CAPÍTULO 1: MARCO TEÓRICO
1.2. Conceptos
5.7.1. This section provides additional requirements for vessels designed to operate in special services.
The designer is cautioned to ensure the appropriate requirements for each applicable service environment are addressed and that more than one service requirement may be applicable.
5.7.2. Material and Fabrication Requirements for Equipment in Sour, Amine, Caustic, Hydrogen, Hydrofluoric Acid or Cyclic service as described in paragraphs 4.8 thru 4.13
5.7.2.1. Stamping or indentation marking shall not be allowed on a vessel internal surface for clad equipment.
5.7.2.2. For new construction, no welding, hammering or cutting shall be performed after PWHT.
Any grinding performed after PWHT shall ensure metal temperatures are kept below 500°F (260°C).
5.7.2.3. Connections smaller than NPS 1½” shall not be used.
5.7.2.4. All internal attachment welds shall be full penetration type.
5.7.3. Material and Fabrication Requirements for Equipment in Sour Service or Hydrofluoric (HF) Acid Service
5.7.3.1. Base materials shall conform with requirements of NACE MR0103 or MR0175/ISO 15156 as applicable.
5.7.3.2. Carbon Steel plates shall have the following requirements;
a. Vacuum degassed and normalized.
b. Material chemistry shall be restricted as follows;
INT i. S ≤ 0.003%
ii. P ≤ 0.012%
iii. V ≤ 0.015%
iv. Cb ≤ 0.015%
v. V + Cb ≤ 0.02%
Chemical analysis reported on Certified Material Test Reports shall include Cb, V, Ti, S, P, Ni, Mo, Cr, Cu
5.7.3.3. Plates shall be 100% UT examined, in accordance with ASME SA 578 Scanning S1, acceptability Level C. Repair of defects requires Owner’s Engineer approval.
5.7.3.4. For carbon steels, the maximum permissible Carbon Equivalent (C.E.) for plate materials shall be 0.43 for materials less than 1” thick and 0.45 for thicknesses 1 inch and greater where;
C.E. = C + Mn/6 + (Ni + Cu)/15 + (Cr + Mo + V)/5 where all values are in weight percent.
Deliberate additions of Boron or Titanium are not permitted.
5.7.3.5. All cold formed heads of carbon or low alloy steels shall be stress relieved or normalized after forming. If the hot forming temperature is equal to or greater than the normalizing temperature then additional normalizing heat treatment after completion of forming will not be required. In the case that normalizing is provided then the mechanical properties of material shall be reconfirmed.
5.7.3.6. MP or PT examination shall be carried out on all formed surfaces (knuckles and flares) such as formed heads and conical transitions.
5.7.3.7. After forming process, the following supplementary NDE shall be performed on all formed heads fabricated from welded segments.
a. All welds between the segments shall be 100% RT examined in accordance with ASME Code, Section VIII, Div.1 or Div.2.
b. All welds between the segments shall be MT or PT examined in accordance with ASME Code, Section VIII, Div.1 or Div.2.
5.7.3.8. Carbon steel forgings except the standard components such as flanges fabricated in accordance with ASME B16.5 or B16.47 shall be;
a. 100% UT examined (after machining) in accordance with ASME SA 388 and ASME Code Section V Article 5. Any defect which does not meet the requirements presented in ASME Code Section VIII Div.1 Appendix 12 or Section VIII Div.2 paragraph 3.3.4, shall be rejected.
b. Vacuum degassed and normalized or quenched and tempered.
c. Provided with material chemistry restricted as follows;
INT i. S + P ≤ 0.015%
ii. C.E. ≤ 0.45%.
5.7.3.9. Bolting material which is part of a vessel pressure envelope shall be ASME SA 193, Gr.
B7M (bolts) and ASME SA 194, Gr. 2HM (nuts).
