Welded valve replacement to Flanged valve - Eng-Tips

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  https://files.engineering.com/getfile.aspx?folder=36df21b1-2fec-4c66-94af-5b2fd6eb&file=AIGA_034_06_Carbon_Monoxide___Syngas_pipeline_systems___reformated_Jan_12___(2).pdf
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. 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. OP,
I agree with Heaviside.
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 @ 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

A bit depending on service and pressure class, but some points.

a) A double or triple offset (eccentric) valve, especially in this size, will have some improved qualities compared to normal centric valves, and will be selected because of better properties for the service, or for longer lifetime/lower necessary maintenance (often case for water service for instance).

b) A flanged valve will be easier to mount and center, and mechanically a stronger construction than wafer construction. For this size, in building length compared to wafer building length, a U-shaped flange will probably also be cheaper than screwed lugging.

c) If wafer construction is selected, at least 'stearing lugs' for hanging up and centering when mounting, should be selected. The only reason to select wafer is price.

d) If water service or comparable simple service you should also check and compare price solidity/quality of construction against complete cast body form with flanges (Type EN F4, normal short valve building length or other similar standards) and only double offset (disc and stem offset, not sealing offset).

e) Final choice to be made on quality (price over required lifetime) consideration.




The U-shaped flange is the form used where the building length of the valve is the same as short building length used for wafer centric valves.

I am not sure this building length will actually exist for double or triple eccentric valves in this size. It does exist for centric valves, but anyway this flange type will fit to be installed against normal counter-flanges in the given pressure class, have the same number and shape of bolt holes, but because of the short building length of the valve you must take into consideration the limited space in how to mount (put in) the bolts and mount and screw the nuts.

See for instance for some examples. This supplier has mainly centric valves. Wafer valves are inexpensive. There is less metal and fewer machining operations. the disadvantage is that they require additional work to install. The pipes must be hung and aligned. Then the lower bolts mst be installed. the valve is then dropped between the flanges to net on the installed bolts, then the last bolts are added.

JLseagull mentioned that the exposed bolts can expand more than the valve and pipe in a fire, thus loosening the connection. COnversely, the somewhat long bolts get some pre-stretch when they are torqued in place, so most of the time the gasket loading is more consistent through thermal transients.

Lug type valves have the same face-to-face as wafer bodies. Heavier and more maching required so you pay a higher price. You get that back in ease of installation because the contractor hangs a pipe, bolts a valve on the end, and hangs another pipe. All the fussy prealignment is not required. The bolts are shielded from fire. Bolt length is critical because it's necessary to have as much thread engagement as possible, but you have to make sure the bolts don't interfere in the lugs, preventing gasket compression.

Flanged bodies are usually longer than lugged bodies, frequently (but not always) meeting a standard such as B16.10.- same as gate valves and many ball valves. At least one manufacturer offers a flanged butterfly valve series promoted as a "Quarter-Turn Gate" valve to be interchangeable with B16.10 gate valves. Even more expensive than lugged bodies, but as easy to install, and the bolt length is not critical. Clearly, wafer lugged valves will be less expensive than flanged valves, particularly when considering the reduction in bolting. Are you proposing threaded lugs or clearance lugs? If threaded, it is sometimes a pain to screw lengthy studbolts through the lugs, particularly if the lug threads have not been chased out properly and bind. Also, tapped lugged valves cannot be simply dropped out like a flanged unit. At least one adjoining spool must be removed to take out the valve.

If weight is a serious consideration, e.g offshore, then the lugged valces are significantly lighter. If there is a lugged valve out there that does not have the lugs threaded, I haven't seen it. It is customary for the 2 or 4 locating lugs in a wafer-valve to be clear-through. I can understand how a lug valve would be installed with studs, and there would be advantages in that the body would only be exposed to pure compression, but it would be a true B*tch to service. Lugged valves in my experience have threaded lugs and are installed with capscrews.

Caveat: no matter what-somebody does it the other way, too.