ASME B 31 simplified

Training Program on Code Awareness ASME B 31.1 Various Piping Codes: Committee’s were formed to look into various piping application areas and come out with codes for safety of operation. Accordingly this was initiated in the year 1926 and published thru 1942 thru 1955. Presently the following codes are in force designated as ASME B 31 piping. Previously it was under ANSI. ASME B 31.1 B 31.3 B 31.4 B 31.5 B 31.8 B 31.9 B 31.11

Power Piping Process Piping liquid transportation system for hydrocarbon, L.P.G., Anhydrous ammonia, alcohol Refrigeration Piping Gas transmission and distribution piping system Building Service piping Slurry Piping

ASME B 31.1 : this code was written with power piping in mind included to cover fuel gas and oil systems in the plant, central and district heating system, in addition to water and steam systems in power plants. At present B 31.9 covers service piping into buildings. In case the limit of B 31.9 is exceeded it will fall under B 31.1. Scope and exemptions are covered under para 100.1.2 and 100.1.3. This code is for making new piping. It can be used as a guide for repair / replacement. Organization of B 31.1 : Boiler External and Non boiler External Piping : The code has separate requirement for boiler external and non boiler external piping. Boiler external piping is actually within the scope of Secton I of B&PV code. Section I refers to B31.1 for technical requirement. Non boiler external piping falls entirely within the scope of B 31.1. thus boiler external piping is treated as part of boiler whereas nonboiler external piping is not. Boiler external piping is considered to start at the first weld for welded pipe, flanged face for flanged piping, or threaded joint for threaded piping outside of the boiler. It extends to the valve or valves required by Section I.( See para 122 of B 31.1) Both the joint with the boiler proper piping and the valves at the end of the piping fall within the scope of boiler external piping. Systems Covered under B 31.1 : 1) boiler external piping including steam, feedwater, blowoff, and drain piping; 2) instrument, control, and sampling piping; 3) spray-type desuperheater piping for use on steam generators and reheat piping;

4) 5) 6) 7)

piping downstream of pressure reducing valves; pressure-relief piping; piping for flammable and combustible liquids; piping for flammable gased, toxic gases or liquids, or non flammable non toxic gases; 8) piping for corrosive liquids and gases; 9) temporary piping systems; 10) steam trap piping; 11) pump-discharge piping; and 12) district heating and steam distribution systems. Code consists of six chapters and 13 appendices. Appendices with a letter designation are mandatory; those with a Roman numeral designation are non mandatory. All paragraphs in the code are in the 100 range. The 100 series para are the B 31.1 code section of B31 code for pressure piping. Design Conditions and Criteria : Design conditions are specifically intended for pressure design. Design pressure and temperature are the most severe coincident conditions that result in the greatest pipe wall thickness or highest required pressure class or other component rating. In determining the design pressure, all conditions of internal pressure must be considered. This includes thermal expansion of trapped fluids, surge and failure of control devices. Determination of design pressure can be significantly affected by means used to protect pipe from overpressure.( See para 122) For example boiler external piping the design pressure is required to exceed 25% or 225 psi whichever is less. Refer to para 102.2.4 for short term conditions. Design Temperature : It is the metal temperature that is of interest in establishing the design temperature. Design metal temperature is not permitted to be less than the average of fluid temperature and oustside surface temperature. Allowable stress value of metallic piping is given in Appendix – A. Allowance for temperature and pressure variations permitted for short term events as long as several conditions are satisfied. Overpressure protection for safety should be taken into account for design. Pressure Design : (Internal Pressure ) Methods of internal pressure design as per para 102.2

Components listed in Table 126.1 for which pressure ratings are provided in standard such as B 16.5 are considered suitable by B 31.1. Design calculations are made for straight pipe and matching fittings are suitably selected. Design equations for some components such as straight pipe and branch connections are provided in Para 104 of B31.1. Specifically designed components that are not covered by standards listed in table 126.1 and for which design formulas and procedures are not given in B31.1 may be designed for pressure in accordance with para 104.7.2 Allowances such as for corrosion/ erosion, material removal in threads and groovings are to be added to minimum required thickness. Pressure Design : ( External Pressure ) For straight pipe under external pressure there is a membrane stress check in accordance with equation used for internal desing pressure as well as a buckling check in accordance with external pressure design rules of B&PV code Sec VIII div 1 ( para UG 28, UG 29, UG 30) Flanges, heads and stiffeners that comply with section VIII div 1, para UG 29 are considered stiffeners. Length between stiffeners is the length between such components. For determination of factor A and B refer to chart of relevant section. Pressure Design for Welded branch Connections: Reinforcement principle is applied for welded branch connection. Angle alpha between run pipe and branch pipe is atleast 45deg . when the above limitation are not satisfied the designer is directed to para 104.7. Alternative in that a para include proof testing and finite element analysis. Pressure Design of Extruded outlet header: Para 104.3.1(G) provides area replacement rules for such connections. They are applicable for 90 deg branch connection. Additional considerations for branch connection under external pressure is covered under para 104.3.1. Branch connection that are presumed to be acceptable are fittings listed in Table 126.1(eg. B16.9 tees, MSS SP-97 branch outlet fittings. Para 104.3.1.(C) Pressure Design of Bends and Elbows: Minimum wall thickness as required by straight pipe in para 104.1

