Yield to Tensile Ratio

[zebmahar]

Hello Guys!

We are producing 10" x 11.7 x DRL Seamless pipe in API 5L Gr. X 60, with material composition as follow:-

C = 0.14 %, Si = 0.22 %, Mn = 1.33 %, P = 0.0012 %, S = 0.00062 %, Cr = 0.165 %, Ni = 0.143 %, Mo = 0.022 %, Al = 0.0241 %, Cu = 0.215 %, Co = 0.0107 %, Ti = 0.0016 %, V = 0.00034 %, W = 0.0071 %, Pb = 0.0010 %, Sn = 0.0109 %, Ca = 0.0010 %, Fe = 97.7 %, CE = 0.42%

I want to know, what is the procedure of reducing the yield to tensile ratio? In our case the ratio is 0.93 which is within the limits of API 5L Gr. X-60 but the customer has specified 0.87. We have changed the heat treatment parameters 2 to 3 times in the following range

Required: Yield = 415 – 565,Tensile = 520 – 760, Ratio = 0.87

Temp (C) Time(Mints)Yield Tensile Ratio

675 12 586 602 0.97
675 15 575 595 0.96
725 20 480 504 0.95

But the yield and tensile is reducing with the same proportion, hence the ratio is same. Please advise what we should do to reduce the ratio.


Kind Regards
Zebmahar

 

[salmon2]

This seeks like a hsla steel with this chemisty the ratio will be always high unless you only normalize it and are satisfied with low yield. To me you have to change chemisty, a richer chemisty, which gives you larger room between yield and tensile usually.

 

[metengr]

Go back and discuss this with the customer. If the YS/TS ratio is within API limits and the customer requires a lower ratio, you will probably require an alternative chemistry to provide for lower YS, by increasing grain size. The current microalloy elements are grain refiners.

 

[SJones]

Is the pipe for H2S service and what are the Charpy toughness requirements? If it is yes and high, then you will have virtually no chance of meeting 0.87, a figure which hearkens back the early 90s for SAW pipe - a completely different animal. You may just wish to ask the reasoning behind 0.87 for seamless pipe. The tighter restriction for SAW was down the Bauschinger effect that will not be apparent in seamless pipe.

Steve Jones
Materials & Corrosion Engineer

http://www.linkedin.com/pub/8/83b/b04

 

[zebmahar]

This pipe is for H2S services and the impact requirements are 48 j average absorbed evergy at -23 C