Lamination in broken sections of tested tension specimens 1

[Frankzhou]

I found limination in broken sections of tested tension specimens when I visited our plates suppliers. The thickness of these plates are 12.7mm and 19.1mm respectively and the specimen type is 1.5 inch specimen according to ASTM A370. According to my knowledge, it is not acceptable since limination tearing could happen if these plates are used in the areas where subjected to through-thickness direction. However, no requirement in our procedures to reject these plates. What are your opinion on this issue?

 

[unclesyd]

What is the exact specification on your purchase order for the material?

I'm not up to data on the current standards but that plate would be history in my day.

 

[Frankzhou]

The designation of these is SA-738 Gr. B, 100% UTed (0% overlaped) according to SA435. The supplier explained the lamination is caused interface betweeen different microstructures, rather than nonmetallic inclusion. Since the toughness and hardness of the two microstructures are different. Cracks will be generated when the shear stress exceed the adhensive force between the two structures. However, it is dangerous even the supplier is correct. Since any courses which can introduce through-thickness stress after our receive, such as welding, deforming and fibracating etc, can result in lamination in these plates.

 

[unclesyd]

Bull Crap!

I would definately be looking for a new supplier and a new UT technician. I've never have or never would accept such a plate of any description. Just a quick look at the specifications this material has been accepted by the NRC for vessels, hopefully your supplier isn't supplying them any such plate.
I don't even like the fracture surface.

What does the MTR state?

What is the country of origin?

 

[arunmrao]

frankzhou,your supplier has been feeding you wrong information to hoodwink you . If there is any possibility, reject and ask for a replacement.

 

[Ron]

100% UT should pick up laminations. I agree. Your supplier is "selling".

 

[EdStainless]

One possibility is to have him do impacts in all three directions. And we all know which one will be poor.
This should not have passed UT, variations in microstructure will show up on UT.

= = = = = = = = = = = = = = = = = = = =
Plymouth Tube

 

[Frankzhou]

The problems are:
1. The acceptance standards in SA435 is "any discontinuity indication causing a total loss of back reflection which cannot be contained within a circle, the diameter of which is 3 in. or one half of the plate thickness, which is greater, is unacceptable." This means any discontinuity less than it is acceptable.
2. As far as I know, UT can not find such problems before the plate is stressed in through-thickness direction, caused by deforming or thermal stress.
I once worked in GL, for ship plates, all the batch will be rejected if I found lamination in broken sections of tested specimens.
Such plates will be used as reinforce plates in a pressure vessel. High level of our company asked me whether such had happened in specimens taken from plates for vessel shell which thickness is about 45mm. I donot know since such specimens are round specimens taken from 1/4 thickness of plates while lamination is often found in the middle.

 

[Frankzhou]

Following is my email to high level, I omitted the supplier's name.
I visited the supplier yesterday. I discussed with professor Z, who take charge of the development of SA-738 Gr. B plates. He explained to me that the lamination was caused by the interface between different microstructures, rather than caused by nonmetallic inclusion, especially sulfide, based on the following reasons:
1. The sulfur content of the plates is extremely low, less than 0.01% based on the information provided professor Z.
2. According to professor Z, in the middle thickness of these plates, there is an interface between GRANULAR BAINITE and BAINITE FERRITE. Since the hardness and toughness between the two microstructures are different, when the shear stress exceeds the adhesive force of the two microstructures, cracks would be generate along the interface.
However, based on my point of view, professor Z shall provide some evidences to support his conclusion, such as low power & high power metallurgical examination and Electron Probe X-ray Microanalysis of the lamination area. Even the lamination is caused by interface between different microstructures, it should also draw our attention because it can happen in deforming process during flattening in the supplier or fabrication in field. Furthermore, no matter the lamination is caused by either nonmetallic inclusion or the interface between different microstructures, my concern is that no detectable discontinuity is available in the plates before they are stressed, that is to say, we cannot find it in advance by UT. So even the supplier performed 100% UT (without overlap between each path) could not be a guarantee.
For the thicker plates, the fact that no lamination was found in broken sections of tested tension specimens is not to say the thicker plates are immune to lamination based on the following reasons:
1. As specified in 11.5.3, SA20, ASME Section II Part A, the axis of the round tension test specimen (0.500 inch/12.5mm Diameter) shall be located, as nearly as practicable, midway between the center of thickness and the top or bottom surface of the plate which thickness is greater than 3/4 inch (20mm).
2. The supplier only using the round tension test specimens (0.500 inch/12.5mm Diameter) for plates which thickness are greater than 1 inch/25mm (provided by the supplier test laboratory personnel).
3. Based on my knowledge, most lamination are caused by planar disposited non-metallic inclusions and intergranular micro cracks, which are mostly found in the middle of the plate thickness (the sections which are last to solidify). Furthermore, according to professor Z, the interface between GRANULAR BAINITE and BAINITE FERRITE is also in the middle of plate thickness.
4. Since automatic elongation measurement devices are adopted by the supplier for the round tension test specimens, neither the supplier laboratory personnel nor our inspectors will take a look at the broken sections of tested tension test specimens if they are not intend to do so.

Best regards,

Frank

PS: The serious lamination was found in the broken sections of retest specimens on Feb. 4th (as shown in fig. DSC00141 and 00147) while no lamination was found in the specimens taken from the same plate tested on Jan. 27th.

 

[metengr]

Frankzhou;
What was the heat treatment condition of the plate? Also, I would ask for metallograhic examination to determine if the observed fracture surface features are indeed caused by nonmetallic inclusions or from something else (segregation bands in the plate). This should not be that difficult to do because the supplier should be bending over backwards to satisfy your concerns.

 

[Frankzhou]

These plates are quenched and tempered. Our engineers in the US are discussing it now. The supplier would not do anything since both our purchase order and ASME Codes specify nothing on this problem. Some engineer of our company think it is not a serious problem since: 1. The lamination was found in the broken sections of tested specimens, which is subjected to tri-direction stress, such situation seldom happens in real service enviroment. 2. The stress in the brken sections greatly exceed the design stress for these plates.

 

[metengr]

Frankzhou;
Regardless, I would have a metallogrpahic examination performed of the broken pieces by an independent lab before I would accept the plate.

 

[Frankzhou]

I have been infromed that our company will receive these plates since there is no requirement to check broken sections of tested tension specimens in ASME Codes and the fact that these plates meet the requirements of NDE & mechanical tests. I have expressed my concerns of limination and have been denied because UT, PT & RT will be carried out before and after welding. I have done my job.

 

[unclesyd]

I definately would practice a little CMA on this. It has to be something besides e-mails as the IT people have been known to eliminate certain files, accidentally of course.