Maximum Heating Rate of Carbon Steel?

[dsring]

Can anyone tell me if there is a maximum recommended temperature rate of change (heating rate) of 2-inch, Schedule 80, SA106 Carbon Steel pipe? I am heating the pipe from 120 deg F to about 490 deg F in approximately 5 minutes. Will this rapid heating rate cause any problems in the pipe?

 

[Wolfpack51]

I cant find anything that would prohibit, or cause damage to a rapid heating of A106 steel. In your range you have not formed a phase change in the metal. And 5 min. is not real rapid considering the material. Your primary concern will be rate of cooling after welding, depending on the enviroment ( very cold ), rapid cooling can cause several problems.

Good luck.

TMC

 

[sayee1]

The maximum temperature you have specified is 490 F which is ~255C. For temperatures below 800 F, the heating rate and cooling rates do not have a significant affect on the material properties. That is why even for PWHT as per UCS 56, ASME Sec VIII div 1, the temperature above which the heating rates and cooling rates specified is 800F. However why are you concerned? The heating rate is pecified to ensure that the component gets uniformly heated up and ythere is no temperature gradient set up across the thickness of the component which may lead to thermal stresses. Your case the thickness is less than 1/2" and I would not think that the heating rate within the range of temperature specified should cause any problem.

Thanks and regards
Sayee Prasad R
End of all knowledge is the attainment of immortality!

 

[Koz]

Hi Folks,
So I know ASME allows rapid cooling below 800 F. Production schedules require us to MT a 300,000 lb vessel (Pl. 2&quot, A516 gr 70 after stress relief. Can I spray water on it to get it down to 100 F quicker? A local heat treater says I can at 300 F and lower. Another has said 600 F and lower. Why those "magic" numbers and not 800 F?

I hear a lot about the preheat required for carbon steel. Is there a recommended quench rate? Why is it sufficient to bring, say, A572 gr 50 Pl. 1-1/2" to 150 F (AWS D1.1)and weld with SAW (slow quench through 1400 F to 900 F) or SMAW (quicker quench). Why is it preheat at all rather than rate of cooling through the transition temperatures?

For CVN tougher welds in mild steels, I have found it more important to control the interpass temperatures than the preheat or even cycling of preheat. My mechanical values have never been below specification limits without preheat and we have spent $$ to show this to inspectors. This data is not statistical, just tests we've run over the years. But I understand Japan is currently building bridges without preheat. I am strictly talking mild steels with YS 70 ksi and lower. But why aren't we concerned with the rate of quench during welding and heat straightening. It seems to me a change of about 80 F from ambient would make very little difference concerning a temperature gradient up to approx 2700 F. And I won't talk about actual preheating methods found in production or in the field.

Koz

 

[Metalguy]

For carbon and low alloy steels, the *metallurgical* temp. of interest during cooling is right around 1200 deg F. That's where the hi-temp. microstructure (austenite) will transform via diffusion to pearlite the fastest. *If* it manages to cool below about 1000 deg. without transforming (which may take only a few seconds at 1200), then you will likely form bainite or martensite. While these microstructures have very desireable properties for some uses, relatively soft pearlite is usually preferred for other applications.

Therefore it is the difference between the preheat temp. and 1200-1300 that counts.

Your drop in impact values with high interpass temps. is probably because coarse (higher temp.) pearlite formed instead of the preferred fine pearlite (lower-temp. formation).