MAWP AND MDMT CALCULATIONS.pdf

CALCULATIONS TO DETERMINE THE MAXIMUM ALLOWABLE WORKING PRESSURE (MAWP) FOR PRESSURE VESSELS (TANKS 1 AND 2) IN ACCORDANCE WITH API510 TENTH EDITION 2014; PRESSURE VESSEL INSPECTION CODE: INSERVICE INSPECTION, RATING REPAIR AND ALTERATION SECTION 7.3 Maximum Allowable Working Pressure (MAWP) Determination The MAWP for the continued service of a pressure vessel shall be based on the computations that are determined using the latest applicable edition of the ASME code or the construction code to which the vessel was built. The resulting MAWP from these computations shall not be greater than the original MAWP unless a rerating is performed. The wall thickness used in these computations shall be the actual thickness as determined by inspection when multiple thickness measurement shall be taken.

SECTION 7.7

Evaluation of Existing Equipment with Minimal Documentation

For pressure vessel that has no name plate and minimal or no design and construction documentation, the following steps maybe used to verify operating integrity: 1. Perform inspection to determine condition of the vessel and determine minimum thickness values and adequacy of the design of the vessel 2. Define design parameters 3. Perform design calculations based on applicable codes and standards 4. Do not use allowable stress values of current ASME code (based on design factor of 3.5); for older vessels allowable stress values have been based on a design factor 4.0 to 5.0 5. For carbon steel, use allowable stress values for SA-283 Grade C and joint efficiency of 0.7 for type No.1 6. Attach a name plate or stamping showing MAWP, MDMT, Material Specification, Date, etc, (as deemed necessary by the owner/user) 7. Perform pressure test as soon as practical as required by code or at the discretion of the owner/user

ASME BOILER AND PRESSURE VESSEL CODE; SECTION VIII-DIVISION I; RULES FOR THE CONSTRUCTION OF PRESSURE VESSELS SUBSECTION A UG-1 SCOPE The requirements of part UG in the ASME code are applicable to all pressure vessel and vessel parts and shall be used in conjunction with the specific requirements in subsection B and C and the mandatory Appendix that pertain to the method of fabrication and the material used. 1

UG-4 MATERIALS (a) Materials subject to stress due to pressure shall conform to one of the specification given in ASME BPVC section II, Part D, subpart I, Tables IA, IB, and 3, including all applicable notes in the tables, and shall be limited to those that are permitted in the applicable part of subsection C, except as otherwise permitted in UG-9, UG-10, UG11, UG-15, Part UCS, Part UIG and the mandatory appendices.

UG-16 DESIGN MINIMUM THICKNESS OF PRESSURE RETAINING COMPONENTS Except for special provisions, the minimum thickness permitted for shells and heads after forming and regardless of product form and material, shall be 1/16inch (1.5mm) exclusive of any corrosion allowance.

UG-98 MAXIMUM ALLOWABLE WORKING PRESSURE UG-98 (a) The MAWP for a pressure vessel is the maximum pressure permissible at the top of the vessel in its normal operating position at the designated coincident temperature specified for that pressure. It is the least of the values found for MAWP for any of the essential parts of the vessel by the principles given in (b) below, and maybe adjusted for any difference static head that may exist between the part considered and the top of the vessel. UG-98 (b) The MAWP for a vessel part is the maximum internal or external pressure as determined by the rules and formulae of the ASME division. MAWP may be determined for more than one designated operating temperature, using for each temperature the applicable allowable stress value. 1-1 THICKNESS OF CYLINDRICAL AND SPHERICAL SHELLS 1. FOR CYLINDRICAL SHELLS (CIRCUMFERENTIAL STRESSES) CIRCUMFERENTIAL STRESS (LONGITUDINAL JOINTS) When the thickness does not exceed one-half of the inside radius or P does not exceed 0.385SE; the following formulae shall apply;

