may SA-36 be used to MDMT -50C as tie rods? 2

[YuJie_PV]

hi all,

i've a question regarding to UCS-66 in ASME VIII-1:

it's a heat exchanger constructed to ASME VIII-1 with MDMT -50C.
may i use SA-36 for the tie rods in tube bundle?
per my experience, SA-36 is not suitable for such cold temperature, but i find the following paragraph:

UCS-(b)(3) When the minimum design metal temperature is colder than −55°F (−48°C) and no colder than −155°F(−105°C), and the coincident ratio defined in Figure UCS-66.1 (Figure UCS-66.1M) is less than or equal to 0.35, impact testing is not required.

per my understanding, in case sa-36 subject to quite small stress, it can be used to a MDMT as cold as -50C.
moreover, if SA-36 is suitable for such temperature as pressure-containing component, why not for tie rods in such MDMT?
the idea seems conflicting to common sense. am i missing something?

Appreciate any comments.

Thanks in advance.

 

[CuMo]

Why not use SA-320 L7 bolting material instead? Cheap, easy to get in variety of diameters and the MDMT is -50 deg C.

https://www.wermac.org/bolts/a193-b7_a320lL7_studs.html

Unless you have a practical reason to use SA-36 which I believe is structural steel - the option above seems better to me.

You might want to look into TEMA RCB-4.7 and RCB-1.1.4 although when materials are concerned TEMA relies on the ASME code.

Threaded only tie rods are neither pressure nor welded component so the MDMT requirements wouldn't typically apply.

However if you are expecting some loads (vertical exchanger where the baffles weight is hanging on the tie rods) or vibrations - you might want to pick a more ductile material just in case.

 

[YuJie_PV]

@CuMo. thanks for advice.
i've already given up the option of SA-36 for MOC of my tie rods
but out of curiosity, i am still confused with UCS-66(b)(3) in ASME VIII-1.
let's say, there is a vessel with atmospheric pressure and mandated to be constructed to ASME VIII-1, MDMT is -50C.
may i select MOC of SA-36 for the shell of the vessel based on UCS-66(b)(3)?
here is my philosophy that the coincident ratio in the shell should definitely be less than 0.35, thus SA-36 seems acceptable in such design condition per ASME VIII-1.
is my understanding correct?
thanks

 

[CuMo]

Section UCS-66 works only with the ASME materials which are listed in Figure UCS-66 and Table UCS-66.
If you can't find your SA-36 in there (I think you won't be able to find it) - you are looking for trouble.
I suggest you leave this SA-36 alone. Not sure who is giving you such ideas
Look also into ASME VIII-1 Appendix 19, section 19-3 Materials.
You'll find your answer there too.

 

[david339933]

SA-36 is an approved material. See UCS-6 and note 1 of table Fig. UCS-66. That being said, it should only be used for the "Farm Code".

 

[jt1234]

YuJie your assessment is correct that if no loading, it can go down to -155F in pure static condition. We use UCS-66 to figure out the minimum metal temperature without impact testing for auto-refrigeration condition when pressure starts falling in ethylene plant. The point is, if you have sudden shock load or vibration that you can not figure it out to calculate the ratio, the tie rod can be too brittle at low temp.

 

[YuJie_PV]

CuMo, David, and Jt1234, thanks for all the comments.

let me explain why i have such inquiry. my job is reviewing drawing submitted by manufacturers in behalf of owner. when i give comments to revise something in the drawing, i often need to be ready to give sufficient basis.

let me imagine such a scenario, manufacturer select MOC of SA-36 (or sa-283) for a vessel as stated in my previous post above, and quoting UCS-66(b)(3) to justify their selection. how shall i reject such design if both my datasheet and owner specification never address such condition?

Thanks in advance.

 

[jt1234]

Your comments on dwg will be: tie rod can suffer unpredictable shock loads, vibration, bending and tensional load under tightening, such that tie rod can crack under load at low temperature and hence not recommended.

 

[YuJie_PV]

@jt1234, sorry.
i've not made myself clear,it's not about tie rods.

let me rephrase. it is hypothetical issue.
say it's a vessel with design pressure: atmospheric (ASME VIII-1 is mandatory even the pressure is atmospheric), MDMT is -50C
manufacturer select SA-36 (or maybe SA-283 ) to construct the shell of the vessel. when the GA drawing is submitted to me, i definitely raise my concern to MOC of shell. i ask vendor to use MOC with better toughness.
let's say the manufacturer insist his design and quoting UCS-66(b)(3)to justify the MOC.
how shall i reject then? let's say it's a regular vessel subjected to no shock or vibration.

Thanks

 

[jt1234]

Per code, you can not reject it. It is personal preference to use better material, but you can not technically justify it. You will only pay more for it or a change order.

 

[YuJie_PV]

@jt1234,thanks for your comments.
i used to believe that ASME Code is almost perfect, if not totally.
when i find something conflicting to my experience or common practice, i always believe there must be something hidden in the code that i've not found.

i've been confused on the topic for some time.
ASME code seems quite aggressive on the determination of MDMT based on your comments.
maybe there is nobody able to clarify the issue in the forum.
i'll keep eye on the topic in the future.
you refresh my original thought, thanks.

Regards

 

[GD2]

OP,
I don't see a reason why you can't use SA-36 as tie rods for the HX to MDMT -50C. It's a non-pressure part (internal part). To do a due diligence, just check if the material is listed and do a quick calculation for fer stress ratio. There will be some tensile stress on the tie-rod (with no vibration load as you assumed).

GDD
Canada

 

[SnTMan]

On the face of it, I'd agree with the various posts that SA-36 is acceptable for tie rods at the -50C MDMT. Stress in the tie rod should be negligable. After all, use of non-spec (commercial grade) materials for bundle cage materials is common.

Broader question for the OP: What are you using for spacer tubing, baffles, skid / seal bars etc? Any MDMT concerns there?

Regards,

Mike

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

 

[georgeverghese]

Tie rods will need to withstand flow induced tube bundle vibrations, so it needs to be ductile enough at the min operating temp to deal with the transient stresses induced by vibration. This is obviously not a process safety concern in itself, but tie rod failure could lead to bundle vibrations which may then lead to tube ruptures at the tube to tubesheet joints.

 

[YuJie_PV]

thanks for all replies.
@SnTMan,

at first, i'd like to use carbon steels like SA-36 for these non-pressure retaining parts in tube bundle, because the fluid in shell side is non-corrosive. now i turn to Austenitic Stainless steel, same as the MOC of tube.

Regards.

 

[r6155]

SS 304 rods for fixed tubesheets.
Regards