Loose type flange (lap joint) or slip-on with Titanium and C.S.
Loose type flange (lap joint) or slip-on with Titanium and C.S.
(OP)
This is a vessel made with Titanium plates (no cladding) of 13mm with two forged covers at both sides. Nozzles necks are with Titanium as well.
Vessel ID = 1800mm (70") design pressure = 13 bar (188psi) and Design Temp = 65ºC (150ºF),
Vendor is proposing that all main flanges and nozzles flanges to be C.S. and in order to avoid that C.S. to stay in contact with the fluid or any welding between C.S. and Ti, the vendor is proposing a loose type flange (lap joint) also named slip-on, as per ASME VIII app. 2 - Fig. 2-4 (1a).
I have the following questions:
1) What are the disadvantages of this type of flanges? These types are not usually specified for Vessels in refinery services (anyhow this equipment is for an LNG plant)
2) Is there any other option or a better suggestion to solve the problem of C.S. flange and Titanium cylinders and nozzle necks?
3) Bolts for these flanges are to be SA-320 (S.S.). Is this ok for this combination of materials?
4) Any suggestion with the material and type of gasket for tubeside is much appreciated.
Kind regards, and thanks for your help..!
Vessel ID = 1800mm (70") design pressure = 13 bar (188psi) and Design Temp = 65ºC (150ºF),
Vendor is proposing that all main flanges and nozzles flanges to be C.S. and in order to avoid that C.S. to stay in contact with the fluid or any welding between C.S. and Ti, the vendor is proposing a loose type flange (lap joint) also named slip-on, as per ASME VIII app. 2 - Fig. 2-4 (1a).
I have the following questions:
1) What are the disadvantages of this type of flanges? These types are not usually specified for Vessels in refinery services (anyhow this equipment is for an LNG plant)
2) Is there any other option or a better suggestion to solve the problem of C.S. flange and Titanium cylinders and nozzle necks?
3) Bolts for these flanges are to be SA-320 (S.S.). Is this ok for this combination of materials?
4) Any suggestion with the material and type of gasket for tubeside is much appreciated.
Kind regards, and thanks for your help..!
PGh.





RE: Loose type flange (lap joint) or slip-on with Titanium and C.S.
If it was me, I would specify the Lap joints with radius on inside corner and not chamfered. The stub ends (the Ti part) should be manufactured to match factory radius, but may be made longer to include the whole neck to eliminate a butt weld in pipe.
If the service is LETHAL there are rules for welding the flat ring to neck as well, although I would weld all of them as if it were Lethal Service.
Bolts and gaskets are up to you as you know what the service is...
RE: Loose type flange (lap joint) or slip-on with Titanium and C.S.
Sure, you can design Appendix 2 flanges with ANSI dimensions in solid titanium, but why would you unless the flange was wetted by the corrosive service on the EXTERIOR?
Lap joint flanges and clad blinds are standard for high alloy materials.
CS or SS backing flanges can be used depending on your external corrosion conditions. Proper backing flanges do exist and can be bought. In a pinch you can take a slip on flange and machine the correct radius at the face/ID. Failing to do this will over-stress the lap joint stub end.
On any vertical nozzles, a couple flange stops (little pieces of Ti plate etc.) plug welded to the nozzle necks will keep the loose backing flanges from slipping down and hurting anybody when the studs are removed.
RE: Loose type flange (lap joint) or slip-on with Titanium and C.S.
I am not sure I would use the SS bolting however, you should review this choice. Maybe you have a low temperature requirement, but I would avoid bolting that has a larger coef. of thermal expansion than the balance of the joint.
Metallic gaskets, except TI, may be a poor choice also due to preferential corrosion of the gasket.
This is going to be one expensive vessel.
Regards,
Mike
RE: Loose type flange (lap joint) or slip-on with Titanium and C.S.
They are just a thing you can buy. Ran into this in the past with 410SS and more recently with Cu-Ni exchangers.
Regards,
Mike
RE: Loose type flange (lap joint) or slip-on with Titanium and C.S.
However, with regard to your flange bolting materials, you may want to consider PTFE coated studs/nuts for this service.
Be careful that you purchase (and test) quality hardware from a QUALITY supplier.
http://hghouston.com/dcforum/DCForumID1/384.html#1
Ultra-premium bolting materials are available from:
h
Please finish this thread and get back to us on your final decisions..
Regards
-MJC
RE: Loose type flange (lap joint) or slip-on with Titanium and C.S.
Our process material is extremely corrosive so we have standarized on SS backup flanges flanges and studs on all piping in this process area both SS and Ti. It is a very expensive proposition to change out a corroded backup flange or studs.
