Maintenance Procedure - Preparing Combustible Gas Vessels for Inspection, Cleaning & Repair

[MPP-LTD]

Can anyone provide feedback on how to make ensure that vessel used in Fuel Gas System are free of vapour and residue that may result in explosion so they can be handed over to maintenance for cleaning, inspection or weld repairs. The vessels would be for knock out drums and particulate filters on natural gas network for a power station. I would ideally like to here from someone who has done something similar

For Inspection:
>Gas Detector to be used at points during this procedure.
>Isolate all inlet / outlet ports using manual valves; lock valves in position.
>Vent combustible gases using flare line.
>Install additional blind plates to ensure no possibility of gas leaking by isolation valves.
>Purge vessel with Nitrogen.
>Unbolt access hatch slowly, place gas detector inside or access hatch to get reading for combustible / toxic gases.
>Put up signage for confined space.
>Allow vessel to air out for a few hours.
>Check again with gas detector.
>Vessel is ready for inspection.

If welding was to take place what else should be included?

Any feedback appreciated,

 

[Gymmeh]

So I don't know the shape of your vessel...to add any unknowns.

For my company I would need to add:
Written Procedure with valve numbers for Isolation points. Not required but, A good P&ID of the system that is marked up with isolation plan never hurt anyone.
Written procedure for the rescue plan. Doesn't need to be anything fancy, but everyone needs to know their role if there is an issue.
Depending on shape of vessels, Forced air to remove Nitorgen purge, because it will settle in low points.
Hole watch. Preferably the least heroic person on-site, you don't want them to go in to hole if there is an issue, they call the Rescue team. Which are near by the hole.
All the Confined space rescue teams I have talked to say, the main issues the have are actually, heat or cold stress, asthma attacks, heart attacks, and likes. Either way you need to get the people out of the hole.
Coutinues 4 (O2,H2S,CO,LEL) gas monitor inside hole entrance. And depending on geometry of the hole a secondary 4 gas monitor well into the whole.
Personal O2 for everyone.

If there is welding:
You need to know the details of the process gas, LEL%. Most good welders want 0 LEL% regardless of gas type.
Remeber to retest atmosphere after lunch. There was an incident in NY awhile back where a leak in a welders hoes got two guys killed when they came back from lunch.

 

[georgeverghese]

In my previous OpCo, where personnel access is required into the vessel, it is standard practice to enable free flow of air through the vessel, ie 2 manways, or at least one manway and 1 handhole open.

 

[IFRs]

You have started a good list. Check out and follow procedures for your type of vessel that have been used in the past. If this were an API tank, I'd use API publications RP 2015 Requirements for Safe Entry and Cleaning of Petroleum Storage Tanks, RP 2016 Guidelines and Procedures for Entering and Cleaning Petroleum Storage Tanks, RP 2207 Preparing Tank Bottoms for Hot Work, I'm sure there are others. You'll need your company's lock-out tag-out procedures, confined space definitions and entry procedures, SDS sheets for all chemicals ever stored in the tank, fire and rescue team considerations, etc. Entry and work inside involves life safety and should not be done casually. Depending on where you are, there should be federal, state and/or local regulations to be aware of. Your company may require more than just what you have suggested. Some require valve removal, not just closing or blinding. Some prohibit Nitrogen. Etc.
Don't invent new things here - stand on the shoulders of those who have gone before you (some have died in the process).

 

[georgeverghese]

Work of this sort is usually done under PtW (permit to work) framework - talk to your plant operations / maintenance manager on how to integrate PtW into these operating procedures. Plant operators at the control room should be aware of all such field maintenance activities, and these should be discussed during shift handover in a 24/7 operating environment.

 

[blacksmith37]

Gas free is not good enough; the vessels must contain air. I know of a few deaths caused when men entered a vessel that was gas free but was full of inert gas. Most often contractors ,not refinery personnel.

 

[chicopee]

Test for O2 and any gas components to ensure that their concentration levels are below the threshold limit values established by the American Conference of Governmental Industrial Hygienists (ACGHI)and by NIOSH. NIOSH being the testing branch of OSHA. O2 levels should be atmospheric being 18-1/2%. Which ever of these organizations have the lowest levels use that before permitting entry. Be careful about acceptable concentration levels because there are a CEILING values for certain chemicals limiting entry to 15 minutes instead of the (8)hours exposure time. Also watch out for dead air pockets as detailed by the above responders.