RMT A500 Low Temperature Application

[caper656]

Recently had a request to replace a pressure vessel. It is made of RMT A-500 Gr B, relatively low pressure, welded end caps, non-code BUT specification sheet shows -20F MDMT. Now technically speaking, since its not code, there is no requirement for impact testing...or in addition, there is no additional customer request that the material be impact tested to a certain Joules. Therefore...technically...someone could supply an RMT A-500 GR B Pressure vessel that's noncoded and rated to -500F(exaggerated) with 0 Joules impact value? Since no code and no material code book references A-36/A500 as a impact tested material, theres no designation of Joules for an impact test that it has to meet. In addition, Im curious if its even practical to list MDMT on a material that has no code designation. Even if I listed +20F on a nameplate/Spec Sheet, I would think it would need "MDMT: +20F with 89ft/lb Impact Testing" or some disclaimer. That of course is considering how you correlate Impact test results with yield strength reduction

This is more of an exercise of industry understanding.

 

[david339933]

ASME Sec VIII Div. 1 - Allows an exemption for P1 materials (SA-36) to -20f, without impact testing....which is where your MDMT probably originated.

 

there is no additional customer request that the material be impact tested to a certain Joules

Careful here - client specification or lack thereof does not absolve you from meeting all minimum Code requirements. MDMT (among other factors) drives material selection, not the other way round; MDMT is determined by service conditions including geography if located outdoors.


"Everyone is entitled to their own opinions, but they are not entitled to their own facts."

 

[caper656]

Hello david, thanks for the reply. So I do see QW/QB-422's listing of A36 and A500 as a P1 material. If its accurate to correlate them as P1 falling under UG-20F, then I could see the exemption once the UCS-66 curve is determined. Can you confirm you agree on that? That said, referencing UCS-66 curves, my understanding is A-500 structural steel would fall under Curve A (a) as a structural shape. If you are assuming it falls under Curve B (c) , then i could see A-500 seen as tubing being used as the tube/plugsheet/wrapper....what are your thoughts? My previous general understanding was the A-36/A-500 structure shapes were not considered an ASME Code accepted "pressure vessel material" and therefore you couldnt apply UCS-66 or UG-20F

FIG. UCS-66 IMPACT TEST EXEMPTION CURVES (CONT’D)
NOTES:
(1) Curve A applies to:
(a) all carbon and all low alloy steel plates, structural shapes, and bars not listed in Curves B, C, and D below;
(b) SA-216 Grades WCB and WCC if normalized and tempered or water-quenched and tempered; SA-217 Grade WC6 if normalized and
tempered or water-quenched and tempered.
(2) Curve B applies to:
(a) SA-216 Grade WCA if normalized and tempered or water-quenched and tempered
SA-216 Grades WCB and WCC for thicknesses not exceeding 2 in. (50 mm), if produced to fine grain practice and water-quenched and
tempered
SA-217 Grade WC9 if normalized and tempered
SA-285 Grades A and B
SA-414 Grade A
SA-515 Grade 60
SA-516 Grades 65 and 70 if not normalized
SA-612 if not normalized
SA-662 Grade B if not normalized
SA/EN 10028-2 Grades P235GH, P265GH, and P295GH as rolled;
SA/AS 1548 Grades PT430NR and PT460NR
(b) except for cast steels, all materials of Curve A if produced to fine grain practice and normalized which are not listed in Curves C and D below;
(c) all pipe, fittings, forgings and tubing not listed for Curves C and D below;
(d) parts permitted under UG-11 shall be included in Curve B even when fabricated from plate that otherwise would be assigned to a
different curve.
(3) Curve C applies to:
(a) SA-182 Grades F21 and F22 if normalized and tempered
SA-302 Grades C and D
SA-336 F21 and F22 if normalized and tempered, or liquid quenched and tempered
SA-387 Grades 21 and 22 if normalized and tempered, or liquid quenched and tempered
SA-516 Grades 55 and 60 if not normalized
SA-533 Grades B and C
SA-662 Grade A;
(b) all materials listed in 2(a) and 2(c) for Curve B if produced to fine grain practice and normalized, normalized and tempered, or liquid
quenched and tempered as permitted in the material specification, and not listed for Curve D below.

https://files.engineering.com/getfi...-d330-4dd2-bf04-1640d503cdfe&file=Capture.PNG

 

[caper656]

ironic metallurgist: agreed! however, in my industry, the material is selected by the customer's metallurgist and it would be my duty to Impact test it unless except under ASME. However, for this unit, it was a lease unit thats staged as a "stock" item, that just so happened to land in Texas. So they rate them to -20F just incase. Also keep in mind, this is not an ASME coded pressure vessel unless you are saying the mere mention of MDMT is a code related term and therefore it would have to be validated by code requirements and that non-code pressure vessels shouldnt have any MDMT listing at all.

 

[metengr]

In addition, Im curious if its even practical to list MDMT on a material that has no code designation. Even if I listed +20F on a nameplate/Spec Sheet, I would think it would need "MDMT: +20F with 89ft/lb Impact Testing" or some disclaimer.

This is dependent on the service conditions of the vessel, and risk of brittle fracture in service.

 

[caper656]

Metengr, industry standard is to use RMT for water jacket sections....low pressure, typically under 50psi. This one is 10PSI, Engine Water Jacket

 

[david339933]

Correct. A500 C is not an acceptable material for pressure vessel use(UCS-23). SA-36 is however with limitations. See UCS-6(b).
Curve A is correct as well.

