Assessing Freeze Damage

[mat211743]

Hello Friends, We are dealing with Frozen A106 Gr.B piping due to hydrotest water left inside the line. The plan is to run Go-No Go gauge to determine any bulging and accept if no bulging is observed. The valves will be hydrotested seperately to assess their integrity. Is there anything else we need to do to determine the suitability of the piping for service? I am not sure how to deal with welded valves? Can anybody share their experience?

 

[LittleInch]

What is wall thickness / design pressure?
Did the water have room to expand axially?
How long was the frozen section?
I
It might not be as bad as you think but stress could be concentrated at bends and supports

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[racookpe1978]

Full of water, or was it half-full except at low points?

Also: A pipe internally stressed (ballooned out) won't really change wall thickness until the pipe is very, very severely blown up radially. (It's not like pitting or localized erosion damage, but an even stretching of the entire wall surface.) Thus, measuring wall thickness is less important - much less important - than finding the places where the pipe is no longer "round" and where elbows are "bent" and distorted.

Look at the pipes above drain valves!

 

[racookpe1978]

Also: Unlike an "air" or gas system where the pipe is over-pressurized during an air test, this pipe will behave (get ballooned) locally depending on not only where the water was puddled, but WHEN each different water puddle froze and locked up the pressure. Thus, and early freezed section will "push" the plugging ice down stream and upstream, but not cause damage. Both sides of the first plugged section will NOT have that stress relief possible, so you might see two locations of damage in two separate areas on the same run.

 

[rconner]

Is pipe now normally buried or exposed/accessible, overall or at some locations (sounds like it may have been the latter, at least at one point? [The reason I ask as circumference ("pi") taping from the outside with a good quality, calibrated tape might be at least interesting?)]

 

[rconner]

[might also be interesting to get the perspectives, or draw on the experience?, of those who have done/do this (with some limitations) on purpose e.g.

http://www.superiorenergy.com/pdf/bti-services/pipe-freezing-as-an-isolation-techique.pdf

]

 

[zdas04]

rconnor,
I've used those freeze plugs and they work well enough. The theory is that the plug is too short to contain the expansion (so the expansion on freeze pushes the ends laterally instead of pushing the pipe out. It seems to be a valid theory since this process has been in use for something like 100 years.

The OP's case is somewhat different. The liquid freezing infinitely far (i.e., more than about 20 pipe diameters either side of the failure point) from a pool of unfrozen liquid has the ability to contain expansion of the fluids in the flow direction and the increase in volume must act on the pipe walls.

mat,
You didn't say how long the line is, if it is pretty short you can maybe verify integrity through visual inspection linked with UT on questionable spots. If the line is very long or any of it is buried, then the only way that you can be sure that you haven't had damage is to run a smart pig. I know that is an expensive option and scheduling it can take some time, but with any other technique you'll never be sure that you didn't take some bit of the line past the yield point.

David Simpson, PE
MuleShoe Engineering

In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual. —Galileo Galilei, Italian Physicist

 

[BigInch]

"take some bit of the line past the yield point" Nothing very serious about that, as long as any permanent expansion was limited to 2%.

If permanent expansion was limited and no cracks, no burst, what's the fuss all about now?
The time to worry about brittle fracture has past.
That was when it was frozen and under pressure stress.

you must get smarter than the software you're using.

 

[BigInch]

PS Now (since hindsight is pretty good) might be a good time to heat trace. Not good to do that repeatedly.

you must get smarter than the software you're using.

 

[mat211743]

Thanks folks for all the replies. It is above ground plant piping. It was left with full of water after hydrotest.
BigInch, my point is in line with what you said. if we dont observe bulging, the material has not gone past the yield point and it should be good for subsequent service pressure. Bulging indicates that the material is in the plastic zone undergone permanent deformation. We cant put piping in service once we have permanent deformation. is that right?
Zdas04, Is that possible for the piping to undergo permanent deformation without bulging? any other thoughts on this?
how do we deal with welded valves?

 

[gustavo2014]

You can disassemble the half body of the welded valve to hydrotest the line

 

[BigInch]

If strain was less than 2%, yes you can continue to use it. Sounds like you may have more strain than that.

you must get smarter than the software you're using.

 

[weldstan]

Do examine any small bore pipe pigtails. It has been my experience that they may well have experienced through wall damage.

 

[LittleInch]

The problem here is that you now have a section of piping which is suspect. It is entirely feasible for a line which was full of water for hydro (no air) to freeze in such a way as to expand the pipe beyond 2% strain, which is really quite difficult to measure, in a fairly uniform manner.

It really comes down to risk and long term operation as you have work hardened your material considerably, but you don't really know where other than the gross bulges or deformations. The impact is more on long term loss of fatigue and loss of ductility than no being able to handle the pressure. It really depends on the owners appetite for risk vs schedule. If you pressure test it again and it doesn't break then it is probably fit for service, but it's design life could be seriously diminished and should be slated for replacement at the earliest possible opportunity. No one wants to take the risk for some failure which you didn't find - replace it now.

Does depend on what it's planned operating condition is IMO - lots of flexing and variations in pressure and temperature in a hazardous service - replace it now. Some more benign fluids and operated at low fractions of stress or low variations in temp / pressure - think about replacing it later if it still looks round.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way