Stainless Steel Pressure Vessels should comply with additional requirements specified herein, in addition to “Specification - Pressure Vessels”.
Stainless steel heads and transition sections which have been cold formed should be solution annealed and then cold sized to correct for distortion, if any, prior to welding to the shell.
Stainless steel materials with strength enhanced by cold work should not be allowed. Stainless steel bolts should have machined heads and threads; rolled threads should not be acceptable.
The allowable design stress for stainless steel vessels should not exceed two-thirds (2/3) of the yield strength at the design temperature, unless a higher allowable design stress is approved in writing by Buyer.
When post-weld heat treatment is specified for stainless steel vessels, all welds and cold formed parts should be thermally stress relieved at 1550°F (843°C) to 1600°F (871°C) for one (1) hour per inch of thickness, with a one (1) hour minimum, and then properly air cooled.
Chemical analysis should be performed on deposited weld metal for each lot of stainless steel welding consumables.
- This should be performed either on test plates, or from sample drillings of production welds.
- Analysis should meet the requirements of ASME SFA 5.4 of the grade of stainless steel specified.
Stainless steel base metal and weld metal should be cleaned so as to provide the maximum corrosion resistance.
Supplier should provide, prior to the start of fabrication, the proposed cleaning procedure to Buyer for review and approval.
The ferrite content of all Code Category A, B, C, and D stainless steel weld joints should be determined on both surfaces of each finished weld before any post-weld heat treatment.
Ferrite content should be determined using a magnetic instrument calibrated according to AWS A4.2 standard procedure, and should be between 3FN and 10FN.
All ferrite measurements should be recorded, along with the accurate location of each measurement.
6. Hydrostatic Pressure Testing
Test fluid for solid austenitic stainless steel or cladded vessels should not contain more than 100 ppm Chloride content.