Evaluator
Specifier/Regulator
- Feb 23, 2007
- 1
This standard lists qualification tests (two times the rated valve CWP pressure) for needle valves to establish the CWP of the valve,it also requires a "burst test". Pargraph 5.6.2 states "leakage is permitted at the valve packing gaskets and pressure retaining joints during the burst tests at pressures above the proof pressure. 5.6.3 states if the hydrostatic test is stopped before rupture occurs,the highest sustained pressure attained shall be considered the burst pressure.
The equation to satisfy is .....
CWP is less than than or equal to 0.25 x Burst Pressure x Tensile min divided by tensile actual.
The burst pressure required for CWP of 10,000 PSI needle valve made of ASTM A276 316 stainless steel far exceeds the pressure of the valve packing or metal seals of the valve and the NPT threads. Any modification to NPT pipe threads changes the design of the valve, the metal to metal seats on the valve bonnets and packing have been tested to 23000 PSI,(two times the rated pressure) further hydrostatic pressure is not possible to satisfy the equation.
We have considered welding the bonnets to the valve body and welding high pressure tube to the inlet and outlet of the valve using high pressure autoclave fittings. This may work on stainless steel, however the standard allows the use of ASTM A108 carbon steel,in this case any welding would destroy the mechanical properties of the Astm A108.
I see competitors literature complying with this standard and list A108 valves meeting this standard. I am at a loss as to how this was accomplished. I am desparate for answers,can anyone help me?
The equation to satisfy is .....
CWP is less than than or equal to 0.25 x Burst Pressure x Tensile min divided by tensile actual.
The burst pressure required for CWP of 10,000 PSI needle valve made of ASTM A276 316 stainless steel far exceeds the pressure of the valve packing or metal seals of the valve and the NPT threads. Any modification to NPT pipe threads changes the design of the valve, the metal to metal seats on the valve bonnets and packing have been tested to 23000 PSI,(two times the rated pressure) further hydrostatic pressure is not possible to satisfy the equation.
We have considered welding the bonnets to the valve body and welding high pressure tube to the inlet and outlet of the valve using high pressure autoclave fittings. This may work on stainless steel, however the standard allows the use of ASTM A108 carbon steel,in this case any welding would destroy the mechanical properties of the Astm A108.
I see competitors literature complying with this standard and list A108 valves meeting this standard. I am at a loss as to how this was accomplished. I am desparate for answers,can anyone help me?
