SMLS Pipe surface defect 3

[svi]

http://files.engineering.com/getfil...2026e33b35&file=smls_pipe_surface_defect1.JPG

http://files.engineering.com/getfil...cc2fa12a3c&file=smls_pipe_surface_defect2.JPG

The links above is the defect snap shot on the outside from a lot of API 5L X52 smls pipes 6 NPS 12 mm thickness. What could possibly have caused this? Can any pointers be given?

 

[metengr]

svi;
What is the orientation of the surface defects - longitudinal or circumferential with respect to the pipe axis.

 

[svi]

It is along the logitudinal. The snap shot is with the pipe horizontal and blast cleaned.

 

[salmon2]

x52 should be a normalized grade, so we can rule out it is quenching cracks?

 

[metengr]

Were these tubes specified to be hot finished or cold finished?

 

[svi]

The specification which is an addenda to the API 5L spec calls for the following regarding the manufacture,

The base steel to be fully killed by electric or basic oxygen process. Fine grain low hydrogen.

SMLS pipe may be manufactured from either continous cast or ingot steel.

Pipe shall be supplied either normalised or 'normalizing formed' or quench & tempered.

'Normalizing forming' is a forming process in which the final deformation is carried out in a certain temperature range leading to a material condition equivalent to that obtained after normalizing. When normalizing forming is chosen, the finishing temperature shall be greater than 780 degrees C. Pipes finished at a lower temperature than 780 degrees C shall be subjected to a further normalizing heat treatment with a minimum holding time of thirty minutes..

 

[svi]

The delivery material certificate further gives,
6" x 12.7 mm API 5L 2004

Melting process : Electric furnace, fully killed.
Billets manufacture : Continous casting.
Heat treatment : Normalized at 900 deg C for 13 min

Material also complies to NACE MR 0175.

It is also 100% Visual inspected.

 

[metengr]

svi;
Based on the information you provided, I would have a section of the pipe sent to a lab for a proper metallurgical analysis because I could think of at least two possible causes of the surface defects. Has the mill or supplier been involved? If not, you need to engage them as well.

 

[EdStainless]

Before this is cut for lab work you will want to do some NDT on the pipe. At least UT, maybe ET also.
The only causes that come to my mind are related to the steel making practice. You need to work with the mill on this.
This could be difficult because this might have been handled by multiple parties between the mill and you, but try to get them directly involved.

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Plymouth Tube

 

[svi]

Thank you metengr, EdStainless and salmon2,

An MP test was done as part of the investigation.
The original line pipe had arrived at site coated with 3 layer polypropylene. It was during the welding qualifications that some of the surface defects were noticed near the bevels. This led to the further examination of the coated surface, after removing the coating by blasting.

metengr, the UT you suggest must be to determine the depth of the surface defect? What is the ET method?
I shall suggest to go for the metallurgical analysis.

This is actually a bit too far for me as a piping material engineer. It is out of interest to know what happens despite such lengths of material specifications and inspection requirements.

Yes, I would have approached the manufacturer. But since the defect has been reported to them and the pipe lot taken off the project. The whole thing becomes political than anything else. Which is what that does not give me the access to the manufacturer.
Incidentally the manufacturer is European, not Chinese this time.

 

[metengr]

The UT is ultrasonic testing and yes, this method is to determine the depth of the surface flaws. ET is Eddy current testing, which is used real time to detect flaws in pipe during manufacture.

 

[ndeguy]

ET or ACFM (Alternating Current Field Measurement) have superior depth discrimination than manual UT for shallow surface-breaking flaws, if you wish to assess their extent into the material.

 

[EdStainless]

There are a number of shops in the Gulf coast that can do UT on a item of this size. They can characterize the size, depth, and orientation of the indication. They can also compare it to accepted reference standards and determine if it meets various acceptance criteria or not.
All manufactured material contain imperfections, the task is to figure out which ones are defects and which are simply indications. Defects are ones that could lead to degraded performance.

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Plymouth Tube

 

[MetalGuy10]

svi;
Unfortunately, politics with suppliers often play a role in a failure investigation. From your comment,
“Yes, I would have approached the manufacturer. But since the defect has been reported to them and the pipe lot taken off the project. The whole thing becomes political than anything else. Which is what that does not give me the access to the manufacturer. Incidentally the manufacturer is European, not Chinese this time.”,

you may want to request more information from the mill on the heat lot that the defective pipe was produced from. Of course the mill, is fine with removing the one defective joint, but what about the other pieces that are part of the lot? The pieces that the mill did not catch with NDT got out so what about the rest of the pieces in the lot? Many of those who have responded have noted that the defect may be related to steel making, and I would agree with the initial guess. Some steel making defects could be intermittent if they were related to inclusions that can occur during continuous casting, and intermittent defects can show up in a random fasion.

Mill markings on pipe are important for all API 5L products, but when pipe has FBE or 3 layer poly coating, the original markings are not visible. Often mill heat lot markings are stenciled in the ID of pipe that has been coated. You should start checking for mill markings in the ID, and look for heat lot, API lice #, and other marking that will help you to evaluate the lot in question. Perhaps this seems extreme, but I once saw a claim for line pipe that had leaks, and the leaks were discovered after the pipe was buried and pressure tested.

Steel surface defects can also cause a “holiday” and coating void in FBE and poly coatings if the steel surface defect is not ground before applying the coating. Another question, why didn’t the coater see the defect? The coater should also have records for the heat lot in question.