ASME section VIII stands for “American Society Of Mechanical Engineers”.
ASME deals with the code of construction of the pressure vessels. It is a part of the ASME BPVC codes.
NEED OF ASME VIII CODE
ASME codes came into existence to avoid the accidents caused in the industries which took several lives and a huge loss to the industries.
ASME provided standard codes or the procedures which should be followed while the construction of the pressure vessels.
ASME section VIII is further divided into 3 parts:
The best form to understand them in detail is in the form of the table given below:
|SECTION VIII DIVISION I||SECTION VIII DIVISION II||SECTION VIII DIVISION III|
|SR.NO||Division I is made for only Unfired” Pressure Vessel Rules.||Division II is made for Alternative rules for a high-pressure vessel than those used in Division I||Division III contains Alternative rules for higher pressure vessel|
|1||Pressure Limits||Normally up to 3000 psig||Pressure Limit is usually 600+ psig||It has No limits, Normally it starts from 10,000 psig and above.|
|2||Experimental stress Analysis||Normally not required||May be required||Experimental design verification is required but may be exempted.|
|3||User||User or designated agent to provide specifications.||User’s Design Specification with detailed design requirements includes AD 160 for fatigue evaluation.||User’s Design specification with more specific details including contained fluid data, etc. with useful operation life expected and others. It is a Designer defined.|
|4||Manufacturer||Manufacturer to declare compliance in the data report||Manufacturer’s Design Report certifying design specification and code compliance in addition to a data report||Same as Division 2|
|5||Engineer’s Certification||IT is Normally not required in Division I.||Proficient Engineers’ Certification of User’s Design Specification just as Manufacturer’s Design report Professional Engineer will be knowledgeable about the pressure vessel plan.||Same as Division 2 however the Professional Engineer will be in high-pressure vessel structure and will not finish the paperwork for both User and Manufacturer.|
- This Code contains obligatory necessities, explicit denials, and non-required direction for pressure vessel materials, plan, manufacture, assessment, investigation, testing, and confirmation, and pressure relief.
- This code isn’t a handbook and can’t supplant training, experience, and utilization of engineering judgment. Utilization of engineering judgment ought not to be utilized to overrule the compulsory necessities of this code.
Utilization of Code:
- The Code is distributed at regular intervals now and gets compulsory following a half year of its production (For instance ASME SEC VIII DIV I distributed on July 1, 2017, gets required from Jan 1, 2018).
- This code isn’t a handbook and can’t supplant training, experience, and utilization of engineering judgment.
- Utilization of engineering judgment ought not to be utilized to overrule the compulsory necessities of this code.
The Body of ASME SEC VIII DIV I is made up of various subsections namely:
Subsection A: General Requirements
- Part UG: This part comprises general Requirements for the fabrication of pressure vessels by all methods and materials.
Subsection B: It consists of Requirements relating to the Methods of Fabrication of Pressure Vessels. It consists of various parts such as:
- Part UW: This part comprises of the details required for the manufacturing of the pressure vessel by welding.
- Part UF: This part comprises of the details required for the manufacturing of the pressure vessel by making use of forging.
- Part UB: This part comprises of the details required for the manufacturing of the pressure vessel by making use of Brazing methods.
Subsection C: Requirements About the Classes of Materials. The various parts of this subsection are:
- Part UCS: Requirements of Pressure Vessels Constructed of Carbon and Low combination Steel
- Part UNF: This part gives information about the Requirements of Non-ferrous pressure vessels.
- Part UHA: This part gives information about the Requirements of High Alloy Steel pressure vessels.
- Part UCI: Requirements of Pressure Vessels Constructed of Cast Iron.
- Part UCL: The guidelines in Part UCL are relevant to pressure vessels or
- on the other hand vessel parts that are developed of base material with erosion safe fundamental or
- weld metal overlay cladding and to vessels and vessel parts that are completely or in part fixed inside or outside with corrosion resistant plate, sheet, or strip, connected by welding to the base.
- plates previously or in the wake of shaping or to the shell, heads, and
- Part UCD: Requirements of Pressure Vessels of Cast Ductile Iron.
- Part UHT: Requirements of Pressure Vessels of Ferritic Steels with Tensile Properties Enhanced by Heat Treatment.
- Part ULW: Requirements of Pressure Vessels Fabricated by Layered Construction.
- Part ULT: Alternate guidelines for Pressure Vessels Constructed of Materials having Higher Allowable Stresses at Low Temperature.
- Part UHX: This part basic comprises of Rules for Heat Exchangers (Shell and Tube).
- Part UIG: Requirements of Pressure Vessels Constructed of Impregnated Graphite.
