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Weld Reqmnts for Slipon flanges

Weld Reqmnts for Slipon flanges

Weld Reqmnts for Slipon flanges

We are using a 300lbrf slipon flg welded by an outside vendor. System is ~20psi-550 degF thermal fluid. The flg is extra heavy to allow torqing the bolts to get a good seal against the mating flg without bending the flgs. The flg is only welded to the pipe around the outside but looks like it should also be welded around the inside. Common sense would seem to ask for welding inside as well as outside. What codes would apply to this situation?

RE: Weld Reqmnts for Slipon flanges

My best guess would be ASME B31.3. Try Fig.328.5.2B (1999 ed)

Richard Schram
Mechanical Integrity Specialist
Pharmacia Global Supply Arecibo-P. Rico

RE: Weld Reqmnts for Slipon flanges

I think I know the answer but will ask anyway.
Where can I find the stds you refer to?
I'm going to guess I need to buy the publication,yes?
BTW did you ever own a house in HP, Illinois?

RE: Weld Reqmnts for Slipon flanges


That would be your best bet...someone at your site may have a copy, I'd check there first.

Richard Schram
Mechanical Integrity Specialist
Pharmacia Global Supply Arecibo-P. Rico

RE: Weld Reqmnts for Slipon flanges

The inside weld may or may not be required, depending upon what Code you are constructing the pipe in accordance with, and the service conditions.  Having an inside weld is considered better, but is not required for all circumstances. You should refer to the fabrication requirements of the applicable code.

RE: Weld Reqmnts for Slipon flanges

In my 20 years working as a pipefitter in a union local, it has always been "standard procedure" to "backweld" the inside of a slip-on flange to the pipe end.

RE: Weld Reqmnts for Slipon flanges

just from a commom sense point of view I agree with your standard procedure.

RE: Weld Reqmnts for Slipon flanges

Hi tomd87vr,
I wouldn’t dare to think about a possibility to mount a loose type (slip on) flange with outside welding only. You may see on the Boiler and Pressure Vessel Code (ASME VIII Div. 1) Appendix 2-4 (a) (1): “… Welds and other details of construction shall satisfy the dimensional requirements given in Fig. 2-4 …”
All acceptable forms are welded both sides except of screwed flange type.
You may look on the Pipe Flanges and Flanged Fittings Code – ASME B16.5 . I can’t find it as a Code requirement there, but I’m not able to find any example figure shows a flange welded at the outside only.
If it is very important for you to apply not more than one welding, why don’t you think of using a Welding Neck flange? It has several advantages, see on Thread378-16558

Best regards.     

RE: Weld Reqmnts for Slipon flanges

As I suggested before, you should look at the relevant code.
ASME B16.5 is not a code.  It is a component standard and it does not have requirements for welding slip on flanges.
Codes are things like B31.1, B31.3, Section VIII, etc. and each can have different requirements with respect to when an inside weld is required.  An outside weld is always required.
For example, ASME B31.3, Process Piping Code does not require an inside weld except in the following circumstances.
When the service is 1) subject to severe erosion, crevise corrosion, or cyclic loading, 2) flammable, toxic, or damaging to human tissue, 3) under severe cyclic conditions, or 4) at temperatures below -150F.  Otherwise, an inside weld is not required unless otherwise specified in the engineering design.  It is not necessary with respect to flange strength.

RE: Weld Reqmnts for Slipon flanges

Go with a double fillet weld, with the weld legs => the pipe wall thickness.  Set in the pipe enough from the face so you don't melt the edge of the gasket face [max of 1/4" from face to weld toe].

Look in your nearest Engineering College Library for the American Society of Mechanical Engineers "Boiler and Pressure Vessel Code" [Section VIII Div. 1, Appendix 2] or the ASME B31.3 Piping Code

For 550F, you may want to go to a Butt-weld [weld-neck; integral] flange to decrease thermal stresses. You may get thermal discontinuity stresses which will pop a single weld.

See J.F.Harvey "Pressure Component Construction" chapter 4, or check it using roarks tables for Cylindrical Shells [Table 30 in 5th ed] It'll probably show humongous stresses in a single fillet.

RE: Weld Reqmnts for Slipon flanges


Tom..... I guess the sum and total of the above discussion is that it is not always necessary to "double weld" slip on flanges, most everyone does it as a matter of good practice.

Chuck Becht carries a lot of authority as he has recently published a book for ASME press entitled "Process Piping". He has also been on the B31 ASME code committee for several (?) years. He is, of course, correct in his interpretation of the piping code.

However, based on my experience, here is my two cents....

With a hot thermal liquid and the slight increase in cost for the additional fillet weld, put two welds on every slip-on flange. Doesn't a "hot-oil" system count as cyclic service ?

The suggestion by "arto" that you need to consider weld-neck flanges is unnecessary.....your flange welds will not "pop"....


RE: Weld Reqmnts for Slipon flanges

how about pop = undergo excessive deformation & be highly stressed ;)

RE: Weld Reqmnts for Slipon flanges

Dealing with hot oil is a certainly a safety issue. Thermal cycling certainly doesn't help the single welded containment system. The usual low thermal fluid system pressure isn't normally an issue in the piping.  We also have asphalt piping with slip on flanges that operates up to 200 psi with daily thermal cycling. I have to vote for the outside AND inside weld of any slip on flange used for hot oil service and asphalt service. It was not heretofore specified in our standards but it is now.
Thanks to all for the input and discussion.

RE: Weld Reqmnts for Slipon flanges


Considering the temperature of your system, is a thermal pipe stress analysis being run?  Note that B31.3 Appendix D calls for a stress intensification factor (SIF) of 1.2 for double welded slip on flanges; but it can be up to 2.1 for a single-welded joint.  Just another reason to double weld it and implicitly lower your thermal stresses.

RE: Weld Reqmnts for Slipon flanges

Bob thanks for the info. Wasn't aware of that. One more good reason!

RE: Weld Reqmnts for Slipon flanges

As previously mentioned by Chuck Becht the rule on SliP-ON flanges are as follows.
ASME B31.3 1996 Edition.
308,2,1 Slip On Flanges.
(a) A Slip-on flange shall be double-welded as shown in Fig. 328,5,2B when the service is: (1) subject to severe erosion, crevice corrosion, or cyclic loading; (2) Flammable, toxic, or damaging to human tissue, (3) under severe cyclic conditions, (4) at temperatures below  -101 DegC (-150 degF).
(b) The use of slip-on flanges should be be avoided where many large temperatures cycles are expected particularly if the flanges are not insulated.
The figure mentioned above shows a a typical detail for double-welded slip-on and socket welding flange attachment welds.
Because your process in Thermal the pipe should be welded internal also.
Jonny Will

RE: Weld Reqmnts for Slipon flanges

One of the reasons for using SORF over WNRF flanges is that it is easier fitting for the boilermaker. Also the weld cannot be as thoroughly checked. A buttt weld can be radiographically examined whereas the fillet weld on a slip on cannot.

Go with the weld neck not the SORF for quality.

One thing you might like to take into account is that with hot oil systems there have been cases of cracks in welds allowing leakage of hot oil. The hot oil hits the insulation and spontaneous combustion takes place, if its a fibre based insulation. Monsanto always specified glass foam insulation and 100% radiography on all weld neck flanges. SORF's were not  to be used. But what would they know they only manufacture the hot oil.

Do  your HAZOPS and you would go near a slip on with one or two welds. Just ask your self "what will the coroner say?"

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