7 replies to this topic

[Xpair]

Hi All,

i'm preparing some vessels entry for internal inspection and I have some troubles/questions, hoping to get your help.

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We work in a GPL plant with its inlet and outlet pipings. we process NLG to remove Butane using extraction towers and misc vessels.

the thing is for some reasons (height, insulation, etc...) we may have troubles to do a closed POSITIVE ISOLATION.

My question: is it enough for vessel entry doing as follow:

- spade the plant inlet and outlet lines
- depressurize the plant (ensure to get 0 PSIG)
- single block or double block qnd bleed to isolate the vessel

then proceed to the entry taking all other safety measures.


Many thanks and best regards,

Xpair,

[AZIZ_MN]

try this link

http://www.ncsu.edu/...d/confined1.htm

hope this will help

[breizh]

Good day ,

Safety is key and should request support from experienced people at your site . I'm sure this procedure is existing .You cannot enter any vessel without checking the atmosphere and the risk of explosivity inside the vessel .
Breizh

[Xpair]

Hi Breizh,

I totally agree with you and sure that we'll take these measures before any entry.

My enquiry is to know if the positive isolation done on the plant main inlet and outlet, the plant depressurize to 0 psig, single block around vessels, atmosphere checked, etc... are enough for the entry.

Some are requesting Positive isolation around the vessel ( " LOCAL positive isolation").

regards,

Xpair

[breizh]

Hi ,

You need to take account all the hazards and eliminate them at the their source ( all sources of energy) .
Again take advise from experienced people in your plant .
Breizh

[tarafdar]

I like to add:
1.Never rely on a single valve for isolation.
2.Depressurizing to 0 psig doesn't ensure safety.You must purge the vessel to be entered to get at
least 19.5%O₂.
3.Check for any explosive gas.

[kkala]

Without having specific expertise, I would agree with tarafdar, also assuming that the vessel has to be first purged with N2 gas to displace hydrocarbon vapors, then with air to remove asphyxiating N2 and reach the acceptable O2 content.
Nevertheless the query is whether positive local isolation shall be applied on the pipes connected to the vessel. We can see what positive isolation is in http://www.cheresour...tive-isolation/, pdf file attached to the post by fallah.
Nevertheless http://www.cheresour...ion-guidelines/ gives real information on the subject that can be assessed by the knowledgeable person (I am not). It seems to encourage positive isolation in general, but especially for maintenance reasons. Hot works inside the vessel would require positive isolation, but what about an internal inspection?
In my understanding answer depends on factors that can be assessed only on field, such as:
-How long the inspection will be? Is maintenance expected to follow immediately after it?
-Is it possible to place blinds at least on single block & bleed valve lines (already spaded)?
- Status of connected lines from maintenence viewpoint? Opinion of Maintenance Department (logically having similar experience)?
Editing note: Above supposes that lines are isolated at points near the vessel, text may mean that isolation is realized far from the vessel, near the plant. Every line should be purged, etc, after its isolation point and care should be paid for isolation to remain intact and free from vibrations (see above mentioned link). Can any branches to the line be effectively isolated? As I said I do not have practical experience.

Other memebers (having real experience) may give a more clear answer, though a generally accepted practice on the issue can be hardly found.

Edited by kkala, 25 September 2011 - 12:02 AM.

[AZIZ_MN]

Dear XPAIR,
Your question are
1). spade the plant inlet and outlet
Ans:
This is violation of confine space entry procedure, the rule says we have to provide spade on each and every vessel connected flanges( i mean to say nearest to vessel) which you are planing to enter for inspection and maintanance. hight problem or approach problem can be solved by erracting safe scafolding and insulation can be removed and fixed back once your jobs are over, and by saving this kind of maintanance cost we can not put other's life at risk.
2) depressurise the plant
ANS:
Only depressurisation is not enough, you have to decommission it properly,inertize with nitrogen and ensure that no explosive gas is present by LEL detector,if require steaming can be done to remove hydrocarbon from the system, purge the vessel with atmospheric air by mean of airmovers ( conical air educter or induced/force draft fan)