Are there any differences in the manufacture of CLASS 1 and 2 in ASME VIII-2?
Is there a difference between the manufacture of CLASS 1 and 2 of ASME VIII-2?
Table of Contents
The other day, a former coworker of a colleague, through a coworker, asked me about ASME Ⅷ-2.
Q: Are class 1 and class 2 NDEs for ASME Ⅷ-2 the same?
A: Yes, it is the same. Manufacturing and inspection are no longer differentiated by class 1 and class 2.
Re-question: VIII-2 volume design, class 1, and class 2 design concept is not the same, class 2 material allowable stress to be taken than class 1 to be higher, according to reason is not to be higher non-destructive requirements? What is the deep-seated reason here?
A: It should be said that according to the lower allowable stress, the non-destructive requirements are not further reduced because class 1 and class 2 are later divided out (to add class 1 is new, now class 2 is equivalent to the original).
Those new to ASME Ⅷ-2 may not understand the implementation level of class 1 and class 2, especially welding and inspection engineers.
This is because ASME Ⅷ-2 is a confusing part of the system that has not yet been fully developed. Instead, it was rushed into class 1 and class 2, and it was announced that class 1 would replace ASME Ⅷ-1 in the future.
ASME Ⅷ-2 was originally based on EN13445, and the 2007-2015 editions of ASME Ⅷ-2 did not distinguish between class 1 and class 2, and the safety factor for tensile strength was 2.4 (the same as the European standard).
In the 2017 edition, class 1 and class 2 were introduced, but there is only one more class, one more set of tensile safety factors, and only the ratio of low-stress impact-free has been divided into 0.3 and 0.24. There is no distinction in the impact energy value of the material (27J and 24/22J may be more appropriate). There is no further distinction in the manufacturing requirements (the actual manufacturing parts of ASME Ⅷ-1 and Ⅷ-2 are also very different), and the manufacturing requirements of the head are not differentiated. There is no further distinction in the manufacturing requirements (the actual ASME VIII-1 and VIII-2 manufacturing sections differ very little), no distinction in the calculation of the deformation rate of the head, and no distinction in the NDT requirements; it is all the same, and it can be said that it is being implemented according to the stricter (tensile factor of safety is 2.4) requirements. Will it be changed or not? I don’t know.
There is no increase in the types of materials, but note that ASME Ⅷ-2 can use a lot fewer materials than ASME Ⅷ-1 (commonly used materials SA-179 and S32750 are not available, and S32750 can only be used in ASME Ⅷ-2 using a code case).
Even the permissible stress of class 1 is still to be rigorously (perhaps there is an internal dispute); according to Volume II, Part D, the list of the permissible stress of class 1 is only low stress, and the principle of the Appendix is also to be divided into high and low stresses is not uniform.
By the permitted stress talk about swaying left and right.
Whether it is work or life, the most taboo is to sway from side to side.
ASME Ⅷ-2 Class 1 equipment of the permissible stress issue; maybe the ASME organizing committee of the internal sway wants to ASME Ⅷ-1 to reduce the safety factor, but also want to and ASME Ⅷ-2 Class 2 relative consistency. The swaying has caused a bit of a mess, and the current allowable stress table has deviated from its original intent. The introduction of ASME Ⅷ-2 Class 1 will replace ASME Ⅷ-1 in the future and compete with EN 13445 for dominance in the international arena, not to say win, at least not to be pulled far away.
In ASME II, Volume D, Appendix 2, Table 2-100, it is clear that the permissible stress of austenitic stainless steel and other materials are also divided into high and low stress. However, in the actual allowable stress table (Table 2A,2B), there is only one row for allowable stress, and there is no high stress. The actual allowable stresses in Table 2A contradict those in Table 2-100 in Appendix 2.
Equipment for ASME Ⅷ-2 Class 1
ASME Ⅷ-2 Class 2 is standardized to EN 13445, and much of the content is copied directly from EN 13445. Understandably, there is no use of high and low stresses because the permissible stresses of austenitic stainless steels, etc., are high, and there is no need to divide them into high and low stresses. The principle of permissible stresses for CLASS 2 equipment differs from other parts, so there is no problem copying directly from EN 13445.