5.7.3.10. For carbon and low alloy steels, PWHT shall be required after fabrication is complete.
5.7.3.11. All internal attachment welds shall be full penetration type and designed to permit access for inspection.
5.7.3.12. Welds on vessels shall be examined as follows;
a. “FULL” RT of butt welds in accordance with the definition provided in ASME Code Section VIII, Div.1 paragraphs UG-116 (e)(1) and UW-11(a)(2) to UW-11(a)(4) and stamped “RT-1”.
b. Manual UT examination in accordance with ASME Code Section VIII, Div.1, Appendix 12 or ASME Code Section VIII, Div.2, paragraph 7.5.4 shall be applied on category D (Corner welds) of pressure envelope.
INT
c. For carbon and low alloy steels, WFMT examination is required according to ASME Code Section VIII, Div.1, Appendix 6 or ASME Code Section VIII, Div.2, paragraph 7.5.6 on all accessible internal welds.
5.7.3.13. For severe sour services, the designer may consider the use of corrosion resistant weld overlay, cladding or solid alloy construction in lieu of carbon steel construction to address corrosion and cracking risks. This decision will be subject to Owner’s Engineer approval.
5.7.4. Material and Fabrication Requirements for Carbon Steel Equipment in Amine Service
5.7.4.1. All equipment shall be PWHT after fabrication is complete to avoid Amine Stress Corrosion Cracking (ASCC).
5.7.5. Material and Fabrication Requirements for Hydrogen Service
5.7.5.1. Carbon steel shall not be used in fabrication of vessels exposed to Hydrogen Service (paragraph 4.10).
5.7.5.2. On vessels in hydrogen service, the weld detail between the nozzle and vessel envelope shall be in accordance with ASME Sec.VIII, Div.1, figure UW-16 (f-2) and (f-4) or Sec.VIII, Div.2, table 4.2.13 so that they can be RT examined.
5.7.5.3. All external attachments on vessels operating in Hydrogen Service, shall be welded with full penetration on the pressure envelope.
5.7.5.4. All nozzles shall be integrally self reinforced type.
5.7.5.5. The attachment between the bottom head and skirt support shall be provided as a weld build-up or as a forged ring.
5.7.5.6. Leg or lug type supports may not be used.
5.7.5.7. Reinforcing pads shall not be used.
5.7.5.8. All welds shall be ground smooth to eliminate sharp corners and edges. A gradual transition from weld surface to the base metal is required to eliminate stress concentration points.
5.7.5.9. MP or PT examination shall be carried out on all formed surfaces (knuckles and flares) such as formed heads and conical transitions.
5.7.5.10. After forming process, the following supplementary NDE shall be performed on all formed heads fabricated from welded segments;
a. All welds between the segments shall be 100% RT examined in accordance with ASME Code, Section VIII, Div.1 or Div.2.
b. All welds between the segments shall be MT or PT examined in accordance with ASME Code, Section VIII, Div.1 or Div.2.
5.7.5.11. All cold formed heads made of low alloy steel shall be stress relieved or normalized after forming. If the hot forming temperature is equal to or greater than the normalizing
temperature then additional normalizing heat treatment after completion of forming will not be required. In the case that normalizing is provided then the mechanical properties of material shall be reconfirmed.
5.7.6. Material and Fabrication Requirements for Caustic Service
5.7.6.1. Equipment in caustic service shall be designed in accordance with requirements in Figure 1, Caustic Soda Service Chart, of NACE RP0403-2003. The requirements for PWHT shall also be applicable to cold formed heads.
5.7.7. Material and Fabrication Requirements for Cyclic Service
5.7.7.1. The following requirements are in addition to those given in paragraph 5.2.5 for cyclic loads.
5.7.7.2. Where conical elements are used they shall be complete with torical transitions on the large end (knuckle type).
5.7.7.3. “Set-on” type nozzles shall not be used.
5.7.7.4. The mean diameter of the heads shall match the mean diameter of the skirt support.
5.7.7.5. Leg or lug type supports may not be used.
5.7.7.6. Reinforcing pads shall not be used.
5.7.7.7. All welds shall be ground smooth to eliminate sharp corners and edges. A gradual transition from weld surface to the base metal is required to eliminate stress concentration points.
