Wall Thickness Estimation in Pipes 2

[mechiit]

My question is, how to estimate the wall thickness of SS pipes with He gas flowing in it at conditions of 950 C and 70 bar pressure.

I found that SS310S or 253 MA steels can withstand such high temperatures and pressures. I understand that the design criteria is the creep strength and not the yield strength because of higher temperatures involved. Is there any formula or method to estimate the wall thickness for gases flowing in pipes and which gives a conservative estimate at such high temp and pre

 

[metengr]

mechiit;
You don't estimate wall thickness, you calculate it. I would strongly suggest that you use a recognized boiler/pressure vessel design standard, like ASME Boiler and Pressure Vessel Code. Determination of wall thickness for high temperature and pressure service conditions is not as simple as using Barlow's formula for hoop stress, and using high temperature properties. Yes, creep deformation will be the governing factor in determining wall thickness, and using a recognized pressure vessel code with appropriate material selection and formula's with suitable design margins will keep you safe.

For this type of operating pressure and temperature, you need to select a high temperature, heat resistant alloy that is Ni-base, with Co and Cr and Mo additions (UNS 06617), which has allowable stress values up to 1800 deg F. Most heat resistant stainless steels used in pressure vessel and piping design are only good to 1550 deg F (upper limit).

If you can access ASME Section II, Part D and Section VIII, Div 1 these sources will contain all of the necessary information to allow you to determine the required wall thickness.

I presume that these pipes are part of a vessel? Can you elaborate on this?

 

[metengr]

In reviewing ASME Section II, Part D, another choice is

ASME SB 407 UNS NO8810, small tube and pipe, max temp permitted is 1800 deg F

 

[mechiit]

Hi metengr;

Thanks for the info and for suggesting high temp materials.

The pipe is not part of any vessel. As a matter of fact it is a single pipe carrying He gas at such high temperature and pressure. Let me rephrase the entire question

He gas at 950 C and 70 bar (max conditions) will flow in the pipe. The pipe as such is not part of any vessel. The objective is to come up with the pipe dimensions for the maximum conditions (based on max mass flow rate, density at 950 C and taking max vel of gas as 25 m/s). (The pipe inside dia can thus be approximately found from the formula
m = rho * area * vel). Since the temperatures involved are high (and pressure is also high), the creep strength (instead of the yield strength) becomes the design strength in the wall thickness calculation. I am looking for the design methodology for calculating the wall thickness required to withstand such high temperatures at such high pressure (70 bar). As u suggested I will look into ASME Section II, Part D and Section VIII, Div 1 and try to figure out the design methdology for calculating wall thickness. A met.engr from RA suggested me that RA 253 MA can withstand such high temperatures and I found that it has a very good creep strength at such high temperatures (almost twice of 310 S at elevated temperatures). Pls add your comments if you have any additional information

 

[EdStainless]

Your pipe is part of a pressure system, therefore you should use a pressure code to guide the design. That is what the Boiler and Pressure Vessel Code is.
You need to rely on published creep strength limits. This is a dangerous application. You need enough safety margin.
If the B&PV Code does not have creep data for the temp that you want then look for another alloy.

= = = = = = = = = = = = = = = = = = = =
Rust never sleeps
Neither should your protection

http://www.trent-tube.com/contact/Tech_Assist.cfm

 

[mechiit]

Hi,

Kindly read the previous posts (for more details) if you find the details given below are not sufficient

I have a question on Lame' Equation for evaluating the wall thickness of the pipe. I borrowed this equation from process piping ASME B 31.3-1999 edition [Page number 20, equation (3c)]. Lame' equation is given by,

t = (D/2) * [1 - sqrt{(SE-P)/(SE+P)}] where t is pressure design thickness, D is the outside diameter of pipe, S is the allowable stress, E is the quality factor and is 1 for seamless pipe, P is the internal design gage pressure. Since the temperature involved in my case is high (950 C), the creep rupture strength becomes the allowable stress

My conditions are as follows :
a) P is 70 bar or 7 MPa, Temperature is 950 C (~1800 F), E=1 (seamless pipe), D can be taken as 33.4 mm

b) The value of S at 950 C for the materials I am planning to use is less than P and hence the term inside the square root(in Lame' equation) becomes negative which is absurd.