ASME Ⅷ-2 Class 2 equipment
ASME Ⅷ-1 Equipment
Class 1 equipment is proposed to enhance competitiveness, reduce the thickness of but currently engaged in the austenitic phase (mainly austenitic stainless steel, nickel-based alloys, copper alloys) material permissible stress not only did not improve but also reduced, how to increase competitiveness.
This permissible stress is only a personal understanding of the issue; the reason for the inconsistency of the consultation has yet to be replied to!
ASME Ⅷ-2 CLASS 1 and CLASS 2: A simple comparison.
ASME to fight against EN13445, 2007 completely by the EN13445 set of rewrite ASME Ⅷ-2, but due to new ideas and RPE and other reasons ASME Ⅷ-2 promotion is not favorable, in 2017 to further modify the ASME Ⅷ-2 design of the equipment is divided into two categories of CLASS 1 and CLASS 2; CLASS 1 can be regarded as a future replace ASME Ⅷ-1 equipment only with a lower margin of safety; CLASS 1 equipment is for the most part not subject to RPE review. This saves design cycles and design costs and reduces equipment costs relative to ASME VIII-1 low-temperature carbon steel and low-alloy steel equipment.
The following briefly compares the two vessel classes in terms of applying the standard in seven areas.
1. Allowable stress:
CLASS 1 of the simple min (tensile strength/3.0, yield strength/1.5); (see Ⅱ D Appendix 2)
CLASS 2 of the simple min (tensile strength/2.4, yield strength/1.5); (see Ⅱ D Appendix 10)
The permissible stresses for CLASS 1 packaging are listed in Table 2A or 2B of Volume II, Part D. (ANNEX 1-B 1-B.2.9)
CLASS 2 Allowable stresses for packaging are given in Table 5A or 5B of Volume II, Part D (ANNEX 1-B 1-B.2.10).
2. A Manufacturer’s Design Report (MDR), i.e., reviewed by a Registered Professional Engineer (RPE) (184.108.40.206):
CLASS 1 is required for fatigue analysis design only or when design rules are not given per Chapter 4, and calculations are analyzed per Chapter 5. RPE review is not required for full design by rule.
CLASS 2 is required for RPE.
3. Scope (design by rule) – 220.127.116.11
CLASS 1 When design rules are not given in Chapter 4, analyze and design in Chapter 5 or when the AI accepts the rules-based design methods of other codes.
Chapter 5 analytical design is separate from the design rules mandated in Chapter 4.
CLASS 2 When design rules are not provided, the manufacturer shall perform a stress analysis by Chapter V, considering all UDS-specified loads.
Chapter 5 analytical design may establish the design thickness and or structural shape of the vessel (e.g., open hole reinforcement structure for receivers) instead of the Chapter 4 design rules.
4. Design thickness – 18.104.22.168
CLASS 1 The design rules of Chapter 4 apply to the loads and combinations of load conditions specified in 22.214.171.124 unless no design rules are provided in Chapter 4.
CLASS 2 may be designed using the rules in Chapter 4; additionally, the design thickness may be designed analytically using Chapter 5, even if the design thickness of the analytical design is less than the design thickness designed by the rules in Chapter 4.
5. Chapter V may only be used with CLASS 2 or CLASS 1 for fatigue packaging. -126.96.36.199.1.
6. Manufacturing inspection tests are separate from CLASS 1 and CLASS 2.
7. User Design Technical Conditions (UDS) – 2.2.1
CLASS 1: RPE signature is not required under normal circumstances. However, UDS that require fatigue analysis must comply with Appendix 2-A and be signed by the RPE.
CLASS 2: UDS must be signed by RPE.
Note that the user’s UDS and the manufacturer’s MDR signed by the RPE cannot be the same person. The RPE signature review and signing costs range from 4000 to 7000 U.S. dollars, more than 7000; consider changing the person to inquire about it. If the manufacturer fully prepares the user’s UDS, basically, there is no need for the RPE to increase the content of the price is cheaper than the review of the drawings.
As ordinary front-line technicians, we focus on applying standards!