Questions You Should Know about Slip on Flange

Robert, That was going to be my question, "why can't you weld it on both sides? If it can be welded on both sides then your issue is resolved. Thanks Jim

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Thanks to all for responding, youve helped me figure some of this out. I realize just because I havent seen it here in my plant doesnt mean it can't be done. I would send a RFI to the engineer but he is going to go with whatever QA say he can do/get away with. Not perfect but sometimes that is the way it is. I can't see where it is OK to put a reducer into a slip on flange, even if its welded on both sides. How is this supported by the code? I've looked in B31.3 and this configuration doesnt conform to ASME B31.3, Fig. 328.5.2B Typical Details for Double-Welded Slip-On and Socket Welding Flange Attachment. I've suggested a weld neck flange for this application.

By

RANDER

Date

04-12- 16:06

04-12- 16:06

I agree that the configuration you describe may not be typical.  I have not seen it in the field either but it may be done somewhere.  There may be a mistake in the drawing so your RFI to the engineer is the proper course of action.  At a minimum it will show your concerns, recommendations and  it may help you in the future no matter what the engineer decides to do.

By

qcrobert

Date

04-15- 16:57

04-15- 16:57

From an engineering point of view, what argument do you propose that an ANSI/ASME B16.5, BS or API Spec 6A slip on flange to reducer (either end) to be not acceptable?

Thermal expansion, allowable stress factors, joint effeciency are not compromised by this type of joint.

This is commonly used when space limitations are considered but can be used without any consideration for space.

As far as B31.3 is concerned, it presents typical details for slip on flanges and does not attempt to address all details to be encountered in construction P&IDs.

The "Code" or any other ASME code does not attempt to "support" and (excerpt from Foreword) "is not a handbook, and cannot substitute for education, experience and sound engineering judgment."

I do admire your consideration on this issue and concurr that an RFI to the engineer is generated and logged in your book.

My past experience has taught me that RFIs and Request for Deviations to the PE brought needed attention to the issue at hand.

Keep us informed and good luck to ya,
QCRobert

By

G.S.Crisi

Date

04-15- 18:46

04-15- 18:46

qc,
1st. question: are BS (British Standards) still used? I thought that all nationals standards in Europe (BS, DIN, Afnor, SIS, UNI etc) had been replaced by ISO.

2nd question: what does RFI mean?

Thanks for the answer.
Giovanni S. Crisi

By

Date

04-15- 18:59

04-15- 18:59

"Request For Information," i.e., it is a request made to the engineer for clarification about "something."

Best regards - Al

By

qcrobert

Date

04-20- 18:16

04-20- 18:16

1.  Back in March , the national standard institutions within the EU and European Free Trade Association were obliged to withdraw all national standards that conflict with the European Committee of Standardizations suite of structural Eurocodes.

In Britain BS I will withdraw 57 national standards, including all or most parts of wellknown codes such as BS for bridges, BS for steel, BS for foundations, etc.

April , the national codes of practice for the design of buildings and civil engineering works in the UK be the 58 parts of the ten new BS EN Eurocodes.

ISO Standards are in place but have not entirely replaced the BS EN Eurocodes.

2.  Request For Info

By

joe pirie

Date

04-26- 17:39

04-26- 17:39

i've welded countless slip on flanges to reducers, 90's tees etc. If i remember correct  you can't use slip on flanges on type M pipe systyems under ASME  B31.3  
depends what code your welding to whether  its allowed or not  Joe

By

Jim Hughes

Date

05-16- 11:53

05-16- 11:53

Because the key word is typical. It also say's not every configuration is addressed. I gues I am a little confused about why you think welding slip on flanges on a reducer is a problem? Its a piece of pipe. My second question and it's something I and you should be concerned about, and that is your engineering group deferring to QC about a design issue. Sounds to me like you don't really have an engineering group.

Jim

By

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ssbn727

Date

05-19- 13:52

05-19- 13:52

Good point there Jim.

Respectfully,
Henry

Good point there Jim.Respectfully,Henry

By

Jim Hughes

Date

05-21- 15:08

05-21- 15:08

Thanks Henry.

Jim

What is a slip-on flange?

Slip-on flanges, also known as hubbed flanges, have a hub with a very low profile. This type of flange is usually connected to a pipe by one or two fillet welds (one outside the flange and one inside the flange), it is however possible to use only a single weld. Slip-on flanges are produced in many sizes and favoured for lower pressure applications (ASME class 600).

Slip-on Flange Cross Section

A slip-on flanges bore size (internal diameter) is larger than that of the connecting pipe, which allows it to slide/slip onto the pipe (slip-onto the pipe). There is no full penetration weld between the pipe and the flange, thus there are limitations for its usage due to lower weld integrity. 

However, if a welding neck flange cannot be used due to space limitations, a slip-on flange may be a suitable alternative.

Slip-on Flange

Advantages of slip-on flanges relate to lower procurement costs, less required skill for making the weld, lower accuracy requirement for pipe cutting, and no weld preparation requirements for a pipe end weld. 

Limitations for slip-on flanges relate to:

• The use of two welds instead of one (usually).
• Reduced mechanical strength (welding neck flanges are 30% stronger
• Unsuitability for cyclic loading.
• Inability to perform some non-destructive tests on welds.
• Unavailable in 2.5-inch size and over in ASME class .
• Unavailable in all sizes in ASME class .
• Generally not used above ASME class 600.

Although cheaper than a welding neck flange, there is little price difference if two welds are performed and both must be checked using non-destructive testing techniques.

 

Non-Destructive Testing (NDT) Techniques

There are no specific NDT techniques used in conjunction with slip-on flanges. If the slip-on flange is fillet welded, then a dye penetrant test may be performed on the weld. A visual inspection of the mating faces and pipe is possible.

 

ASME Standards

The standards ASME B16.5 and ASME B31.3 specify the requirements for slip-on flange installation, maintenance, and testing.

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Flange Types, Faces, and Surfaces - Explained!

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Additional Resources

https://www.pipelinedubai.com/what-are-slip-on-flanges.html

https://blog.projectmaterials.com/flanges/flange-types-piping

https://www.weldflange.com/flanges/slip-on-flange.html

https://www.trupply.com/pages/slip-on-flange

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