×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

S&T Exchanger - Machining Down Flange Faces
2

S&T Exchanger - Machining Down Flange Faces

S&T Exchanger - Machining Down Flange Faces

(OP)
I'm looking into a resolution for machining down a girth flange face on a TEMA/Section VIII S&T exchanger where we've found some pitting on the shell flange face where it bolts to the tubesheet. We will be replacing the tubesheet & tube bundle with a new one but have concerns about the existing shell flange face due some existing pitting that we know exists. It's been a problematic flange joint for our team to seal historically.

Can anyone direct me to where I can find how much code allowable thickness I can machine off the shell flange face before I have to weld buildup to restore the flange face?

The problem with the weld buildup path is that the metallurgy will require us to PWHT & will severely impact our schedule if we have to do this. So the hope is to only have to machine down the flange face to remove the pitting & then bolt this exchanger back up with the new bundle.

The shell was originally designed with 1/8" corrosion allowance I know. There was no machining allowance ever designed into this shell flange face though.

Thank you in advance.

Tolerance is the virtue of the man without convictions -GK Chesterton

RE: S&T Exchanger - Machining Down Flange Faces

You'll have to run the calcs to see the Code minimum thickness.

There are weld build up techniques that don't necessarily require PWHT.

RE: S&T Exchanger - Machining Down Flange Faces

(OP)
Being that this exchanger was designed in 1970, should I be looking at the TEMA code from this time? Or should I go off current Section VIII-1 now for the code minimum thickness on this shell flange?

Due to the metallurgy of this specific exchanger shell (1.25Cr-0.50Mo alloy), our standards will require us to PWHT any weld buildup we do on these flange faces.

Tolerance is the virtue of the man without convictions -GK Chesterton

RE: S&T Exchanger - Machining Down Flange Faces

Krausen, I don't suupose you have the original calculations available, but I have to ask, how do you know no machining allowance on the flange face? Do you know whether CA is applied to the face?

With these old jobs, practices were more varied than recent times.

Regards,

Mike

The problem with sloppy work is that the supply FAR EXCEEDS the demand

RE: S&T Exchanger - Machining Down Flange Faces

(OP)
SnTMan - I do not have the original calcs yet. I'm still trying to find these. I also do not know with 100% certainty that no machining allowance was designed into these flanges. That is just a guess. I'm also assuming the 1/8" C.A. that I have confirmed can be applied to the flange face.

Tolerance is the virtue of the man without convictions -GK Chesterton

RE: S&T Exchanger - Machining Down Flange Faces

Krausen, kind of a difficult situation. I suppose you could basseline your flanges using original (~1970) Code rules and allowables. I don't know if TEMA had its' own flange design rules at the time but I doubt it, it does not more recently. It did in the past have a published series of body flange designs that were listed in TEMA standards, older Ladish catalogs and perhaps elesewhere. Possible you could have these.

Anyway you could then compare calculated thickness to nominal and see if you have enough fat to face it.

I also don't see why, with approval of the involved parties, you could not perform the flange calculation using current rules and allowables to justify removing a small amount of thickness. After all this is a post construction activity.

Couple of flys in that ointment are consideration of pass-rib area and flange rigidity, which may not have been accounted for originally.

Be nice if you could find the old calcs. Best of luck,

Mike

The problem with sloppy work is that the supply FAR EXCEEDS the demand

RE: S&T Exchanger - Machining Down Flange Faces

2
1) TEMA does not require that the corrosion allowance be applied to the gasket surface of the flange, and in my experience it it's extremely rare to see a machining allowance applied to a flange designed during that era.

2) TEMA is really intended for new construction; as far as I know it doesn't cover anything with regard to remachining flanges.

3) Girth flanges for heat exchangers are typically made from forged rings designed in accordance with Appendix 2 of ASME Section VIII Div. 1. Custom forgings are usually ordered to size, so there's very little excess thickness. Manufacturers typically round up to the nearest 1/16 inch or so.