- Part UCD: Requirements of Pressure Vessels of Cast Ductile Iron.
Now we will discuss in detail about the subsection A:
UG 1: SCOPE
The prerequisites in this area are material to all pressure vessels and vessel parts and will be utilized together with the particular necessities as given in Sub Section B, C, and Mandatory Appendices.
UG 4: MATERIALS
- Materials for Pressure Parts Shall affirm to the prerequisites given in ASME SEC II Part D, subpart 1.
- Materials can be Dual Certified (For Example a plate can be guaranteed as SA 516 Gr 60 and SA 516 Gr 70 according to ASME SEC II PART A by factory gave the material meets all the prerequisites of the distinguished material determination or evaluations.
- No Pressure parts (Lugs, Skirts, and so forth… ) need not be distinguished however on the off chance that joined by welding will be of weldable quality.
- Materials other than those permitted by the standards of this division will not be utilized.
- Engineering judgment to be utilized by the producer to guarantee the client that the materials utilized for the development of pressure vessels will perform acceptably for the planned help.
- The material physical properties required by configuration will be taken from ASME SEC II Part D subpart 2.
- If the code doesn’t contain the properties’ esteems the maker may utilize other legitimate hotspots for the required data.
The producer MDR in the comments will refer to the wellspring of the data.
UG-5-6-7-8: BASE MATERIALS
- The Plate, Forgings, Castings, Pipe, and Tubes utilized in the construction of pressure vessels for pressure parts will affirm to the prerequisites of an explicit statement except as in any case allowed.
UG-9: WELDING MATERIALS
- The welding material must conform to the necessities of this code, ASME SEC IX, Qualified WPS, and ASME SEC II Part C.
Material that is produced by specifications that are not permitted by this division is not fully passed or identified accurately.
- Any unknown material (single production lot) for the development of vessel might be acknowledged given the accompanying conditions are met:
i) Recertification will be vessel and part producer as it were.
ii) The documentation will be accessible to show to the part or vessel maker that all the necessities of this code are met. Material checking satisfactory to the investigator.
B) On the off chance that any material with particular which isn’t allowed by ASME Section VIII Div. 1
yet has a place with a specific creation production lot according to the necessities of a detail allowed by this division,
however, which can’t be qualified in the above condition will meet the accompanying conditions to be worthy:
i) Recertification will be by the vessel and part maker as it were.
ii) At the point when documentation exhibiting total conformance to the concoction necessities isn’t accessible, compound examinations are made on various pieces from the parcel to set up a mean investigation that will be acknowledged as illustrative of the lot.
The compound examination will affirm to the details.
iii) Those mechanical properties which are not revealed will be tried and ought to affirm to the detail.
iv) The material if not heat-treated according to particular will be heat treated either preceding or during fabrication.
v) All other appropriate necessities (counting, however not constrained to, melting technique, melting practice,
deoxidation, concoction investigation, mechanical properties, grain size, and nature) of the particular allowed by this Division, to which the material is to be recertified, have been exhibited to have been met.
vi) The material checking will be satisfactory to the examiner and the material will be set apart as required by the determinations.
vii) Material not completely distinguished Won’t talk about this part in detail as it would be prescribed to keep away from such material in pressure vessels.
UG-11: PRESSURE PARTS (PREFABRICATED OR PREFORMED) FURNISHED WITHOUT A CERTIFICATION MARK
- The pressure parts (Prefabricated or preformed) to be utilized for pressure vessels, which are liable to stresses because of pressure and have been outfitted by others or by the producer (of the finished vessel) will fit in with every single pertinent necessity of this Division.
A) Parts that are prefabricated (Preformed) might be provided as follows:
i) Cast, forged, rolled, or die formed non-standard pressure parts: Pressure parts like shells, heads, and so forth that are altogether shaped by
- casting (ex: Shell),
- forging (ex: Nozzle, Shell),
- rolling (ex: Rolled Shell), or
- pass on shaping (ex: Head) that don’t require shop assessment might be provided fundamentally as materials.
ii) Cast (ex: Shell), forged (ex: Nozzle), rolled, or die formed (ex: Head) standard pressure parts that agree to an ASME item standard (ASME SEC II PART-A-B), either welded or consistent.
iii) The Code perceives that an assembling (ASME Certificate Holder) may create parts as per UG-11(d), and that is set apart as per UG-11(d)(8).
iv) Rather than the necessity in UG-11(d)(4)(- a), the producer may subcontract to an individual or association not holding an ASME Certificate standard pressure parts that are fabricated to a standard other than an ASME item standard.
- Bolts and studs might be utilized for the connection of removable parts.
