Welded valve replacement to 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

 

[Heaviside1925]

OP,
There can always be a risk when you change something without knowing why it was done in the first place. Do you know why butt-welded vales were specified originally? If not, you need to inquire why and the basis of that decision. Any advice I or anyone else would give you would be speculative. Are you asking benefits and disadvantages to flanged valves vs. butt weld valves in a certain service? If so, what service and piping specification are you using for design?

 

[georgeverghese]

What about the stem packing on this valve - something special to minimise H2 leakage ? What about other valves in H2 service? Is there some hot ignition source near this control valve ?
Check the hazardous area drawings to see if there are any clues, and talk to plant process safety / electrical engineers also.

 

[mk3223]

Questions to OP,
What is the reason to replace the existing welded control valve?
What is the maintenance history of the existing welded valve?
Are the U/S and D/S block valves welded or flanged valves?

 

[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.What is U/S and D/S block valves?-All valves existing are welded connection.
5.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. 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

 

[Heaviside1925]

OP,
Consider that a welded connection was determined to be required during the initial build. Replacement of the valve Should have been considered at that time. I am not saying it was and other drivers such as constructability and cost could have been the reason for welded connections. This is why finding out the history is important because it helps you determine consequences, some of which may not be obvious, of a design change.

Considerations:
-Is it acceptable to introduce two more leak points, ie, each flange, into this service, at this location?
-Are there currently other flanged valves in this service? are you creating a unique situation by installing a flanged valve in this service?
-Is adequate blocking and bleeding installed around this valve?
-Could a welded connection valve type with in-situ serviceability be selected?
- What are the consequences of a leak in this area? When you read the words strongly recommended
whenever this is possible what happens if there is a leak and someone is injured or a catastrophic incident results?
- The consideration of changing this connection should be managed by PSM and a HazOp should be performed with all stakeholders involved.

 

[georgeverghese]

See also section 5.5.1 in AIGA 034/06 on valve stem packing style / bonnet configuration for syngas service

 

[deepu78]

https://ammoniaknowhow.com/fiorda-case-study-syngas-fire-in-ammonia-plant-compressor-house/

 

[deepu78]

https://h2tools.org/lessons/ignition-syngas-leak-ammonia-production-plant

 

[LittleInch]

Replacing any valve requires isolation and blowdown / draining of that system.

Removing a welded in valve is a bit more complex for sure than simply unbolting it, but if you only do it every 10 years then its not really that bad.

You also need to consider the weight of the new flanged valve and the flanges and may need to re do the stress analysis of your system.

Plus all the risks of minor leaks at the flanges and difficulty getting it all to line up properly.

I wouldn't change it - too many consequences, both known and unknown.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[GD2]

OP,
I agree with Heaviside1925.
Syngas is highly flammable and toxic (CO). Risk to Personal life/injury and equipment is paramount.
I understand you have maintenance problem with the welded valve but that is how it is with flammable and toxic service. You must do a Risk Analysis/HAZOP and have management approval if you want to switch over to flanged type. There could be couple of safeguards requirements if you must go for flanged connections.

There is one joint type that proved very efficient when I worked in an offshore high pressure sour gas (H2S @4000 ppm) production platform. It was Vector Techlok Clamp connection. It was very effective, highly efficient mechanical joint. I would suggest that if you must go for flange type, you should use the Vector Techlok joint instead.

I would also suggest that if your project team don't go for a Risk analysis/Hazop, you should atleast test one valve with Techlok joint and monitor it before switching over to conventional flanged type.

Remember, modifying the current welded type valves with flanged type, you will be playing with risk to workers and plant equipment. There will be leak and it will be upto you and your management how much you can accept the risk.

GDD
Canada

 

[georgeverghese]

Though pressure at this location ( HT or LT shift gas reactor) is much lower than in the syn gas reactor / compressor loop (35bar cf 150bar), are you planning to install leak gas detection at these flanges for this new shutdown valve ? Any measures for leak detection at stem packing ? Do you have automatic shutdown and depressure sequence on confirmed gas detection at this location also ?

 

[deepu78]

No current plan to install gas detectors on flanges .
No existing detectors present for valve stem leak. How important is individual gas detection for these valves?
Currently there are gas detectors placed at different location at site and also regular manual check for flanges etc.

Also regarding replacement of gate valve to ball valves-Any critical issues to be checked for this valve type (Gate to ball) change. Current pipe spec do not allow this change.

 

[Heaviside1925]

OP,
I understand this is a global forum and acronyms like PSM and HAZOP may not translate. To your first question,

How important is individual gas detection for these valves?

This depends on a lot of factors. This may be of critical importance, or it may be of little or no consequence. You are not going to be responsible for writing a check to the company if the leak is of critical importance and something catastrophic happens. The people who would be responsible for writing the check should be making the decision of importance and before making that decision they are going to need to understand the risks, not just from a mechanical engineer's perspective but from the people operating the facility, the people maintaining the facility, the people who have been tasked with the safety of personnel and protection of the environment.

Also regarding replacement of gate valve to ball valves-Any critical issues to be checked for this valve type (Gate to ball) change. Current pipe spec do not allow this change.

Find out why the pipe spec does not allow this change.

I am not sure why you are hung up on ball valves. I get the feeling you think switching from gate valves to ball valves will remedy your issues surround the gate valve malfunctioning during a shutdown. It may or may not. All valve types have advantages and disadvantages and selecting the valve that most suits the requirement of your service is what piping specifications are for. There are plenty of disadvantages to ball valves when compared to gate valves and the biggest one I have seen in the field is them not functioning properly during a shut down because they haven't been maintained or exercised properly, which I suspect was the reason behind your gate valve malfunctioning. Same problem, different valve. Will you eventually get someone on this forum to say " Oh yeah! Change all your gates to ball valves, they are so much better because of all these reasons!!!" but if you use that as a basis for your decision, you are willfully stepping outside of standard engineering practice. I am not trying to be harsh, but I am cautioning against what you see as a quick easy fix to a problem leading to long term unintended consequences.

 

[georgeverghese]

At 35 bar shift gas reactor location, perhaps it is not necessary to have online flange and stem leakage detection. But general gas detection with auto shutdown and blowdown would be a good idea. Flange and stem leakage detection would be relevant at the much higher 150bar syn gas compression / reactor units. If I remember correctly, we didnt have online flange and stem leakage detection at 40bar HTS / LTS / steam reformer units in the plant I worked at in the 1980s'. Speak to your plant process safety / piping engineers also.

 

[deepu78]

The current valve is Pressure seal Parallel slide Gate Valve
See below