Stainless Steel Fittings – Heavy Pattern vs Light Pattern
Stainless steel fittings were originally manufactured to the same dimensions and wall thicknesses as iron fittings and the ANSI B16.3 standard. Later the MSS SP-114 standard was written for Class 150 stainless steel fittings, which was based on ANSI B16.3 dimensions. Today there are serval different patterns that vary in dimensions, wall thickness and weight. Stainless steel fittings to MSS SP-114 specification are to be used when ASME B31 piping code is required. When compared it is easy to see that the lighter pattern fittings are not the same in quality and should be used in limited applications since they do not fully comply with ASTM A351.
This table summarises the differences between the standards:
|Heavy Pattern MSS-SP-114||Light Pattern|
|Rating||Class 150||150 PSI|
|Applications||Industrial Processes||Residential and non-critical plumbing|
|Material Grades||Available in 304 and 316||Available in 304 and 316|
|Dimensions||Heavy duty wall thickness and larger diameter||Significantly less material with thinner wall|
|Benefit / Value||Long lasting, better erosion protection||Costs less|
|Temp (⁰F)||Class 150
|-20 to 150||300|
The pressure rating for the MSS SP fittings is 300 psi @ 150 ⁰F and is identical to class 150 malleable fittings. As the process temperature increases, the pressure rating decreases.
Note: (a) Permissible for service temperature up to 366 ⁰F, reflecting the temperature of saturated steam at 150 psig.
Organizations & Standards
- ASTM – American Society for Testing and Materials
- ANSI – American National Standards Institute
- ISO – International Organization for Standardization
- MSS – Manufacturers Standardization Society
- Further built upon the standards written by ASTM, ANSI, and ISO with more detailed requirements.
- ASME – American Society of Mechanical Engineers
- Standards are derived and compiled from the standards released by all four organizations.
- CRN – Canadian Registration Number
- ANSI / ASME B1.20.1 – defines the thread dimensions and tolerances.