- Studs will be threaded full length or will be machined down to the root breadth of the thread in the unthreaded portion, given that the threaded segments are in any event 11 /2 diameter long in measurements.
- Nuts will comply with the necessities in the appropriate Part of Subsection C (you can refer UCS-11 and UNF-13).
- They will connect with the threads for the full profundity of the nut.
- The utilization of washers is discretionary. At the point when utilized, they will be of wrought materials.E) UG-15: PRODUCT SPECIFICATION
- For a wrought (Forged, Rolled, Extruded and so forth.… ) item when there is no specific detail recorded in subsection C,
- However, there is an affirmed determination recorded in subsection C of some other wrought product of that grade the item for which there is no particular specification that can be given.
1) The chemical and physical properties, heat-treating prerequisites, and necessities for deoxidation, or grain size prerequisites comply with the endorsed determination recorded in Subsection C.
2) The assembling strategies, tolerances, tests, and checking are as per Section II detail covering a similar item structure (Forged, Rolled, Extruded, and so forth… ) of comparative material.
3) For the instance of welded tubing made of plate, sheet, or strip, without the addition of filler metal, the suitable stress values are diminished by 15%.
4) The product isn’t pipe or tubing fabricated by combination welding with the addition of filler metal except if it is fabricated as per the guidelines of this Division as a pressure part.
5) Factory test reports reference the determinations utilized in creating the material and refer to this section.
e) UG-16 : DESIGN:
- The design of pressure equipment and its parts will fit in with the prerequisites in the accompanying passages and notwithstanding the particular necessities given in the appropriate Parts of Subsections B and C.
- Least thickness of pressure holding parts will be 1.5 mm barring corrosion remittance aside from that the above doesn’t matter to heat transfer plates, internal pipe of the double pipe heat exchangers for NPS 6(150) or less.
- The base thickness of shells and heads of unfired steam boilers will be 6 mm selective of any corrosion allowance.
- The base thickness of shells and heads utilized in compressed air administration, steam administration, and water administration, will be 2.5 mm elite of any consumption recompense.
- This minimum thickness doesn’t have any significant effect on the tube in air-cooled and cooling tower heat exchangers if all the accompanying arrangements are met:
i) The tube shall not be utilized for deadly UW-2(a) administration applications.
ii) The tube shall be secured by fins or other mechanical methods.
iii) The tube outside diameter across will be at least 10 mm and a limit of 38 mm.
iv) The minimum thickness utilized will not be not as much as that determined by the formulas given in UG-27 or 1-1 and for no situation under 0.5 mm.
The Plate Under Tolerance:
i) Plate material will not be requested with an ostensible thickness more slender than the design thickness.
ii) Plate material with a real thickness, not exactly the design thickness will not be utilized except if the difference in thicknesses is not exactly the littler of 0.3 mm or 6% of the planned thickness.
iii) On the off chance that plate material is requested to a particular, that permits an under tolerance more prominent than the littler of 0.3 mm or 6% of the ostensible thickness,
the thickness of the plate requested will be increased, whenever required, with the goal that the plate material will meet the prerequisite of (1.5 mm) when utilized.
The Pipe Under Tolerance:
i) Pipe and tube material might be requested by its nominal wall thickness.
Notwithstanding, the assembling under tolerance must be considered when planning or requesting the component.
ii) The under tolerance need not be viewed as when designing nozzle wall reinforcement.
Corrosion Allowance Used in Design Formulas:
i) It is remembered for each dimensional equation utilized in this code.
ii) Examples demonstrating the utilization of the plan rules of this Division are contained in ASME PTB-4, ASME Section VIII, Division 1, and Example Problem Manual.
UG-18: MATERIALS IN COMBINATION
- Any blend of material as referenced in Subsection C of this code can be used the construction of a vessel and joining of different joints prerequisites of ASME SEC IX will be met.
- The standards of the code will oversee the necessities for the parent metal its heat influenced zone (HAZ) and weld metal(s) on the off chance that the parent metals of various metallurgies should be consolidated.
- State, for instance, when SA 516 Gr 70 (Carbon Steel) is welded straightforwardly to SA 240 TP 316L (Austenitic Stainless Steel) utilizing E Ni Cr Fe-3 (SMAW Process) as filler metal the relevant principles of this division will apply to every one of the accompanying independently:
i) CS parent metal and HAZ
ii) ASS parent metal and HAZ
iii) Ni Filler Metal.
UG-19: SPECIAL CONSTRUCTION
Combination units: The types are as follows:
a) Basic Element Design.
b) Differential Pressure Design.
c) Mean Metal Temperature Design.