 

[caper656]

So it is safe to correlate A-500 gr B as A-36 for the Section II part D values? This is currently how our industry looks at it but ive never seen anything that correlates it this way besides its chemical makeup. If this is correct then I follow your logic and then we can apply curve A and UG-20F would then state "a) 1⁄2 in. (13 mm) for materials listed in Curve A of Fig. UCS-66."

That said....what is your opinion on why we cannot use Curve B's (c) listed below since technically A500 is Tubing? The current industry standard is that it falls under Curve B but I am not so sure.

(2) Curve B applies to:
(a) SA-216 Grade WCA if normalized and tempered or water-quenched and tempered
SA-216 Grades WCB and WCC for thicknesses not exceeding 2 in. (50 mm), if produced to fine grain practice and water-quenched and
tempered
SA-217 Grade WC9 if normalized and tempered
SA-285 Grades A and B
SA-414 Grade A
SA-515 Grade 60
SA-516 Grades 65 and 70 if not normalized
SA-612 if not normalized
SA-662 Grade B if not normalized
SA/EN 10028-2 Grades P235GH, P265GH, and P295GH as rolled;
SA/AS 1548 Grades PT430NR and PT460NR
(b) except for cast steels, all materials of Curve A if produced to fine grain practice and normalized which are not listed in Curves C and D below;
[highlight Yellow](c) all pipe, fittings, forgings and tubing not listed for Curves C and D below;[/highlight]
(d) parts permitted under UG-11 shall be included in Curve B even when fabricated from plate that otherwise would be assigned to a
different curve.

 

[david339933]

A500 is not an acceptable material, therefore it does not fall under any curve. SA-36 is Curve A. You may be able to certify material under UG-10.
What exactly are you attempting to do?

 

[caper656]

Use A-500 RMT with welded on A516 gr 70 End Plates to form a pressure vessel header for a heat exchanger. Since 1950, people have been using A-500 for Non-code headers with a -20F MDMT. im trying to understand how this is possible without impact testing...that said, there are no A-500 designated impact testing criteria...therefore...I can impact test all day and the values whether it be 0 or 11 ft/lbs is technically fine since there is no criteria...

A-500 is a p1 material though...and so under UG-20F, it states P1 is exempt per the governing thickness under the curves per USC-66.... so why cant we claim curve A or B?

 

Why not upgrade from SA-36, a pretty marginal PV material, to SA-516 Gr70? There's little if any cost difference, and normalized Gr. 70 will likely cover all your needs.

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."

 

[weldstan]

Whereas A500 is not a material listed in ASME II for vessels constructed per ASME VIII, why are you concerned when your vessel is not made to ASME VIII? If the vessel will not experience a metal temperature of -20F or even remotely near it during its pressurized service, why are you concerned? If the vessel is operating with stresses very low compared to its specified minimum yield strength, again why be concerned? You seem to want to cherry pick parts of ASME VIII to suit your materials selection and your vessels integrity.

If you have high stresses induced during service at low temperatures (below 32 F), A500 should not be used. Absorbed energy at 0 F in a Charpy test will most likely be less than 5 ft-lbs.

 

[caper656]

Ironic: Although material wise there is some cost increase, welding and manufacturing will be dramatically increased for a SA-516 plate box. Welding, handling, how its constructed. RMT can be drilled and tapped in one pass in 20-40ft sticks then cut to the proper length, end plates welded on. Vs ordering beveled SA-516 gr 70 plate, weld prep, subarc/flex pass,etc. Due to this being an Engine Jacket, all namebrand manufacturers utilize A-500 gr B for low pressure, non-lethal service water jackets to cool compressor systems.

Weldstan: The key to your question is that the Job requirement calls for replacement A-500 Header Box nameplated with the original MDMT of -20F.(it is a leased compressor package that could be moved anywhere that experiences down to -20F per the original build). Although 100% typical of the industry, my concern is that since the original A500 build is not a ASME II material nor ASME Stamped, it has no formal validation or exemption to insure its good to -20F. With no criteria, technical, I can impact test it to -20F and result in 5 ft-lbs and that would satisfy the job requirement for testing. It doesnt meet or not meet any ASME Sec II criteria or secondary criteria. Does that make sense? In contrast, if I needed to test SA -516 Gr 70 to -58F, then ASME dictates the impact energy that it must absorb via Charpy Impact Test before it can be approved.

 

[david339933]

Sec. VIII has it's own impact energy values based on min. specified yield strength of the material. If A500 Gr. B was hypothetically an approved material it would require 15 ft-lb. (Fig. UG-84.1)

 

[caper656]

Thanks David. This matches my logic...one additional item I found was under asme sec ii for art under table 1, it list a500 as an appurtenant material to a36. Therefore, yes it would need to meet 15ft/lb under 1inch thick unless exempt per ucs-6 or ug-20f which states p1 material under 1/2in for curve a and 1in for curve b. I would say a36 would be classified as curve a and tubing under B part c for tubing. That said, I don't even think RMT a500 is made thicker than 1/2"

 

[weldstan]

While the original manufacturer stated that the equipment was good to operate at -20F, you may not be able to so do because you appear to not know all of the original manufacturer's design constraints. It all depends on the stresses induced in the A500 material especially at the welds where flaws are most likely. If stresses are sufficiently low as a percent of yield strength, you should be able to guarantee operation at -20 F ambient temperatures with appropriate volumetric weld inspections.

 

[r6155]

I recommend fine austenitic grain size materials for -20F

Regards

 

[SnTMan]

Fact is there are a number of ways under Sec VIII, Div 1 to get any old CS to -20 F.

Don't worry about it, get on with life.

Regards,

Mike


The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[david339933]

Ha!...and Mike for the win.