Pressure Design of miters: Para 104.3.3, 104.7, 104.3.3 ( C ) Pressure Design of Closures: Para 104.4.1, PG 31 of Section I or UG 34 & UW 13 of Section VIII div 1 or 104.7 Pressure Design of Flanges, Blank flanges, Blanks,reducers: Para 104.5.1 and appendix 2 of Section VIII div1 for flanges Para104.5.2 for blind flanges Para 104.5.3 for blanks Para 104.6, 104.7 for reducers Specially designed component as per para 104.7.2 Limitation on components and joints refer to chapter II of B31.1 part3 & 4 which includes valves, Flanges, fittings, bends, miters and branch connection, bolting, welded joints, threaded joint, tubing joints, miscellaneous joints. Design requirement for specific systems refer to chapter II part 6 of B31.1 Design for sustained and occasional loads refer to chapter II part 2 para 104.8 of B 31.1 Design criteria for thermal expansion refer to para 104.8.2 chapter II part 2 of B31.1 Flexibility analysis as per appendix D of B31.1. Exemptions are provided in para 119.7.1 Supports and Restraints are covered under chapter II para 120, 121, 130, MSS SP-58

Materials Requirement: Material listed in Appendix A Material listed in a code case that permits it Material listed in a standard that is referenced in table 126.1 Component is flared, flareless or compression type tube fittings complying with para 115 Material non metallic as para 105.3, 124.8 Fabrication, Assembly & Erection : Chapter V of B31.1 covers rules for fabrication , assembly and erection. Includes requirement for welding, details for specific type of welded joint, preheat, heat treatment, bending and forming, brazing and soldering, assembly and erection. Welding process generally used are arc welding processes such as SMAW, GTAW, GMAW, FCAW, SAW. WPS, PQR, WPQ meeting ASME section IX requirements. Refer para 127.2, 127.3. Essential, non essential and supplementary variables are to be considered for welding qualifications. Preheating requirement to para 131 of B31.1 to be followed as a minimum. Minimum temperature for welding shall be 10deg C, exception for GTAW is given in para 131.5 where preheat temperature can be lower. For tack welds preheat zone to cover three inches or 1.5 times base material thickness. Heat treatment as para 132 of B31.1. Furnace heat treatment is preferred, local heat treatment is also permitted. Band three times maximum thickness of part being joined needs to be followed. Heat treatment requirement after bending or forming is given in para 129.3 Cold bending is considered when it is 56deg C below lower critical temperature otherwise above that it will be hot forming. Heat treatment requirement as per para 129 to be applied . PWHT as per para table 132 see para 132.4.2 Bolted joints : Refer para 135.3 of B31.1 and appendix S of section VIII div 1 Welded joints: Refer para 127.4.2, 127.4.4( B), ( C )

Examination: Table 136.4.1 gives type of non destructive examination t be carried out. All joints are to be visually inspected to visual standard given in 136.4.2 Pressure Testing : 1) 2) 3) 4)

Hydrostatic Testing Pneumatic testing Mass spectrometer and halide testing Initial service testing

As per PG 99 the hydrostatic pressure will be 1.5 times design pressure. Maximum stress during test is limited by para 102.3.3 ( B ) Leak test after PWHT , NDE, other fabrication, assembly and erection activities required by system. Pneumatic test to 25 psig permitted to locate major leaks. Certain cases pneumatic test can be substituted in place of hydro test in which case pressure need to be 1.25 times design pressure Retesting after repair or alterations as per PW 54-2 and PW 54-3 Non metallic piping use as per Para 105.3, 124.8 Stamping as per code requirement “ PP “ S stamp holder are authorized to make power piping as per B31.1.