ASTM A455 Vs A516gr70 1

[CSGWB]

I am currently looking at an air treatment vessel built in 1999 from ASTM A455 material. I have not come across this material before. What benefits does it have over the normal PV material ASTM A516 Gr70.

I do note that A455 has a higher carbon content (0.33 vs 0.2), what effect does this have?

This vessel has a heavily corroded bottom head which needs replacing, is there any metalurgical issue in replacing this with A516Gr70?

Regards

CSGWB

 

[metengr]

The material of the vessel, if it is built to ASME Section VIII, Div 1, is most probably ASME SA-455, "Specification for Pressure Vessel Plates, Carbon Steel, High-Strength Manganese". The maximum plate thickness furnished under this specification is 3/4". If the original vessel head material was corroded from moisture and oil, etc that settled out in the bottom of the vessel, this repair is feasible - replace the corroded section and install a flush patch plate that is full penetration welded to the original shell material, or depending on the size of the head, manufacture a replacement head and re-weld to the vessel.

Regarding the pressure vessel repair. First off, if this is a pressure vessel that is regulated by the Jurisdiction where it is installed, the repair should be performed in accordance with the National Board Inspection Code (NBIC), and by an organization that has a valid National Board R- certificate to Repair/Alter Pressure Retaining items.


The plate material for the repair should be similar in chemical composition and either meet or exceed the strength properties of the original material used for the vessel. In this case, you should evaluate the allowable stresses for the original material and compare with the allowable stress of the material used for the repair (SA-516 Gr 70) at the maximum design service temperature (which you did not provide).

If the allowable stresses are comparable, you are permitted to use the SA-516 Grade 70. Nondestructive testing (NDT) requirements for this repair shall be performed in accordance with the NDT requirements in the original code of construction (ASME Section VIII< Div 1).

 

[metengr]

I checked the allowable stress values for SA-455 and for SA-516 Gr 70 up to 400 deg F. The SA-455 plate material has a reported allowable stress of 20.9 Ksi, where SA-516 Grade 70 has a reported allowable stress of 20.0 Ksi.

For this vessel repair, the SA-516 Grade 70 could be used. However, what I would do, is fabricate the entire lower head of the SA-516 Grade 70 and increase the thickness in proportion to match the slightly higher allowable stress value of the SA-455 vessel material.

 

[deanc]

Careful: Some Manufactuers have used the higher stress value of SA-455 to avoid repads. So consider this.

SA-455 can be the made from same heat as SA-516 but the heat treatment is different.

There are also some corrosion advantages.

 

[metengr]

Just to clarify a bit to the response by deanc. The SA-455 plate material is a higher carbon version of SA-516 Grade 70, which increases strength properties in comparison to other carbon steel plate materials. Carbon provides a significant impact on strength properties of carbon steel plates - the higher the carbon content, the higher the strength.

Regarding heat treatment, the SA-455 plate is normally furnished in the hot rolled condition - this is not the same as a normalization heat treatment condition. If the purchaser needs otherwise, the plates can be applied in a normalized and tempered condition.

For SA-516 Grade 70, the carbon content is slightly lower in comparison to the SA-455, which would result in lower strength for comparable heat treatment conditions. The SA-516 plates are normally supplied in a hot rolled condition. Their normal use is for applications where notch toughness is as important as strength. In this case, the SA-516 plates are supplied with a normalization heat treatment to assure minimum toughness properties.

The last comment – both plates, the SA-455 and the SA-516 Grade 70 would exhibit very similar corrosion resistance in this type of environment (air tank). The advantage with SA-516 Grade 70 is for hydrocarbon service environments, and it can be used at higher service temperatures in comparison to SA-455 (Section VIII limitation is 650 deg F).

 

[deanc]

metengr: I have no problem with any of your statements,I was not clear enough.

I have seen SA-455 and SA-516 Gr70 from the same mill,in the same heat,with the same thickness. The tensiles were different with the 455 being higher.

I have also seen several manufactuers take advantage of this to avoid repads and to allow higher pressures.

This could be the case for CSGWB esp.for an older air tank.

I am only saying that he should consider this. It was a "head scratcher" the first time I saw it---but it works.

 

[metengr]

yes, I agree.

 

[CSGWB]

Thank you Metengr and Deanc for your responses.

The head in question has suffered general corrosion so unfortunately does need to be removed and replaced. Code calculations have shown that A516-70 is acceptable at the nominated thickness and I have chosen to add a bit to take into account future corrosion regimes.

I would take it then that A455 material has a lower cost that A516-70 due to the hot rolled vs normallised condition?

Would it be the case of the A455 being slightly work hardened in the hot rolled condition, while the A516-70 has been stress relived through normalising?

Regards

CSGWB

 

[metengr]

CSGWB;
The SA-516 Grade 70 may not be in the normalized condition. In fact, if the thickness is less than 1/2" it would probably be supplied in a hot rolled condition unless you had specified a normalize and temper heat treatment.

To answer your last question

Would it be the case of the A455 being slightly work hardened in the hot rolled condition, while the A516-70 has been stress relived through normalizing?

No. Hot rolling is performed at a temperature that is typically at or above the lower critical transformation temperature, and would not work harden the steel.

The cost difference is strictly supply and demand of SA-455 versus SA-516 Grade 70 under similar heat treatment and strength requirements for end use.

 

[CSGWB]

OK - Thank you for your assistance Metengr.

CSGWB