welded valve connection flanged valve

[deepu78]

Can flanged valve be used instead of welded valve.
Process : Water gas shift reaction
Existing design
-welded 16"(400NB) Ball (HV )control valve
-Temperature 270 deg C
-Pressure 35 Bar
-process gas line
-Material is P11 Stress relived line

Proposed change
-Replace existing welding valve with flanged valve(same size).
-The new valve weight = 2400 kg
-The existing piping class specifies Butt welded valve
-Same process condition as above

Is there a risk in this change to flanged connection ?Please advise.
DV

 

[GD2]

OP,
It's the risk of leak. Is the process gas sour?

On another note, why P11? The temp is only 270C. If this is max operating temp, the design could be @300C, still under creep for CS.

GDD
Canada

 

[deepu78]

1.Process gas is syn gas
2.Changing from 16" (BW end) Pr seal Parallel slide Gate valve(Velan)to Trunnion Mount flanged Ball valve, nitronic 50 stem material (16" Argus FK76)with Hazardous area certificate-IEC EExD IIC T4
3.All existing valves are Butt weld end.Project is to replace all 3 valves to flanged connection.
4.After 10years in service ,valve did not shut during a blackout,tried manually to close.Less repair option due to welded connection,that is the reason for flanged end.
5.The line is designed for 485 dec C that is why material is P11.Do not know why it is designed to higher temperature of 485 C than 270 deg C max temperature of operation.

5. Attaching a CARBON MONOXIDE AND SYNGAS PIPELINE SYSTEMS AIGA 034/06 GLOBALLY HARMONISED DOCUMENT I found in internet which states
-section 4.5.2
"Above-ground carbon monoxide and Syngas piping systems should follow good mechanical design
practices as applied to any other above-ground piping system. Due to its toxicity, leakage concern are
much more important than with other gases. The use of welded connections is strongly recommended
whenever this is possible. Above-ground piping should be painted to an approved specification to
protect against atmospheric corrosion."
-Section 4.7.3 case of CO/Syngas Leaks
"Unless the use of welded and below valves, unexpected leaks to the atmosphere may happen from
equipment such as flanges, and valve packings."
-section 5.4 Piping
"Welded connections are preferred and should be used wherever practical to minimize potential leak sources."

Is this document an important document or any other document/standard specifies welded connection.

DV

 

[1503-44]

Once in 10 years? How many times was the valve operated or a partial close test done during those 10 years? You may need a routine test procedure more than a flanged valve.

--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."

 

[deepu78]

1503-44 (Petroleum)
I will check.I believe all regular maintenence checks tests etc are done correctly.
My query is flanged valve can be used instead of welded valve ? IS there a safety risk?
DV

 

[1503-44]

There would be a small risk increase of leaks through the flanges. Probably manageable.

--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."

 

[SJones]

Double posted from Chemical Plant Design & Operations. Further answers are given in that forum.

Steve Jones
Corrosion Management Consultant

http://www.linkedin.com/in/drstevejones

All answers are personal opinions only and are in no way connected with any employer.