Gaskets for hydrotests during turnarounds

[shukrhk]

I work with an oil company and we face a particular problem during some turnarounds.

The problem occurs in hydrotesting some lines before we put the plant back to service.

and to be more specific, the isolation points of the line that will be hydrotested are ring type joints (RTJs)

and to isolate them, we use a fabricated blanking spade made out of carbon steel and we often hydrotest up to 3500 psi.

but, here is the issue:

*there is a limit to how much we can pull the two flanges apart to insert the blanking spade. Because of that we are unable to insert an RTJ blanking spade. so we use a flat blanking spade with a sheet gasket.

*the sheet gasket often cannot hold the pressure, so we have to repeat the test many times until it holds up and that often introduces some delays.

our technical support unit suggested that we start fabricating the spades from a different material (ASTM A579 Grade-73) which is supposed to allow for thinner spades and thus allows more room for an RTJs spades.

so my questions are:

1- what are your thoughts about using that different material (ASTM A579 Grade-73)

2- are there any suggestions on another gasket type that can be used just for hydrotests to seal a joint that has an RTJ flange on one side and a flat face or race face on the other.

thanks

 

[BigInch]

I think the underlying problem is that your piping engineers do not recognize that designing a configuration that allows construction make and break of RTJ flanges (or for any piping system for that matter) is very important. I've seen it extremes where even RF flanges can be difficult. You should advise your engineering department to add a provision to address this issue into your piping design and fabrication specifications.

I am not a fan of material substitutions. ASTM A579 indicates that it is for structural design of members not subject to creep. It doesn't sound like a good solution to your problem.

 

[shukrhk]

to user BigInch,

this problem does no happen with all cases, but it happens and it is too late to change it. besides designing and constructing is done by another department or maybe a contractor.

and regarding the new (temporary)fabricated blanking spades from ASTM A579 Grade-73, they will be only used during the hydrotest and will be removed once it is finished, so it won't be subjected to creep.

 

[donf]

Don't know if this will give you a dimensional advantage, but some spiral wound gasket manufacturers offer a type of sp/wd gasket that is designed to be used with RTG flanges. Be sure to verify pressured rating of the gasket and check the condition of the contact surface of the RTG flange. It doesn't seal on the groove. It's designed to seal on the "raised" face.

donf

 

[BigInch]

I am not solving your current problem, only trying to help you get your future sorted.
Add it to your company design specs that you will give to your future contractors, or your design specs that you will give to your other departments.

 

[TGS4]

The thickness of the spade is certainly an issue if you apply the B31.3 rules for determining the thickness. This paper was written to account for that - it's application could be useful in your situation.

http://pressurevesseltech.asmedigit.../article.aspx?articleid=1459628&resultClick=3