APPENDIX A – TYPICAL FABRICATION MATERIALS
A.1. PLATES
Material ASME P no. ASME Standard
Carbon Steels - P1 P1 SA 516 Gr.70 & 65 & 60
Low alloy Steels - (1 Cr – ½ Mo) P4 SA 387.12 Cl.1 & 2 Low alloy Steels - (1¼ Cr – ½ Mo – Si) P4 SA 387.11 Cl.2 Low alloy Steels - (2¼ Cr – 1 Mo) P5A SA 387.22 Cl.1 & 2
Low alloy Steels - (2¼ Cr – 1 Mo – ¼ V) P5C SA 832.22V; SA 542.D Cl.4a Low alloy Steels - (3 Cr – 1 Mo) P5A SA 387.21 Cl.1 & 2
Low alloy Steels - (3 Cr – 1 Mo – ¼ V) P5C SA 832.21V; SA 542.C Cl.4a High alloy Steels - P8 (e.g.: 304L, 316L, 317L) P8 SA 240
A.2. SMALL FORGINGS
Material ASME P no. ASME Standard
Carbon Steels - P1 P1 SA 105; SA 350.LF2
Low alloy Steels - (1 Cr – ½ Mo) P4 SA 182.F12 Cl.1 & 2 Low alloy Steels - (1¼ Cr – ½ Mo – Si) P4 SA 182.F11 Cl.1 & 2 Low alloy Steels - (2¼ Cr – 1 Mo) P5A SA 182.F22 Cl.1 & 3 Low alloy Steels - (2¼ Cr – 1 Mo – ¼ V) P5C SA 182.F22V Low alloy Steels - (3 Cr – 1 Mo) P5A SA 182.F21 Low alloy Steels - (3 Cr – 1 Mo – ¼ V) P5C SA 182.F3V High alloy Steels - P8 (e.g.: 304L, 316L, 317L) P8 SA 182 A.3. LARGE FORGINGS
Material ASME P no. ASME Standard
Carbon Steels - P1 P1 SA 266.2; SA 266.4
Low alloy Steels - (1 Cr – ½ Mo) P4 SA 336.F12
Low alloy Steels - (1¼ Cr – ½ Mo – Si) P4 SA 336.F11 Cl.1 & 2 & 3 Low alloy Steels - (2¼ Cr – 1 Mo) P5A SA 336.F22 Cl.1 & 3 Low alloy Steels - (2¼ Cr – 1 Mo – ¼ V) P5C SA 336.F22V Low alloy Steels - (3 Cr – 1 Mo) P5A SA 336.F21 Cl.1 & 3 Low alloy Steels - (3 Cr – 1 Mo – ¼ V) P5C SA 336.F3V
High alloy Steels - P8 (e.g.: 304L, 316L, 317L) P8 SA 336 A.4. PIPES
Material ASME P no. ASME Standard
Carbon Steels - P1 P1 SA 106.B; SA 333.6
Low alloy Steels - (1 Cr – ½ Mo) P4 SA 335.P12 Low alloy Steels - (1¼ Cr – ½ Mo – Si) P4 SA 335.P11
Low alloy Steels - (2¼ Cr – 1 Mo) P5A SA 335.P22; SA 369.FP22 Low alloy Steels - (2¼ Cr – 1 Mo – ¼ V) P5C N/A
Low alloy Steels - (3 Cr – 1 Mo) P5A SA 369.FP21 Low alloy Steels - (3 Cr – 1 Mo – ¼ V) P5C N/A
High alloy Steels - P8 (e.g.: 304L, 316L, 317L) P8 SA 312
A.5. FITTINGS
Material ASME P no. ASME Standard
Carbon Steels - P1 P1 A 234.WPB; SA 420.WPL6
Low alloy Steels - (1 Cr – ½ Mo) P4 SA 234.WP12.Cl.1, SA 369.FP12 Low alloy Steels - (1¼ Cr – ½ Mo – Si) P4 SA 234.WP11.Cl.1, SA 369.FP11 Low alloy Steels - (2¼ Cr – 1 Mo) P5A SA 234.WP22.Cl.1, SA 369.FP22 Low alloy Steels - (2¼ Cr – 1 Mo – ¼ V) P5C N/A
Low alloy Steels - (3 Cr – 1 Mo) P5A N/A
Low alloy Steels - (3 Cr – 1 Mo – ¼ V) P5C N/A High alloy Steels - P8 (e.g.: 304L, 316L, 317L) P8 SA 403
APPENDIX B – SUPPLEMENTARY REQUIREMENTS FOR VESSELS FABRICATED OF 1 CR-½ MO AND 1¼ CR-½ MO STEELS
Unless otherwise specified, all materials type 1 Cr-½ Mo and 1¼ Cr-½ Mo shall meet the following supplementary requirements;
B.1. MATERIALS
B.1.1. At design temperatures of 750°F (399°C) and higher, in hydrogen service;
B.1.1.1. Roll bonded cladding shall be avoided due to the possibility of disbonding caused by hydrogen. Where cladding is required, explosion bonded cladding or weld overlay shall be used to protect the vessel internal surface.
