ASME Section VIII Div 2 Class 1 & 2 ( 2017 ) 5

[abdelkarim10]

Hello
Can any one tell the difference between new Class 1 & 2 in ASME Section VIII Div2 (2017 )
Thanks

 

[TGS4]

Yes - I am very familiar with the difference. It is best summarized as follows:

Class 1
Design margin against ultimate - 3.0
Design margin against yield - 1.5
Professional Engineer required to certify the UDS - no (unless fatigue analysis is required)
Professional Engineering required to certify the MDR - no (unless fatigue analysis is required)
Can Part 5 be used to supersede the design rules in Part 4 - no
Maximum ratio of membrane stress to yield during hydrostatic test - 0.9

Class 2
Design margin against ultimate - 2.4
Design margin against yield - 1.5
Professional Engineer required to certify the UDS - yes
Professional Engineering required to certify the MDR - yes
Can Part 5 be used to supersede the design rules in Part 4 - yes
Maximum ratio of membrane stress to yield during hydrostatic test - 0.95

There are several other aspects, but those are the major ones.

 

[marty007]

Has anyone been seeing much interest from customers yet for going with VIII-2 Class 1 vs. VIII-1?

 

[MrPDes]

In Europe not allot of fabricators have Div 2 Certification.
FEA not being allowed on Class 1 vessels does restrict its use to the most basic vessels. It would be good if a class 1 vessel that requires an element of FEA could use Part 5 design method using Div 1 allowable stresses (3.4 margin against UTS).

 

[TGS4]

The only restriction on Part 5 for Class 1 vessels is that it can't be used to overrule otherwise existing rules in Part 4. If there is a perception that FEA is not permitted for Class 1 vessels, that is incorrect. All use of FEA for Class 1 uses the Class 1 allowable stress basis.

There is a Code Case that permits Division 1 fabricators to build Class 1 vessels. Uptake by fabricators should be much more, but incorrect assumptions or perceptions are stymying the effort.

 

[oknow]

TGS4,

Thanks for the information. Hope all is well in HO.

All,

ASME has a new policy oh how a ASME Section VIII Div.1 can obtain a Section VIII Div. 2, Class 1 permission to Construct under certain conditions..

https://www.asme.org/

http://wwwasmeorg/media/ResourceFil...tification/BPV-FRM-11-U2-ClassApplication.pdf

This Guide is prepared for the use of a ‘U’ Certificate Holder interested in obtaining a “U2 Class 1” Certificate under the provisions of Section VIII, Div. 2 Code Case 2891. It is not intended to replace or interpret the requirements of Section VIII, Div. 2 of the ASME Boiler and Pressure Vessel Code for the Construction of Class 1 pressure vessels. It is intended to assist the Certificate Holder in evaluating its Quality Control Manual to ensure the requirements to construct Section VIII, Div. 2 Class 1 pressure vessels are incorporated successfully. Section VIII, Div. 2 Class 1 pressure vessels are defined in ANNEX 1-B DEFINITIONS, clause 1-B.2.9 of the 2017 Edition of Section VIII, Div. 2.

https://www.asme.org/

http://wwwasmeorg/media/ResourceFil...0-U2-Class1-CertHolderQC-Manual-CHECKLIST.pdf

 

[MrPDes]

Thanks for the clarification,

From section 2.3.3.1(a) it specifies that the manufacturers design report only needs to be certified for a Class 1 vessel if it incorporates fatigue or Part 5, so essentially a Class 1 vessel with fatigue or FEA essentially has to jump through all the same certification hoops as a Div 2 2015 vessel or Div 2 2017 Class 2 vessel, however Class 1 has more conservative design margins.

I assume the only time Class 1 with fatigue or FEA would be used, is when a manufacturer has only acquired a U certificate for Div 2 Class 1 (and not class 2).

 

[tigny]

Dear all,

when designing and constructing a vessel according to the methods of ASME.BPVC.VIII.1 (without U-Stamp), if required to use U-2(g) because of geometry not dealt with by this Code, we would go to ASME.VIII.2 §5 Design By Analysis. All that can be design according Design by Formula (UG, ...) is respected.

We would base the calculation on the ASME.II.D Table 1A or 1B allowable stresses, sometimes with casting coefficient added (S=0,8*S) as a basis of material characteristics for a limit load model, where the yield strength defining the plastic limit is 1.5 times the allowable stress, therefore 1,5*0,8*S (use of an Elastic-Prefectly Plastic material model).
Is it compatible with the new DIV. 2 CLASS 1 classification?

