Flange to pipe misalignment

[hamidinho]

Greetings you all,

I'm currently working in an oil and gas project and i faced a problem , i have a 20'' Flange that the inside dia is smaller to my 20'' pipe (about 2-3 mm smaller), in ASME B31.3 is stated trimming is permissible for pipe to pipe but doesn't mention flange to pipe situation. So my question is if it's permissible to trim the flange inside dia to permit alignment or it's prohibited as per the code ?

Thank you,

 

[LittleInch]

It sounds like the flange is not supplied to match the connecting pipe schedule.

Flanges are supplied to meet the connecting pipe so long as the material strengths match.

Can you post the pipe material, schedule, flange material and what it was supplied to in terms of connecting pipe.

 

[LittleInch]

ASME B31.3 allows some flexibility for pipe alignment through trimming, it does not explicitly permit trimming flanges due to concerns about structural integrity and sealing effectiveness. It is generally prohibited to trim the inside diameter of a flange according to ASME B31.3 due to concerns regarding structural integrity and seal effectiveness; alternative solutions should be considered instead.

You need to define "trimming".

You can't modify a B16.5 flange (nothing to do with B 31.3) main dimensions ( thickness, OD, raised face dimension, bolt holes etc), but for ID it is permissible to machine the bore within certain limits specified in ASME B 16.5 to match the ID of a connecting pipe.

You can't start saying something is "prohibited" when codes normally don't do that or without providing a proper numbered reference.

I therefore do not agree with your post and suggest you edit or revise it.

 

[goutam_freelance]

From an engineering point of view it may be permitted to trim the flange provided it meets with B16.5 dimensional standards. The trimming may be considered as part of "manufacturing".

 

[hamidinho]

Hello again,
First of all sorry for the very late answer and thank you for your replies,

It sounds like the flange is not supplied to match the connecting pipe schedule.

Flanges are supplied to meet the connecting pipe so long as the material strengths match.

Can you post the pipe material, schedule, flange material and what it was supplied to in terms of connecting pipe.

I have a 20'' API 5L Gr B seamless pipe sch 20 and an 20'' FLANGE WN #150 RF ASME B16.5 SCH-20 ASTM A105N.
With many efforts from our fitters we could make the misalignment to a maximum of 1.5 mm (as per B31.3) but we still get some points on 2mm.

 

[KevinNZ]

The problem might with the pipe not the flange. Hard to make DN500 Sch 20 seamless pipe with constant thickness.

 

[Snickster]

I am not sure but I believe pipe wall taper details that are shown in B31.4 or B31.8 for different wall thickness pipe connections can be used and not be a violation of B31.3, check for verbiage in B31.3 that refers to B31.4 or 31.8 details.

 

[hamidinho]

I am not sure but I believe pipe wall taper details that are shown in B31.4 or B31.8 for different wall thickness pipe connections can be used and not be a violation of B31.3, check for verbiage in B31.3 that refers to B31.4 or 31.8 details.

Thanks for your repley i will look into it

 

[LittleInch]

Can you sketch the dimensions up as it not clear where your misalignment is.

Is it ID, wall thickness, OD, ovality?

Each one has different resolutions.

 

[hamidinho]

Can you sketch the dimensions up as it not clear where your misalignment is.

Is it ID, wall thickness, OD, ovality?

Each one has different resolutions.

It's in the ID as you may found attached (on the OD as the thickness of the pipe is not constant, some misalignment occurs).

With my small experience usually it's the opposite that happens and we just trim the pipe to match the ID of the flange and therefore remove the misalignment, but in this case i don't know if its permitted per the code to trim the flange in site.

 

[LittleInch]

What is the wall thickness of both pipe and flange at the weld point?

Can you provide actual OD, ID and wt in mm. Then we might be able to see which is the item which is out of dimensions or whether they are within allowable limits.

 

[Snickster]

Here are weld details per B31.4 2002 for uneven wall thickness connections.

 

[r6155]

Please note that the thickness tolerance for the pipe is 12.5%.