- At the point when no plan rules are given the maximum admissible working pressure of the finished vessel will be built up as per arrangements of UG-101.
UG-20: DESIGN TEMPERATURE
A) Maximum temperature:
For the parts, the viable greatest temperature will be more prominent than the normal metal temperature through-thickness of the vessel expected in-service except deadly help.
It can be derived by estimation from comparable equipment in service.
(Allude WRC Bulletin 470, “Suggestions for Design of Vessels for Elevated Temperature Service” has data that may demonstrate supportive to the vessel designer).
B) Minimum temperature:
It will be the most minimal expected temperature experienced by the pressure equipment in service
and as needs are the plate, casting, forgings, fittings, and so forth will be chosen for construction.
- The designer will remember the most reduced working temperature in service, the surrounding temperature, the impacts of prompt startup and shut down, and so on while designing the pressure equipment.
Strategies for acquiring the service temperature is additionally referenced in the non-required informative appendix of this code.
- As there is more danger of brittle failure for carbon and low alloy steel so following necessities to be met for impact test exemptions:
(1) For P-No. 1, Gr. No. 1(SA 516 Gr 60) or 2 (SA 516 Gr 70), must be utilized only if the prerequisites of (a) and (b) underneath are met:
(a) Curve A material max thickness confined to 13 mm.
(b) Curve B, C, and D materials thickness confined to 25 mm.
(2) The total pressure equipment to be either hydrostatically or pneumatically tested with the provisions of this code.
(3) The designer will guarantee the temperature extend is among 345°C and – 29°C. Anyway, sporadic temperature underneath – 29°C might be permitted.
UG-21: DESIGN PRESSURE
- Each piece of pressure containing equipment must be intended for a most exceedingly terrible mix of equivalent pressure and temperature expected in normal operation.
The loadings for designing a pressure vessel will incorporate the following:
i) Internal/outer design pressure, test pressure, and coincident static head, abnormal pressure.
ii) Weight of the vessel and normal contents underworking or test conditions.
iii) The inside (Tray Support Ring) and outside connections (Lugs, Skirts, and so forth… )
iv) Wind, day off, seismic responses, impact reactions; superimposed static reactions from the weight of connected equipment (piping, lining and so on.… ), cyclic and dynamic reactions (because of pressure, thermal variations, and so on… … ).
v) Temperature gradients and differential thermal expansion
UG-23: MAXIMUM ALLOWABLE STRESS VALUES
- The Designer will use Section II, Part D, and Sub-section 1 for getting the estimations of the greatest suitable allowable tensile stress implied for various materials.
- For material distinguished as meeting more than one material specification and or grade,
the greatest suitable stress value for either material specification and/or grade might be utilized given all necessities and
impediments to the material determination and grade are met for the maximum allowable tensile stress value chosen.
|1||UCS-23||CS & LAS (Stress Values in Sec II Part D, Sub-part 1, Table 1A & Table 3 respectively.|
|2||UNF 23.1 thru UNF 23.5||Nonferrous metals (Stress Values in Sec II Part D, Sub-part 1, Table 3 and Table 1B).|
|3||UHA-23||HAS (Stress Values in Sec II Part D, Sub-part 1, Table 3 and Table 1A or 1B).|
|4||UCI-23||Max Allowed Tensile Stress for CI.|
|5||UCD-23||Max Allowed Tensile Stress for Cast Ductile Iron.|
|6||UHT-23||Heat Treatment Enhanced Ferritic Steels (Sec II Part D, Subpart1, Table 1A).|
|7||ULT-23||Max Allowed Tensile Stress for 5%, 8% and 9% Ni Steels and 5083-0 Al alloy below -196 Degree C temp for welded and non-welded construction.|
- Designer in designing cylindrical shells or tubes utilizing welded or non-welded item structure will choose the
most extreme admissible compressive stress values in longitudinal way which are exposed to loadings that produce compression in longitudinal direction of the shell or tube be the least of the following:
(1) Max. allowable tensile stress allowed according to code;
(2) Value of B as decided beneath:
E = modulus of elasticity of the material at design temperature.
R0 = outside radius cylinder shell or tube.
t = the minimum thickness of the cylindrical shell or tube.
The joint effectiveness for butt-welded joints will be taken as unity. The estimation of B will be resolved as follows:
Stage 1: Using the estimation of R0 and t,
Calculate factor “A” from the underneath condition:
Stage 2: Enter material outline in Section II Part D Sub-section 3.
Stage 3: If A to one side of the scale (material/temperature line) then extend the appropriate temperature line horizontally to right and read the value of B.
Further to continue reading the ASME Section VIII please read my next article to further get more detail on the remaining portion of the part II.