B.1.1.2. The materials used for fabrication of the pressure envelope shall be Quenched and Tempered (Q&T).
B.1.2. Chemical analysis for each material heat. As a minimum the analysis shall present the
concentration (%) of the following elements; C, Si, Mn, Cr, Mo, V, Nb, Ti, Cu, Ni, P, S, Sn, Sb, As.
The materials shall have the following restricted chemistry;
B.1.2.1. C < 0.15%
B.1.2.2. Cu < 0.20%
B.1.2.3. Ni < 0.30%
B.1.2.4. P < 0.007%
B.1.2.5. S < 0.007% or (S+P < 0.014%)
B.1.2.6. PSR = Cr + Cu + 2 x Mo + 10 x V + 7 x Nb + 5 x Ti – 2 < 0 reference [3.2.6.3]
B.1.2.7. X bar = (10 x P + 5 x Sb + 4 x Sn + As) / 100 < 15 reference [3.2.6.3]
B.1.2.8. The chemistry shall be tested with a frequency of one per each melt, heat or batch.The chemistry shall be tested with a frequency of one per each melt, heat or batch.
B.1.3. On quench and tempered materials, tensile tests at room and design temperature shall be performed. The tested material shall have been subjected to an equivalent of 3 PWHT. The yield strength shall not be lower than the tabulated values presented in ASME Sec. II D, table “Y-1”.
B.1.4. Charpy V impact tests shall be performed according to the methodology presented in API 934A to determine the temperature at which the absorbed energy is 40 ft-lb (T40 temperature). A minimum of 18 specimens (3 specimens at 6 different temperatures) shall be used to generate the transition temperature curve. The tested material shall have been exposed to an equivalent of 3 PWHT cycles. The T40 temperature shall be used as reference value to determine vessel MDMT. The test shall be applied on each heat and/or batch of material (plates, pipes, fitting, forgings).
INT
B.1.5. Hardness shall not exceed 225 BHN. Test frequency to be 3 tests per each heat or batch.
B.1.6. 100% UT examination shall be provided on all custom forgings (after machining) and plates (heads after forming) used for pressure envelope. As a minimum, the test shall be done as follows;
B.1.6.1. All forgings - Surface scan in accordance with SA 388 and ASME Sec. V, Article 5. For vessels designed to operate in Hydrogen Service, in addition to ASME acceptance criteria, any defect which cannot be encompassed within ¼” (6 mm) diameter sphere, shall be rejected.
B.1.6.2. All plates - Full surface scan in accordance with SA 578 scanning S1. The acceptance level is Level C. For vessels designed to operate in Hydrogen Service, in addition to ASME acceptance criteria, any defect which cannot be encompassed within ¼” (6 mm) diameter circle, shall be rejected.
B.1.7. All welding consumables to be used shall have the “X” factor limited to 15. The Cu and Ni content shall be limited to 0.20% and respectively 0.30%. Minimum test frequency shall be one per each heat.
B.2. FABRICATION
B.2.1. All nozzles shall be self reinforced type.
B.2.2. The nominal chemistry of welding consumables shall match the nominal chemistry of the base materials.
B.2.3. All welding consumables shall be low hydrogen (max. of 8 ml hydrogen per 100 g of weld metal) H8 as per AWS 4.3. The coated consumables as well as the flux shall be baked and stored in accordance with manufacturer’s specifications.
