Mechanical Integrity issue 2

[Corgas]

This PV (Regeneration Gas Scrubber):

Mat : SA 515-70 Thk = 0.75" C.A.= 1/16"., PWHT(1972).
Design Temp = 542 °F
Design Press = 813 psig
Accord to nameplate : Max Allow Press = 1051 psi @ 150 °F.

It was operated for a short period of time @ a temp of at least = 225 °F (temp estimated accord to paint spec, paint blistered and peeled off).

I know for a fact that for this material there wont be any metallurgical transformation @ those temps, however; it operated at higher temp for same pressure.

Do I need to perform an internal inspection to verify mechanical integrity? and/or

What type of NDE should I perform?

Thanks,

CORGAS

 

[unclesyd]

At what pressure was the vessel operating while at 225°F?

You should be alright because the material allow ables don't change at the temperatures posted. You are also covered by the design conditions if the pressure is in bounds.

 

[jte]

I presume that this is a Section VIII Div. 1 vessel?

I would not be concerned about the mechanical integrity - though you don't specify what pressure was reached during the temperature excursion.

Somehow I suspect that the terms MAP (Max Allowable Pressure New and Cold) and MAWP (Max Allowable Working Pressure) are being confused here. As long as the pressure was below 813 psig while at the estimated 225°F the vessel was operated within its design envelope. No problem. Nothing to inspect for besides ordinary wear and tear.

jt

 

[unclesyd]

Adding a little to both the above posts. If this is a common occurrence and can't be controlled by instrumentation I would consider painting it with a temperature indicating paint. The reasoning is that if the existing paint blistered and peeled off you really have no idea what the actual temperature really was, though your assumption based on the information you had at the time was in line with information at hand.

We use the temperature indication paint on all our refractory lined equipment as well as some equipment where under upset conditions we will have temperature excursions

 

[MikeHalloran]

Not many paints will blister and peel at 225F.
Check your data.
Paint something and burn it.



Mike Halloran
Pembroke Pines, FL, USA

 

[Corgas]

Thank for your prompt responses.
First, thickness is 1.75"
Second, Desing temp is 120 °F (sorry about typo errors).
This PV was designed to ASME Section VIII Div I. (1972).
Normal operating conditions are :
Operating Temp = 80 to 90F.
Operating Pressure = ~785 psig.
During the event, pressure was maintained around 785 but we don't have an exact temp (only indication is the paint). Reason for temperature excursion was finfan coolers shutdown located upstream of regen gas scrubber.
I'm not confusing terms :
U-1 form says : "MAWP = 1051 psig @ Max temp = 150 °F" and
Nameplate says : "Max.Allow Press. = 1051 psi @ 150 °F".
I checked my old pressure vessel handbook and I agree that it is under desing conditions. My next question is just "what if the vessel was operated at a temp where the max allowable stress start to decrease?.
unclesyd (Materials), excellent suggestion about temperature indicating paint.

Corgas

 

[jte]

Why not just do a paper rerate? First check to ensure that compressive stresses (dead weight, wind, seismic...) don't govern. Then check the flange ratings. You probably have Class 600 [ok, fine... for that era, "600#"] flanges in material group 1.1, so that should pass with just a bit to spare on the pressure rating.

Then re-do the calc's using the same old 17,500 psi basic allowable tensile stress.

Process the alteration through your AI and get a new nameplate for 1051 psig at 650°F. The original hydrotest should have been sufficient, so no new hydro would be necessary.

jt