Hot Tapping and Line Stopping Consideration

[marchieV]

Hello.

I just want to ask regarding the hot tapping & line stopping issues for a 66" C.S. pipe connected to a pump.
The purpose of hot tapping & line stopping is to install MOV along the line.
Our client is asking if it is necessary to perform stress analysis considering the line is connected to a rotating equipment
and the line has existing spring support and sway strut and it has also expansion joint.

My question is...
Is it necessary to perform stress analysis?

Please I need your opinions and suggestions. Thank you in advance.

Sincerely,
marchie

 

[BigInch]

You should look at it. An MOV on a 66" pipe and spring support could weigh quite a lot.

 

[LittleInch]

marchiev,

I can't really follow your query, but if the existing system is to be modified, either by installation of a tee and stopple or an MOV as well, then you are adding a lot of extra weight and stiffness if this system is hanging from spring supports.

So I think yes you should do a new stress analysis.

A diagram or drawing would help to understand your system....

LI

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[marchieV]

BI,

I don't know exactly the location of the additional MOV but they said it is after the location of the hot tapping point (refer to attached drawing).
My point is also the same, we introduce additional load that might affect the load balance of the line so the stress analysis might be needed in checking the existing condition.

Also, the maintenance team of our client(the one who will do the hot tapping) insisted that they have done it with other typical line and nothing bad happened in the pipe line BUT their design department (client side)
is asking for the integrity checking of the line. Maybe the design department is asking for assurance/safety that the pipeline is functioning well after/during the hot tapping (plus the additional MOV).

LI,

Please see attached drawing for your reference/ better visualization. I also put the dimensions and some important fittings / support conditions of the existing pipe line.

Give me some opinions. Thank you in advance.

Sincerely,

marchie

 

[BigInch]

Locating only 15mm away from what looks like a hard support would tend to not load the pipe as much in bending moment then located nearer to midspan. I can see how the operation/maintenance dept might feel comfortable about that, however I don't think the required approval to do the hot tap is their call, probably that is for engineering department, in which case I can see their reasons as well. The safest way is to do the analysis first, then, presumably, everyone will be happy with the results. At least the engineering dept will be.

 

[LittleInch]

I'm struggling to understand how you can have a 66" X 42", presumably split tee, 150mm from the centerline of a support?? Surely the support will be affected by this extra item.??

A tee of this size is a considerable additional weight, without mentioning the blind flange.

It will also stiffen up that section of line.

Maintenance and Operations teams often say things like that because to them a "bad thing" is actual failure of a pipe ( buckle, rupture etc). They don't understand that design margins exist for a reason and also that design considers situations which may only occur once or twice in its life time ( max pressure, temp, wind, seismic etc) which still needs to be considered.

It's quite along way from the spring and sway supports so won't affect them I wouldn't think, but the section impacted will be affected.

Probably OK, but difficult to be absolute without doing the analysis.

What's the design conditions / wall thickness of the 66" line? - Now that is a "Big Inch" pipe

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[marchieV]

Sorry for the wrong dimension, that should be 1500mm not 15mm. (^^)7

Actually I agree on the design margin that should be considered. Both department (Maintenance and Engineering dept.) have their own principles and limitations but in the end both dept. should be satisfied so the stress analysis should be done.

LI,

The design condition of the 66" is 90degC, 10 barg, thk = 15.88mm. It's really a "Big Inch".

Thank you for all your opinions.

Sincerely,

marchie

 

[BigInch]

Fortunately you have a relatively low pressure.
If you have a choice, keep everyone happy. Doing a quick little bit of stress analysis will go a long way to create friends. I don't think it will delay the job.

 

[LittleInch]

It is though a rather thin pipe, >1:100 D/t

Will be interesting to see if it has enough capacity for such a tee.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[rconner]

(or any heavy equipment hanging onto same in the process?)

 

[KevinNZ]

I would say the Pipe will be OK, but there will be extra loads on the supports when the hot tap equipment is attached to the tee.

 

[Gator]

Is my annotation markup below an accurate representation?

 

[DSB123]

I presume the squiggly bits either side of the bend with the spring unit are bellows units? If so then what type (hope they are tied units. Also why have the spring unit on this "isolated" bend ? Set-up looks rather strange. In any case I think you should look at the additional weight effects on the system.

 

[ADS2K6]

a Formal stress Analysis is not necessary when, one of the following situation exists as per ASME B31.8:
1) duplicate or replace without significant change a system operating with successful record
2) can be readily judged adequate by comparison with previously analysed system
3) is of uniform size, has no more than two points of fixation and intermediate restraints, and falls within the limitation of the following empirical equation:
DY/(L-U)^2 <= K

 

[Zurck]

Based from the sketch that was provided, this looks like it is the suction side of the piping to your pump. The expansion joints will not be that much affected by the additional MOV and hot-tapped fitting but because of the additional weight that you have added to the system, it will be best to run analysis of the entire suction line. The existing spring supports were not designed for this additional weight.