P91 material

[qualitypro]

Should the hydrotest medium(demineralized water)need to be maintained at any minimum temperature while pressure testing P91 piping systems although ASME B31.1 code does not specify so?

 

[davefitz]

ASME requires a min hydrotest temp of 70F, but for P91 one should ensure first that the welds were PWHT'd at or above 750 C , or ensure the hardness in the HAZ is within the acceptable range to ensure the toughness of the weld metal is adequate for hydrotest.

per Mannesman Valloured the followign impact energies are associated with different PWHT temps and hold times:

PWHT temp for time= impact energy @ hydrotest temp
730 C for 2h= 35 J@ 20C
730 C for 5 hr=55 J @ 20 C
750 C for 2 h = 55 J @ 20 C
750 C for 5 h= 81 J @ 20 C

 

[LAMAN75]

Assuming your dealing with boiler external piping: ASME B31.1 (137.1.2)"The temperature of the test medium shall be that of the available source unless otherwise specified by the owner"..... Although B31.1 has this statement a few paragraphs later the code states (137.3.1) " Boiler external piping shall be hydrostatically tested in accordance with PG-99 Section 1 of the ASME Boiler and Pressure Vessel Code"..... When you go to Sec 1 you will find the statements giving minimum and maximum water and metal temperature (PG-99) " pressure test using water at no less than ambient temperature, but in no case less than 70f"....... Also metal temperature ( PG-99.2) "The metal temperature shall not exeed 120f during close examination"..... As far as the demineralized water issue is concerned B31.1 (137.4.4) "Water shall be used as the test medium unless otherwise specified by the owner. Test water shall be clean and shall be of such quality as to minimize corrosion of the materials in the piping system".

 

[bvi]

The piping codes do not really deal with brittle fracture aspects related to low temperature pressure tests, other than by mention. You could look to Section VIII, Div 1 for guidance, UG-99(h), which recommends that the metal temperature during hydrostaticc test be at least 30F above the minimum design metal temperature, but not greater than 120F. B31.1 does not provide minimum design metal temperature, but you could get that from B31.3 or Section VIII, Div 1.