P = SEt/R0 - 0.4t E = Joint Efficiency for cylindrical shells. For welded vessels we use the efficiency specified UW-12/API 510 P = Internal Design Pressure R0 = Outside radius of shell course under consideration 2

t = Minimum thickness of shell course S = Maximum allowable stress value S; Maximum allowable stress value; UG-23; this is the maximum unit stress permitted in a given material used in a vessel constructed under these rules. The maximum allowable tensile stress values permitted for different materials are given in: SUBPART I of ASME BPVC SECTION II MATERIALS, PART D; TABLE UCS CARBON AND LOW ALLOY STEEL. The MDMT (Minimum Design Metal temperature) shall correspond to a coincident pressure equal to the MAWP. The design temperatures are coincident with the maximum allowable stress needed to calculate the design pressure. Therefore, design temperatures that exceed the temperature limit in the applicability column shown section II Part D, subpart I, table IA are not permitted. All carbon and low alloy steel materials subject to stresses due to pressure shall conform to one of the specification given in ASME BPVC Section II and shall be limited to those in table UCS-23, except as otherwise provided in UG-10 and UG-11.

TABLES 1A provides Allowable Stress for Ferrous Materials used in the ASME BPVC code Section II, Part D; Ferrous materials. For SA-283 Grade C: Minimum specified tensile Strength = 380Mpa (55Ksi); P-No.1; Group No.1; Nominal Composition – carbon steel- Plate. MAXIMUM ALLOWABLE STRESS VALUES ‘’S’’ @ DIFFERENT MDMT MDMT(OC) -30 - 40 OC 65 OC 100 OC 125 OC 150 OC 200 OC 250 OC 300 OC 325 OC 350 OC

‘’S’’ (Mpa) 108Mpa 108Mpa 108Mpa 108Mpa 108Mpa 108Mpa 108Mpa 107Mpa 104Mpa 101Mpa

MAXIMUM TEMPERATURE LIMIT = 343 OC Therefore, we shall take a value of -30 OC for our MDMT and our ‘’S’’ value shall be 108Mpa. From UG-23; the maximum allowable stress value ‘’S’’ that are to be used in the calculations are to be taken from the tables at the temperature that is expected to be maintained in the metal under the conditions of loading being considered.

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MAWP CALCULATIONS; FOR PRESSURE VESSEL (TANK 1) E = 0.7 S = 108Mpa R0 = 477.4mm t

= 8.4mm

P = SEt/R0 – 0.4t P = 108,000,000 X 0.7 X 8.4/477.4 – 0.4 X 8.4 P = 635,040,000/474.04 P = 1,339,633.786 Pascal P = 1.339Mpa P = 1.34Mpa

TO CHECK IF THE FORMULAE APPLIES: P MUST NOT EXCEED 0.385SE THEREFORE: 0.385SE = 0.385 X 108,000,000 X 0.7 = 29,106,000

THEREFORE, FROM THE ABOVE CALCULATION, P DOES NOT EXCEED 0.385SE; THE FORMULAE APPLIES AS A PRINCIPLE IN THE ASME BPVC CODE. FOR TANK1 (PRESSURE VESSEL) MAWP = 1.34Mpa/194.351Psi/13.4Bar @250 OC MDMT = -30 OC@ 1.34Mpa

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MAWP CALCULATION FOR TANK 2 (PRESSURE VESSEL) E = 0.7 S = 108Mpa R0 = 477.4mm t = 8.5mm

P = SEt/R0 – 0.4t P = 108,000,000 X 0.7 X 8.5/477.4 – 0.4 X 8.5 P = 642,600,000/474 P = 1,355,696.203 Pascal P = 1.355Mpa

ALREADY, WE HAVE VERIFIED FROM ABOVE THAT; P DOES NOT EXCEED 0.385SE.

FOR TANK 2 (PRESSURE VESSEL) MAWP = 1.355Mpa/196.53Psi/13.55Bar@250 OC MDMT = -30 OC @ 1.355Mpa

REFERENCED DOCUMENTS: 1. API 510; TENTH EDITION; 2014; PRESSURE VESSEL INSPECTION CODE; INSERVICE INSPECTION, RATING, REPAIR AND ALTERATION 2. ASME BOILER AND PRESSURE VESSEL CODE; SECTION II; MATERIALS PART D (METRIC) 3. ASME BOILER AND PRESSURE VESSEL CODE; SECTION VIII, DIVISION I; RULES FOR THE CONSTRUCTION OF PRESSURE VESSELS 4. ASME BOILER AND PRESSURE VESSEL CODE; SECTION IX; WELDING AND BRAZING QUALIFICATIONS

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