Lamination defects in Amm piping

[mthakur]

We have a low temp CS pipeline carrying liquid ammonia at minus 33 Deg, these pipes were found with "lamination defects" which were considered to be acceptable from design view point. These defects were marked on the pipelines and need to be monitored for their growth on regular intervals form outside. We had initially welded some probles along these defects and had measured the growth using LCPD technique. It seems the LCPD doesnt work and we need to resort to some other technique, all other NDT methods such UT or MPI are not suitable as these require insulation removal which is not possible beacuse of sub zero temperature of medium. Does any one know about a suitable NDT method that can be employed to monitor these defects.
regards

 

[BigInch]

Why not simply use removable insulation at those points.

"I'm all in favor of keeping dangerous weapons out of the hands of fools. Let's start with typewriters."
- Frank Lloyd Wright (1868-1959)

 

[MJCronin]

mthakur...

What US/ISO/DIN/API specification was used to purchase the piping ?

It has been my experience that all of these piping specifications require a metalurgical process ensuring a "fully killed steel" that is specifically designed to prevent these defects.

These are very serious defects that prevent the full range of forces and moments to be transmitted through the pipe wall. Unwanted shear stresses can be developed between the laminations.

While some structural plate components can be used with laminations (e.g. steel column baseplates loaded in compression only)....piping is a whole 'nother matter.

I suggest that you re-post your question in a metalurgical forum

My opinion only...

-MJC

 

[MJCronin]

More info:

In the US, ASTM standards require "fully killed" steels for all wrought ferritic components:

http://www.astm.org/Standards/A960.htm

This Chemical engineering "rules of thumb" document seems to require a "fully-killed" construction (i.e. no laminations) for piping in low temperature service:

http://books.google.com/books?id=d9...&hl=en&sa=X&oi=book_result&resnum=1&ct=result

Remarks or comments ?

 

[brimmer]

Not sure about the classification as lamination defects... perhaps they are something else if they are growing...
I was going to suggest RT, but it is a liquid product inside the line, you might be able to get shots if you shut the line down temporarily, if these indications have depth to them you might be able to see them with RT.
Can you just put sleeves over these affected areas?
If these are simply surface breaking laminations I am not seeing an issue... it is the mid-wall non-planar laminations I would be concerned about.
Have you ever recorded growth on any of these?
I am a little ignorant of liquid ammonia and integrity concerns associated with it, normal gas/oil/water lines contain laminations in pratically every joint, both external and internal.

 

[stanweld]

Removable, insulation ports are commonly provided to permit UT examination for corrosion monitoring. Straight beam UT can be employed to determine opening up of lamination dicontiuities. Flaw growth can also be monitored by acoustic emmision with some degree of success. I assume that you are concerned with hydrogen blistering due to nacent hydrogen evolution during corrsion.

Lamination discontinuities are and were quite common in "killed", ingot cast steels without desulfurization and sulfide shape control melting practices. Laminations were often found in welded pipe fabricated from plate.

 

[mthakur]

The cross country pipeline line carries liquid ammonia at -33 deg and its 6 KM long, it is not desirable to take this offline often, as bringing it to ambient condition usually takes two months, besides lines is subjected to excessive thermal stresses during this process. It is also not possible to remove insulation online to perform UT or RT beacuse of its temperature. The pipe spec is A 333 Gr 6, the max depth of the defect is well within the desing requirement of this specification, this is valid only till these defects do not grow in size and that is why it is important to monitor them.
During construction, the line was fitted with probes and connecting cables were taken out through insulation to measure the growth using ACFM method. (You can read more ACFM on

http://www.ndt.net/article/ecndt2006/doc/Tu.3.6.5.pdf)

but it appears this method is not suitable as these probes require very thin cables to meaure very sensitive current requirement which is pratically impossible in outdoor condition. We are exploring other non conventional methods of inspecting and monitoring these defects (other than ACPD and ACFM)which will enable inspection wihtout having to remove insulation.

 

[BigInch]

I'm not convinced. Surely you can remove the insulation only for the time it takes to do the tests, then replace it immediately thereafter.

"I'm all in favor of keeping dangerous weapons out of the hands of fools. Let's start with typewriters."
- Frank Lloyd Wright (1868-1959)

 

[BigInch]

BTW, when I say remove the insulation, I mean only around the defect area, you know.

"I'm all in favor of keeping dangerous weapons out of the hands of fools. Let's start with typewriters."
- Frank Lloyd Wright (1868-1959)

 

[stanweld]

ACFM is only effective for detecting surface discontinuities and will not find subsurface lamination. If this is skin lamination (per brimmer) on the ID, the potential for stress crack growth eminating therefrom is virtually nil. If the discontinuities are ID surface, mill related slivers, scabs, seams, tears, etc., installation of removable insulation ports for UT examiantion is recommended or periodicaly smart pig the line.

 

[MJCronin]

Stanweld.

You state:

"Lamination discontinuities are and were quite common in "killed", ingot cast steels without desulfurization and sulfide shape control melting practices. Laminations were often found in welded pipe fabricated from plate."

What are the ASTM/API or other testing standards the quantify the limits on laminations within plate-fabricated pipe ?

How is this to be controlled when virtually all pipe is purchased on the internaltional market ?

Regards

-MJC

 

[stanweld]

MJCronin,
Depending on your needs, you may wish to order welded API-5LX, A-671 or A672 pipe with UT performed on the plate/skelp per A-578. You can always order low sulfur steel.

Just of note; we recently received some ASME Section I pipe spools fabricated from A106 B seamless pipe made in Poland that had some highly anamolous, severe linear discontinuities that could have been found with either Magnetic Testing or Shear Wave UT. After determining severity we scrapped the pipe spools. Quite frankly, I have never seen anything quite like it in my 40 years; only pictures would suffice but I have none. But that's the global market place. If mthakurs' pipe flaws were similar, I would recommend replacement at soonest oportunity.

 

[Millar]

For those commenting about removing the insulation and monitoring with UT. If the line is inservice, the metal temperature will be -30C. Even a small UT port will ice over preventing effective UT scanning.

 

[unclesyd]

You haven't stated the size and Sch of you pipe. If small enough you maybe able to get a corrosion or chord shot in the suspect area.

 

[mthakur]

Hi, carrying out UT inspection while line is charged is not possible due to frosting. The line is 10" Sch 40 A 333 Gr 6.

 

[unclesyd]

I believe that 10" Sch 40 is a little too big for a chord shot with Ir192.

 

[stanweld]

We have performed UT at -30C with low temp couplants.

 

[BigInch]

I'm still not convinced.

Tent and flood it with dry warm air if you have to.

"I think it would be a good idea."
- Mahatma Gandhi (1869-1948),
when asked about Western civilization