European Oil Company:
Add to AD-540 of ASME VIII Div 2:
The required thickness of an integrally reinforced branch shall not be greater than twice the
vessel wall thickness at the location of the attachment.

 

[gr2vessels]

roca,
You are talking of special services, like cyclic, criogenic or other services where a significant stress will be present at the transition (thick nozzls and thinner shell), don't you? Those very good instructions were written perhaps before the FEA could predict the level of stress in the joint. Unless good engineering calculations and stress analysis can be performed on such combination (excessive thick nozzle wall vs much thinner shell thickness), the specified limits should be followed, for additional safety. However, you are user of PV Elite and I think NozzlePRO also, so what's stopping you to run the calculation and tell us how would stack-up the 2x limitation.
cheers,
gr2vessels

 

[roca]

No I am not talking of any special service - only high pressure thick wall vessels where reinforcing pads are not permitted.

These are client specs and requirements - so no amount of FEA will overcome them.

I am not a user of either PVElite or Vessel Pro - if I had a choice I would be using Compress

 

[vesselfab]

well roca, I can see having many problems trying to meet those requirements in some circumstances. How are you handling large diameter nozzles in a thick shell on these?

 

[doct9960]

roca,

Is there an ASME or BS or EN code limit to the maximum thickness that a nozzle can be?

ASME VIII: same as vesselfab's reply...NONE
BS EN 13445-3: YES. See paragraph 9.4.6 (Limitations on thickness).

 

[roca]

vesselfab
what problems do you foresee?

 

[vesselfab]

problems in basic geometry
getting require reinforcement within prescribed limits

how have you handled this?