RE: Loose type flange (lap joint) or slip-on with Titanium and C.S.
It seems that CS loose Lap joint Flanges are ok with the Ti vessel. I'll take in account the recommendations on this forum. Also the bolts seem to be ok in SS.
In fact this is a heat exchanger with sea water inside the channel (tubeside) and its fixed tubesheet.
On the other hand... does anybody know why some users prohibit this type of flange in refinery service? They always prefer Welding Neck type..!
Regards,
PGh.
RE: Loose type flange (lap joint) or slip-on with Titanium and C.S.
Teflon coated carbon steel bolts are good, but not fully corrosion resistant due to damage that occurs to the Teflon coating during handling and installation. Not a problem in most atmospheric conditions, however, if exposed to CT drift or sea coast salt conditions, they don't last as long as one would like, again from many years of experience in TX Gulf Coast
As for gaskets you give no process data. However, a very good gasket we use is stainless steel encapsulated in Teflon. Good rigidity and it does not have the cold flow problems of solid Teflon. We also you Grafoil gaskets with good success. The caution is if your process has chlorides you have to beware of crevice corrosion on the titanium gasket surface, and use a gasket that extend all the way to the ID of the nozzle pipe, if possible.
RE: Loose type flange (lap joint) or slip-on with Titanium and C.S.
Regards,
Mike
RE: Loose type flange (lap joint) or slip-on with Titanium and C.S.
A lap joint stub end is a pressure-retaining component just like any other flange or fitting, subject to code-prescribed materials- and weld integrity testing which depends on how the part is fabricated.
A lap joint stub end is ALWAYS full penetration butt welded to the pipe (or nozzle neck or vessel shell) it is connected to. That weld joint can be fully or spot RT'd per code. The lap joint backing flange is LOOSE- not welded to the neck at all.
RE: Loose type flange (lap joint) or slip-on with Titanium and C.S.
Most Ti lap joint stub ends are not just called up and ordered like lower alloy materials.
Most shops that are fabricating the pipe also fabricate the lap joint stub ends .
The point he was trying to make was how the lap ring is welded to pipe and not how the stub end was welded to pipe. see fig uw-13.5
RE: Loose type flange (lap joint) or slip-on with Titanium and C.S.
Every one of these I have seen have indeed been full penetration (through thickness) welded, although a partial penetration detail can be imagined. And as a corner joint they are not well suited to RT.
Regards,
Mike
RE: Loose type flange (lap joint) or slip-on with Titanium and C.S.
What you're saying is that you don't feel that the code-required inspections on this joint are adequate to detect all potential flaws. Given that the exotic materials we're talking about for the stub ends are usually GTAW welded through and through, and both sides of the weld can be readily inspected, I'm not that concerned.
RE: Loose type flange (lap joint) or slip-on with Titanium and C.S.
moltenmetal, I wasn't really speaking to the original question, for which I think a lap joint is fine, but attempting at least a partial answer to the above.
Regards,
Mike
RE: Loose type flange (lap joint) or slip-on with Titanium and C.S.
I need to design a 36" lap joint flange connection for 304SS.
I found the sketch UW-13.5 for lethal service but i don't see where it is referenced anywhere.
I need to calculate the minimum ring thickness after machining.
The welding looks pretty straight forward.. full pen.
Thanks
RE: Loose type flange (lap joint) or slip-on with Titanium and C.S.
i say generally because I have never seen a calculation done for that.....but with this crowd....ya gotta cover you butt
RE: Loose type flange (lap joint) or slip-on with Titanium and C.S.
We should be careful with correct use of terms here
We should use the term "lap joint stub ends" for the component butt welded to the end of the pipe. The dimensional standard used is MSS SP 43 for the stub ends. But the lap joint flange itself is dimensioned to ANSI B16.9.
The tables in these standards only go to 24 inch NPS.
Another ANSI dimesional standard covers the lap joint flanges above 24 inch NPS.....that is ANSI B16.47.
I do not know what standard covers stub ends in sizes above 24 inch....
Anyone ?
-MJC
RE: Loose type flange (lap joint) or slip-on with Titanium and C.S.
I don't know if there is an internet site for this and really don't care if there is one.
Would you care to re-name it to something else that is more clearly descriptive of what is being built?
RE: Loose type flange (lap joint) or slip-on with Titanium and C.S.
I have seen Process industry Practices used the term "lap ring" in their vessel specs. VECV1001 and VESV1002 for custom-designed lap joint flanges. KR Rao also used the term in his book. See page 52 on the link below...
http://bo
RE: Loose type flange (lap joint) or slip-on with Titanium and C.S.
I think this should be all that is needed, at least for this class of work.
Regards,
Mike