B.2.4. The qualification of each WPS shall include Charpy V impact test provided to determine the temperature at which the absorbed energy is 40 ft-lb (T40). This temperature shall be used as reference value to determine the vessel MDMT. Minimum 18 (eighteen) specimens extracted from a weld deposit coupon shall be used to determine T40.
INT
B.2.5. All welds performed on pressure envelope (including the attachment welds) shall be preheated at a minimum temperature of 300°F (149°C) through all base metal thickness. The preheating shall be maintained during the welding process. For welds 3” and thicker the preheat shall be
maintained without interruption until its completions when a DHT or ISR will be provided.
B.2.6. Any attachment weld to the pressure envelope shall be full penetration type. The transition between the attachment and vessel envelope shall be ground smooth and flush to the vessel surface with a transition radius not smaller than ¼” (6 mm).
B.2.7. External clips attached to the pressure envelope shall be;
B.2.7.1. Fabricated from materials with similar chemistry as the vessel base metal and shall be attached, by a full penetration weld, directly to the vessel surface.
B.2.7.2. The clips may be fabricated from different type of steel welded on top of a buttering layer applied on the vessel surface. The clip shall be welded on top of this layer with full penetration.
B.2.8. On vessels with a wall thickness exceeding 3” (75 mm), after completion of welding an
Intermediate Stress Relief (ISR) heat treatment shall be performed on all restrained welds (such as welds around the nozzles). The ISR shall be provided at minimum 1100°F (593°C) for a period of time not shorter than 2 hours.
B.2.9. On vessels with a wall thickness exceeding 3” (75 mm), all circumferential and longitudinal butt welds shall receive a Dehydrogenation Heat Treatment (DHT). The DHT shall be provided at minimum 600°F (316°C) for a period of time not shorter than 2 hours.
B.2.10. The final PWHT shall be performed at a minimum temperature of 1275°F (691°C). The PWHT temperature shall be maintained constant for a period of time equal to;
Total minimum time [hours] = Shell thickness [in] x 1 hour B.3. NON DESTRUCTIVE EXAMINATION (NDE)
B.3.1. The following NDE sequence shall be provided during the fabrication process;
B.3.1.1. The following NDE shall be performed prior to final PWHT;
B.3.1.1.1. MT examination on all edges prepared for welding (plates and forgings).
B.3.1.1.2. MT examination of formed plates required on pressure envelope (on heads after forming).
B.3.1.1.3. MT examination of any temporary external attachment welds, after they have been removed and the surface ground smooth.
B.3.1.1.4. RT examination of all pressure retaining butt welds. RT examination can be replaced by computerized UT examination in accordance with Code Case 2235 and standard PQA-GS-0019.
B.3.1.1.5. Where applicable, RT examination on all butt welds of the Cr-Mo portion of the skirt support.
B.3.1.1.6. Where internal ring supports (fabricated as weld build-up or full penetration welded on vessel surface) are provided, manual UT examination of the junction between vessel surface and internal support rings (provided from outside of pressure envelope).
B.3.1.1.7. Where applicable, 10% UT examination of weld overlay bonding (provided from outside of pressure envelope).
B.3.1.1.8. Where applicable, PT examination on entire surface of the first layer of weld overlay (applicable only if a second layer of weld overlay will be applied after final PWHT).
B.3.1.1.9. Where 300 series stainless steel weld overlay is applied on vessel internal surface, Ferrite number readings of the weld overlay are required before final PWHT. The limitation of ferrite content shall be in accordance with Standard 0903. Readings are required on each element covered with weld overlay as well as on each weld overlay restoration applied over the circular seams. Test frequency is one reading per each weld overlay restoration and each surface covered with weld overlay.
B.3.1.2. The following NDE shall be performed after final PWHT but prior to the hydrotest;
B.3.1.2.1. RT examination of all pressure retaining butt welds. RT examination can be replaced by computerized UT examination in accordance with Code Case 2235 and standard PQA-GS-0019. For vessel designed in accordance with ASME Section VIII Div.2 the
computerized UT examination shall follow the requirements provided in paragraph 7.2.2 of the Code.
B.3.1.2.2. All the other pressure retaining welds shall be manual UT examined.
