Our supplier is fabricating a ASME

[qualitypro]

Our supplier is fabricating a ASME vessel in critical service using 2:1 elliptical head of P11 material. They intend to use the crown and petal design to fabricate this. Is there any limitation to use this design per ASME code? What is the recommended design for head fabrication? Appreciate your inputs.

 

[SnTMan]

critical service

Please define

They intend to use the crown and petal design to fabricate this. Is there any limitation to use this design per ASME code?

No

What is the recommended design for head fabrication?

One piece (seamless) if possible, built up if not.

Regards,

Mike

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

 

[TGS4]

Size? Thickness? Pressure? Temperature?

 

[qualitypro]

@TGS4
Vessel diameter-4420mm
Dish blank dia- 5400mm
Dish nominal thickness-68 mm
Design pressure- 510 pig
Design temperature- 850F
Material is SA387 Gr.11 Cl.2

 

[marty007]

In my experience large diameter semi-elliptical heads are normally fabricated by first welding together flat plates to form the required blank, then the large plate is formed to the semi-elliptical geometry. These are not normally formed in the crown and petal method because of the complex crown/knuckle geometry. Forming the petals would be very difficult to get to line up properly.

I normally see the crown/petal geometry used in hemispherical head geometries where you have a consistent internal radius. As long as the internal surface radius is the same on all pieces, it will fit together properly.

Cheers,
Marty

 

[Don56]

There are very few head manufacturers that can make a head this size, this thick from a welded blank. Those that can will most likely need to do it hot (heating above the lower critical and tempering temperature). Welding and forming the round center section can be done as if forming any SE head. The knuckle and SF segments can be formed and checked with a template as hemi segments are. Even so, forming them cold because of the thickness is difficult. The knuckle segments will experience greater than 5% fiber elongation requiring stress relieving.

 

[r6155]

@ qualitypro
Your supplier is correct.

@ marty007
Impossible to manufacture as you say in this case.

Regards

 

[qualitypro]

@ SnT Man..thanks. The critical service here is that it is in Hydrogen service with about 60% H2.

 

[SnTMan]

qualitypro, off top of my head, Code (at least VIII, 1) does not address such service in any fashion. Otherwise I'd say you are getting great advice from the other posters...

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

 

[r6155]

ASME VIII does not prohibit hydrogen service.

Regards

 

[marty007]

@ marty007
Impossible to manufacture as you say in this case.

Can you provide a reason?

A few years back our shop procured a head that was slightly smaller at 4115mm ID, but thicker at 76.2mm thk. It was manufactured by welding two plates together in the flat position then forming the head to the S.E. shape.

 

[Don56]

Marty,
Was it Q&T material? Was it hot formed? Was it re-Q&T'd after forming? Were mechanicals run on specimens heated with the part(s)?

 

[marty007]

Marty,
Was it Q&T material? Was it hot formed? Was it re-Q&T'd after forming? Were mechanicals run on specimens heated with the part(s)?

It was just carbon steel (SA-516-70). The head was hot formed. The entire rest of the vessel was also subject to PWHT at the end. Production coupons were run and subjected to the same PWHT cycles with mechanical tests performed afterwards.

 

[r6155]

marty007 Sorry. You are correct.
I found a head manufacturer:
Cold formed with weld seam: D=3400 -6500 mm t=10-70 mm
Hot pressed multi-piece: D= 4000 - 12000 mm t=10-170 mm

Regards

 

[SnTMan]

Manufacturers and tooling come and go. My last company had an S&T exchanger design they built replacements for periodically. It used a pair of flanged only heads for a distributor belt. Last time I worked on an order we find the head supplier has discarded the tooling. Due to company policies stuck with the "approved vendor". Had to substitute a 2:1 head. "Real estate" was troublesome.

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

 

[qualitypro]

@ Marty007 and SnTMan..thanks for your feedback. Hopefully we should be able to find a head supplier who we can source it from. Will keep posted.

 

Last time I worked on an order we find the head supplier has discarded the tooling.

Am I correct in reading this as 'the Chapter 11 bean counters ordered useful tooling to be discarded at fire sale prices.'?

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."

 

[SnTMan]

IM, I don't know if Chap 11 was involved or not, I'd guess more like the 5S fad. The company I worked for at the time 5S'd to the point there was not a spare pipe plug or hex nut lying around.

Something got lost or broken, well you just reordered and....waited

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

 

SnTMan,
I started reading your link but had to stop before my head exploded

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."

 

[SnTMan]

Lucky for you

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