Plate materiel Through thickness test area reduction percentage . 2

[Arulkumar P]

One of my client specification is asking "CS & LTCS ( Boiler Quality) plate above 50 mm is required through thickness test as per SA 770 shall be conducted and minimum reduction in area of 35% shall be ensured."

Clause 5 of acceptable standard SA 770 in ASME Sec IIA part A code shows "test shall have a minimum reduction of area no less than 20 %."

Clause 3.9 of Sec VIII Div 2 shows "For carbon and low alloy steels, the reduction of area shall not be less than 30%"

My query is

1 what is the background of the CS & LTCS (BQ) Plate through thickness test percentage reduction area minimum 20%,30%&35% or higher?

2.what is the high alloy materiel( i.e.-Stainless steel and nickel alloy steel)through thickness test percentage?

 

[DBreyer]

Defining a higher percentage is sometimes specified as a way to ensure steel cleanliness.
Laminations and inclusions (manganese sulfide,...) tend to lead to a more brittle failure mode through the thickness combined with only minimal area reduction.
We sometimes specify the additional requirement if there is a potential for hydrogen induced cracking due to the service environment (wet H2S).

Teh code requirements you mentioned arerealting to the transverse or longitudinal tensile tests. Through thickness testing is usually not required by pressure vessel codes but an additional requirement for certain environments.

 

[Arulkumar P]

Thanks for your reply

Yes, our requirements are wet H2S services in refinery Application.

I have checked all the material testing client requirements.

The materials are CARBON STEEL,STAINLESS STEEL,DUPLEX STAINLESS STEEL, Incoloy 825,Inconel 625.

Through thickness testing is requested only for carbon steel material and other material through thickness testings is not requested.

CS testing requirements are [highlight #FCE94F]"THROUGH THICKNESS TENSION TEST (FOR PLATES) Plates 25mm and above in thickness shall be tested perpendicular to the rolled, surface with frequency and test procedure as per ASTM A 770 and determination of reduction of area as per ASTM A370. Minimum reduction area shall not be less than 35%."[/highlight]

As I understand the above your reply. ensure the steel cleanliness and minimum lamination and inclusion is applicable only carbon steel materials which is used in H2S service for comply the Minimum reduction area shall not be less than 35%

My understanding is correct?

Also why client is not asking through thickness test requirements for other materials and shall we not ensure the steel cleanliness and minimum lamination and inclusion for other materiel.

 

[DekDee]

I am presuming you are talking pressure vessels for the CS ?
What about all the other materials - piping or vessels ?
On the CS vessels do you have weld joints that may be under high restraint ?
I am not familiar with ASTM A770 but in the structural field the testing is Z15, Z25 & Z35.
The requirement for through thickness testing (Z testing) is nominated by the design engineers based on the loading at specific weld joints.
Hope that helps,
Cheers,
Shane

 

[Arulkumar P]

My query is related to plate material requirements which is used in the pressure vessel on the wet H2S services refinery application.

For CS and LTCS pressure vessel Material of construction ( CS MOC- SA 570 Gr 70/60/SA and LTCS MOC- SA 387 GR 11. CL2).

For CS and LTCS pressure vessel as per client specification, plate required through thickness test as per SA 770 and determination of reduction of area as per SA 370. minimum reduction area not be less than 35%.

As per my understanding. for CS and LTCS plate material the mill produce the plate with ensure the steel cleanliness and minimum lamination and inclusion for comply the Minimum reduction area shall not be less than 35%


For High Alloy Material Plate like STAINLESS STEEL,DUPLEX STAINLESS STEEL, Incoloy 825,Inconel 625,which is used in the pressure Vessel. the through thickness test is not requested in the Plate requirement.

My query is why Through thickness testings is not required for High alloy plate material as compared with CS and LTCS plate materials.

I required metallurgist can answer my query in the ASME code point of view.

 

[DBreyer]

To answer your query Arulkumar P:

In higher alloyed steels the inclusions are not a problem.

MnS inclusions usually start globular in the steel. During rolling of the steel to form plate the inclusions get flattened out and can cover large areas in the steel.

Carbons steel get corroded in the wet H2S environment. As part of the corrosion reaction atomic hydrogen evolves. Some of it recombines to form hydrogen molecules. Another part of it moves into the steel and can recombine at inclusions in the steel (MnS) and form molecular hydrogen again -> creating blistering or act to initiate cracking in the steel (HIC).

Higher alloyed steels like austenitic stainless and duplex don't have the problem because they don't get corroded by the environment -> no Hydrogen evolution-> no hydrogen in the steel.

Additionally metallurgical composition is most often more tightly controlled in the higher alloyed steels -> less inclusions. hydrogen solubility is also higher and diffusivity less than carbon steels making them again less susceptible to the damage mechanism.
Other product forms like seamless pipe also suffer less from HIC as the inclusions don't get flattened as much during fabrication compared to plate.

 

[Arulkumar P]

Thank for your reply.

thank you sir.