Line blinds

[athomas236]

We are involves in a natural gas fired power project in the Middle East. Gas is delivered to the plant by a 20 inch pipe that carries gas at 1000psig.

The contractor will install a single emergency shut down valve in the gas line but will not install an upstream isolating valve that will allow maintenance to be carried out on the shut down valve.

Does any one know if it possible/acceptable to install a line blind upstream of the shut down that could be used for maintenance isolation purposes.

Any advice gratefully recieved.

athomas236

 

[RPG]

It sounds like you will need to shutdown the source of material upstream to work on the valve. I am sure that there must be a valve somewhere upstream, that could be closed off. The problem with a line blind is the thickness of what would be required at those pressures.

 

[athomas236]

RPG,

The valve upstream is 5km from the plant, closing it would shut down two power stations. Hence, our investigations to find a practical alternative.

athomas236

 

[IFRs]

I don't see thickness as a problem - the blind is bolted all around with flange bolts. It may deflect a little in the middle but so what?

 

[RPG]

Before you say that the blind is bolted all around, calculate the forces on a 20" diameter piece of metal with 1000 psig pushing on it. When you go to remove it, it may look like a soup bowl and you will not be able to remove it from the flange. Most large blanks at high pressure will need a chain fall from a davit to remove and insert, because they are so massive.

 

[athomas236]

I have seen some information from a Germany supplier that claims to use a system of cams and levers to move the blind within a pair of bolted flanges which do not appear to restrict the operation of the blind.

Regards,

athomas236

 

[IFRs]

OK - so maybe "deflect a little in the middle" is an understatement when there is over 300,000 pounds [142,000 Kg] pressing on the plate. It will have to be a pretty thick plate ( 2" or more ) and the deflection may cause excess shear in the bolts unless the holes in the plate are slots and/or the bolts are high strength.

Another thought - could you remove a section of pipe to make room for a spherical shaped end to be bolted to the flange?

Heck - just instal another valve!!

 

[owg]

There is a freeze-plug method you could consider. Here is a link.

http://www.tdwilliamson.com/hottaptdw/freeze.html

HAZOP at

http://www.curryhydrocarbons.ca

 

[owg]

I forgot to mention that for gas lines, mud can be pumped in and then frozen to provide a plug.

HAZOP at

http://www.curryhydrocarbons.ca

 

[athomas236]

Thanks owg never thought of that.

Regards,

athomas236