Welding Tips and Tricks

Hi there, I am a pipe welder and am wondering if anybody knows the numerical classification of 9 chrome pipe. I am aware of its piping applications and "runny" welding characteristics but nobody can tell me anything about it other than its 9% chrome, and Im not sure thats even accurate. Its probably like .9% chrome. Thanks in advance Adam

I'm gonna take a stab and say that you are probably referring to P91 pipe or P(T)91. It is a chromium-molybdenum pipe and tube. 9CrMoV. It is a creep strength-enhanced ferritic steel (CSEF) used primarily for strength or enhanced corrosion resistance at elevated temperatures. A213 T91 (seamless tube), A335 P91 (seamless pipe). Is that maybe what you are talking about? It is also 8.00 - 9.50 % chrome.


Jim

yea, thanks, that does sound like what im talking about. however what is a creep strength enhanced ferritic steel. Thanks for your previous response. Adam

Strength and creep properties
The design stress for a material specifies the load to which it can be subjected at high temperatures without failing or being significantly deformed during service.

From room temperature up to a certain temperature (550 - 600 °C for most austenitic steels), the design stresses are based on the proof strength of the material. Above that temperature, the more temperature dependent creep strength will determine the design stress values. As a rule, creep strength is expressed as the creep rupture strength, i.e. the stress that causes rupture after 10 000 or 100 000 hours (Rkm 10 000 and Rkm 100 000). For components that are more sensitive to deformation, the creep deformation strength, i.e. the stress resulting in a strain of 1% after 10 000 or 100 000 hours (RA1/10 000 and RA1/100 000), should be used as a basis for design calculations.

An often-neglected mechanical property is the ductility. In a creeping component, stress redistribution due to creep can off-load the heaviest stressed parts, provided the ductility is high enough. Moreover, the resistance to low cycle fatigue (during start-ups and shut-downs, or major service transients) is proportional to the ductility.

The MA alloys have higher proof strength values at room temperature as well as at elevated temperatures. This is mainly a result of the higher nitrogen (and carbon for 253 MA) contents in these two alloys.

The higher nitrogen content is also the main reason for the MA alloys' higher creep strength - a strength that does not decrease so rapidly with increasing temperature as it does for common HT alloys.