4) Appendix 2 calculations are quite conservative. In the 1968 Code the allowable stress for B7 studs was 20,000 psi, but these same studs can usually be torqued all the way to their yield point (105,000 psi) without damaging the flange.

5) Heat exchanger flanges get remachined all the time in the field without first applying weld overlay, and I've never heard of anyone requesting calculations to be submitted to confirm that the flanges still meet Code.

6) A more common issue with repeated or excessive machining of flange gasket surfaces at the shell-to-tubesheet or channel-to-tubesheet flanges is that it can affect the piping alignment by reducing the center-to-center distance between the channel nozzles and the shell nozzles.


-Christine

RE: S&T Exchanger - Machining Down Flange Faces

Great stuff from Christine74 as usual :)

The problem with sloppy work is that the supply FAR EXCEEDS the demand

RE: S&T Exchanger - Machining Down Flange Faces

(OP)
Thank you Christine74. This is the first I've heard of calc requests to confirm the girth flange still meets Code after machining down too. It's good to hear the Section VIII-1, App. 2 calcs are conservative for these, but there must be a point where machining off flange face material becomes a problem. So I will dive into this.

Very good point on potential for piping alignment issues after excessive machining down of the girth flange faces as well.

Tolerance is the virtue of the man without convictions -GK Chesterton

RE: S&T Exchanger - Machining Down Flange Faces

This seems like a very common repair for refurbished vessels and Heat Exchangers ...

Is there a Code case on this issue ???

MJCronin
Sr. Process Engineer

RE: S&T Exchanger - Machining Down Flange Faces

I'm not aware of any Code Cases but paragraph 2.3 of ASME PCC-2 covers remachining flanges. They include an option for installing a split ring on the back side to add rigidity back to the flange when machined below the required thickness.

I assume that modifying the flange in this way would be considered an NBIC Alteration.


-Christine

RE: S&T Exchanger - Machining Down Flange Faces

How deep is the pitting?
Can you send us a photo?

Regards

RE: S&T Exchanger - Machining Down Flange Faces

Krausen, since you are replacing the bundle: If you can estimate the required flange machining reasonably closely, you can compensate with increased tubesheet thickness, or perhaps by adjusting the "turn" dimensions.

The problem with sloppy work is that the supply FAR EXCEEDS the demand

RE: S&T Exchanger - Machining Down Flange Faces

Krausen
“our standards will require us to PWHT any weld buildup we do on these flange faces”.
You have two alternatives:
1)meet your standards
2)change your standards

Regards

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members! Already a Member? Login


Resources

White Paper - The Criticality of the E/E Architecture
Modern vehicles are highly sophisticated systems incorporating electrical, electronic, software and mechanical components. Mechanical systems are giving way to advanced software and electronic devices, driving automakers to innovate and differentiate their vehicles via the electric and electronic (E/E) architecture. As the pace of change accelerates, automotive companies need to evolve their development processes to deliver and maximize the value of these architectures. Download Now
White Paper - Model Based Engineering for Wire Harness Manufacturing
Modern cars, trucks, and other vehicles feature an ever-increasing number of sophisticated electrical and electronic features, placing a larger burden on the wiring harness that enables these new features. As complexity rises, current harness manufacturing methods are struggling to keep pace due to manual data exchanges and the inability to capture tribal knowledge. A model-based wire harness manufacturing engineering flow automates data exchange and captures tribal knowledge through design rules to help harness manufacturers improve harness quality and boost efficiency. Download Now
White Paper - Modeling and Optimizing Wire Harness Costs for Variation Complexity
This paper will focus on the quantification of the complexity related costs in harness variations in order to model them, allowing automated algorithms to optimize for these costs. A number of real world examples will be provided as well. Since no two businesses are alike, it is the aim of this paper to provide the foundational knowledge and methodology so the reader can assess their own business to model how variation complexity costs affect their business. Download Now

Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close