304 / 304L. 304 is the original "18-8" stainless. It is produced in greater quantity than any other austenitic stainless steel. 304 provides useful resistance to corrosion in many environments ranging from moderately reducing to moderately oxidizing. Through the controlled addition of nitrogen, it is common for 304L to meet the mechanical 304 L Stainless Steel Strip for Manufacturing - UNS S30403 Since 304L is an extra low-carbon variation of 304 it can often be used in the "as-welded" condition (without annealing), even in severe corrosive conditions, except for applications specifying stress relief. 304L has good welding characteristics and can be welded by all standard methods but attention needs to be paid to avoid weld "hot cracking".
The Type 302, 304, 304L and 305 alloys are the most susceptible of the austenitic stainless steels to stress corrosion cracking in halides because of their relatively low nickel content. Conditions which cause stress corrosion cracking are:(1) presence of halide ions (generally chloride), (2) residual tensile stresses, and (3) temperatures in excess of about 120°F (49°C). ASTM A312 Stainless Steel Pipe SpecificationASTM A312 Stainless Steel Pipe Specification Standard Specification for Seamless, Welded, and Heavily Cold Worked Austenitic Stainless Steel Pipes ASTM A312 pipe is common use stainless pipe for industries. It covers diameters from 1/8 to 30 and thickness from SCH 10S to SCH 80S. General use material grades are TP304/304L, TP316/316L. ASTM A778 Stainless Steel Welded Tubes ASME SA 778 The ASTM A778-304l is one of the most used materials. It is a low carbon variation of the 18/8 chromium nickel stainless steel. The chromium nickel composition provides better corrosion resistance and strength while the less carbon content provides ductility and better welding properties. the ASTM A778 tp316l is a low carbon version of the 316
Stress relieving.CS 304L can be stress relieved at 450-600 o C for one hour with little danger of sensitisation. A lower stress relieving temperature of 400 o C maximum must be used. 3. Hot working Initial forging and pressing:1150to 1260 o C Process Pipes - Temperature and Allowable StressFor B31.3 Process piping, allowable stress is tensile strength at temperature divided by 3. Note! for B31.1 - Power piping, allowable stress is tensile strength at temperature divided with 3.5. Pressure Ratings - Pressure ratings of pipes and tubes and their fittings - carbon steel , stainless steel, plastic, copper and more. Technical Data BLUE SHEET - METSERVE348 stainless steels offer higher creep and stress rupture properties than Type 304 and, particularly, Type 304L which might also be considered for exposures where sensitization and intergranular corrosion are concerns. This results in higher elevated temperature allowable stresses
The stress values in this range exceed 66 2/3 % but do not exceed 90% of the yield strength at temperature. Use of these stresses may result in dimensional changes due to permanent strain.