B.3.1.2.3. Where applicable, manual UT examination of the junction between vessel surface and internal support rings (from outside).
B.3.1.2.4. Where applicable, manual UT examination of the junction between pressure envelope and skirt support.
B.3.1.2.5. Where applicable, manual UT examination of the weld overlay deposit, from outside, as follows;
a. All surfaces covered with weld overlay applied on nozzles.
b. All weld overlay applied over the base metal seams.
B.3.1.2.6. Where applicable, manual UT examination of the weld overlay surface within 2” on both sides of support rings as well as on the machined surfaces of weld overlay (from inside). The examined surface shall be free of any disbondment.
B.3.1.2.7. Where applicable, PT examination of all finished weld overlay surfaces.
B.3.1.2.8. Hardness tests of the weld deposit after final PWHT. Test frequency shall be two (2) locations per weld. The maximum hardness shall not exceed the limit provided in Standard 0903. The tests shall be performed on external surface.
B.3.1.2.9. Hardness tests on the weld deposit of all butt welds located on the Cr-Mo portion of skirt support. The test frequency shall not be less than two (2) locations per weld.
The maximum hardness shall not exceed 225 BHN.
B.3.1.3. The following NDE shall be performed after hydrotest;
B.3.1.3.1. MT examination of all external attachment welds.
B.3.1.3.2. Where applicable, MT examination of the junction between the skirt and vessel envelope.
B.3.1.3.3. MT examination of all butt welds on pressure envelope (from outside) and from inside if there is no internal cladding/weld overlay.
B.3.1.3.4. If internal cladding and/or weld overlay is applied on vessel internal surface, PT examination of all internal attachment welds.
B.3.1.4. Chemical analysis tests of 300 series stainless steel weld overlay. As a minimum, the concentration of the following elements shall be provided in the inspection report; C, Cr, Ni, Cb, Mo and V. The acceptable limits shall be in accordance with the requirements provided in Standard 0903.
B.3.1.5. Production Charpy V impact tests on the weld metal and HAZ at the temperature determined in accordance with the requirements presented in paragraph B.2.4. One set of 3 specimens shall be provided for each WPS and for each batch of welding
consumables. The specimens shall be heat treated to an equivalent of 3 PWHT cycles.
The absorbed energy shall not be lower than 40 ft-lb. Run-off tabs shall be used wherever possible.
APPENDIX C – SUPPLEMENTARY REQUIREMENTS FOR VESSELS FABRICATED OF 2¼ CR-1 MO, 2¼ CR-1 MO-¼ V, 3 CR-1 MO AND 3 CR-1 MO-¼ V STEELS
The requirements presented in this appendix are supplementing the requirements for design and fabrication of vessels designated to operate in Hydrogen Service at high pressure and high temperature (reference 3.2.6.4).
C.1. DESIGN
C.1.1. At design temperatures of 750°F(399°C) and higher, in hydrogen service, roll bonded cladding shall be avoided due to the possibility of disbonding caused by hydrogen. Where cladding is required, explosion bonded cladding or weld overlay shall be used to protect the vessel internal surface.
C.1.2. The shell components shall be fabricated as follows;
C.1.2.1. Integrally forged cylinders for wall thickness exceeding 6” (150 mm).
INT
C.1.2.2. Rolled plates for wall thickness 6” (150 mm) or smaller.
C.1.3. For thicknesses exceeding 2” (50 mm), the formed or forged heads shall be hemispherical type.
C.1.4. On vertical vessels, the junction between the bottom head and the skirt support shall be designed as follows;
C.1.4.1.1. Integral forged ring (“Y” ring), fully machined, in accordance with ASME Sec.VIII, Div.2 table 4.2.5, detail 7.
C.1.4.1.2. Machined weld build-up. All corners and transitions of the weld build-up shall be rounded in order to reduce stress concentrations. Minimum radius shall not be less than ½” (12 mm).
C.1.4.1.3. Within the limitations imposed by shell thickness, the end of the shell may be fully machined to accommodate the transition required to bottom head and skirt support.
C.1.4.1.3. Within the limitations imposed by shell thickness, the end of the shell may be fully machined to accommodate the transition required to bottom head and skirt support.