Since allowable stress in ASME.II.D Table 1A or 1B are based on S[sub]T[/sub]/3,5, isn't there a discrepancy with the design margin against ultimate strength of 3,0?
Are the factored combinations in TABLE 5.4 or TABLE 5.5 of DIV. 2 OK for this case?

tigny

 

[TGS4]

For Table 5.4 work (Limit Load), your approach is appropriate for using the VIII-1 value of S to define the plastic limit. The load factors are then appropriate.

For Table 5.5 work (Elastic-Plastic), use Beta=3.5.

 

[OnG_Engr]

All,

Per Part 2.3.3.1 (a), the MDR only needs certification if fatigue analysis is performed and/or analysis from Part 5 is used (e.g. for a nozzle).

Per Part 2.2.1.1, the UDS only needs certification if fatigue analysis is performed. HOWEVER, the User doesn't need certification if the Manufacturer uses analysis from Part 5.

 

[TGS4]

OnG_Engr just to clarify your item on the MDR certification, the Code says:

2.3.3.1 (a) Class 1. The Manufacturer’s Design Report shall be certified in accordance with Annex 2-B when either of the following are performed:

(1) fatigue analysis​

(2) use of Part 5 to determine thickness of pressure parts when design rules are not provided in Part 4​

(b) Class 2. The Manufacturer’s Design Report shall be certified in accordance with Annex 2-B.

So, my perspective is that nozzle analysis per Part 5 would not necessarily require certification of the entire MDR. Rather, if you are determining the thickness of the component, then the certification is required. However, if you are confirming that a thickness selected from Part 4 (pressure thickness) is suitable for supplemental loads not specifically covered by Part 4, then certification per 2.3.3.1 (a)(2) would not be activated.

 

[Trestala]

2.3.3.1 (a) Class 1. The Manufacturer’s Design Report shall be certified in accordance with Annex 2-B when either of the following are performed:
(1) fatigue analysis
(2) use of Part 5 to determine thickness of pressure parts when design rules are not provided in Part 4

If my understanding is correct, the wording is very clear that Div. 2 Class I vessels can't have any cyclic loading, but please still allow me to ask: If we have a floating production project where there is constant ship motion which we need to evaluate for fatigue (not exempted from Part 5.5.2 screening), and the client requires compliance to ASME BPVC Sec. VIII (unstamped), we can't shift to Div. 2 Class I from Div. 1 even if Part 4 thicknesses would still govern? I would expect Owners and EPC contractors to entertain the idea to shift to Div. 2 Class I for FPSO projects for the weight savings. I guess the wording is clear and the lower design margin would not allow it?

 

[TGS4]

RaymondN, your understanding is completely incorrect. Div 2 Class 1 absolutely permits design for cyclic service. The only caveat is that the UDS then requires certification, as does the MDR.

 

[MrPDes]

RaymondN,
The wording says that it can be Class 1 if there is fatigue. However, the design report has to jump through all of the same hoops as a Class 2 vessel (Independent Engineer design review etc). Therefore a Class 1 vessel with fatigue is essentially a Class 2 vessel with conservative allowable stresses.

I assume by Section VIII (Unstamped) you mean Div 1? (In general accordance with ASME VIII Div 1)

 

[Trestala]

Sorry I left out what I actually meant to ask which is if we can have a Div.2 Class 1 vessel with fatigue WITHOUT certification even if Part 4 thicknesses governs and Part 5.5 was only used for verification. And even if stamping is not required.

 

[TGS4]

If stamping is not "required", then frankly you can do whatever you want.

If you're going to follow the rules, then if you "need" a fatigue analysis, i.e. You cannot pass a fatigue screening assessment, then certification of the UDS and MDR are mandatory.

The typical approach would be to have the user define the cycles when writing the UDS. Then, the User (or their designated agent) would perform the fatigue screening assessment in order to ascertain whether a fatigue analysis is required. If it is required - certification is mandatory; our it is not - certification is optional.

 

[Trestala]

Thank you TGS4 and MrPDes for clarifying. That answers my question.

 

[MrPDes]

RaynondN,

From you comments here and in another current thread that you have started it appears you are using the WRC 497 parametric investigation of large idealized nozzles "without reinforcing pads" with applied loads to design a nozzle which has a reinforcing pad and additionally experiences fatigue service. This design has failed with Div 1 allowable stresses, therefore you are trying with reduced div 2 allowable stresses. The design won't be code stamped or even independently reviewed.

Is this correct? Could you confirm that this equipment will be a long way from land, far away out to sea?

 

[Trestala]

Using Div. 2 Class 1 is a theoretical scenario I am curious for offshore (FPSO) installations where weight is managed very tightly.

The WRC 497 case on the other thread is onshore and no cyclic loading, and is designed for ASME VIII, Div. 1, 2015 Ed.