So, can I use the Lame' equation for evaluating my wall thickness or is there any other procedure involved for such high temperature cases. Other equations given in the ASME code for evaluating wall thicknes are giving me agreeable numbers but Lame' equation is giving me absurd result at such high temperatures.

Kindly let me know if there is any other method for such high temperature cases (or) let me know any possible mistake that I could have done in evaluating the wall thickness.

Thanks

 

[metengr]

Why would you use Lame's equation, which is applicable for thick-walled cylinders? There is no provision in Lame's equation for creep stress re-distribution, as with the equations listed in ASME B&PV Code.

What material and value are you using for allowable stress? You will have to increase wall thickness of the pipe until the allowable stress is > than internal pressure.

 

[mechiit]

I am using two materials, alloy 617 and alloy 253 MA and comparing them to arrive at the suitable material. The values are as below:
For Alloy 617 : @ 1800 F the allowable design stress is 5.03 MPa (0.73 ksi). (value taken from page no 8, table 8 from the technical manual [for Inconel alloy 617] availaible on the website specialmetals.com)
For 253 MA : @ 1800 F, 6.14 MPa (o.89 ksi). This value is the average stress for min. creep rate of 0.0001%/hr [value taken Table 4, page no 3 from the technical manual for 253 MA availaible on rolled alloys website).

when you say ASME B&PV code did you mean ASME B 31.3 ( as I took the equations from ASME B 31.3). If not , pls let me know on section or what para no. the equations are listed in ASME B & PV code.

The other equations that I used are (these gave me meaningful results) :
t = PD/(2(SE+PY)) (eqn 3a from 304.1.2 of ASME B 31.3)
for Ally 617 : I used Y = 0.4
for 253 MA : I used Y = 0.7 (Y values taken from Table 304.1.1 from ASME B 31.3)

In your reply to my question you said :
"You will have to increase wall thickness of the pipe until the allowable stress is > than internal pressure"
The allowable design stress for a material is the limit based on temperature. I plug this into the equation and calculate my wall thickness. So I did not understand what it means by increasing the wall thickness until allowable stress is > internal pressure.

I used Lame' equation since I thought that my wall thickness will be high enough (t/D > 6) because of the pressure and temperatures that I am looking for.

Thanks

 

[MJCronin]

mech...

Am I missing something here or are you trying to get SS to work at 950C (~1800F) ?????????

There is NO strength left for any commercially available SS at that extreme temperature.

The ASME B31.1 codes and ASME Section I end thier allowable stress levels at ~ 1400-1500F

Good luck

-MJC

 

[rolledalloy]

RA 253 MA is only approved by the ASME boiler and pressure vessel code to 1650F (900C)at that temperature the allowable stress value for plate is only 710 psi. Note this is lower than the strength criteria you are using at 1800F. 617 is much stronger than RA 253 MA at these temperatures.

Like the other posts, I would suggest you use an alloy approved for use to 1800F by ASME. Besides 617, Haynes 230 (UNS N06230) and RA 602 CA (UNS N06025) are approved to this temperature. Getting true pipe will not be easy in any of these grades.

 

[mechiit]

can any one help me out with the ASME allowable stresses (for seamless pipe/tube) for Alloy HR160 (UNS N12160) from 1550 F to 1800 F. I guess they are availaible in the 2004 ASME B&PV Code Section II. I could not get hold of this book. I will appreciate if anyone can post them for me. Thanks in advance

 

[metengr]

ASME SB 622

Per the 2004 ASME B&PV Code, Section II, Part D, this material is permitted to only 1500 deg F.

 

[mechiit]

Hi
Thanks for the info. I had talked with a Haynes intnl rep. and he told me that it is approved recently by ASME up to 1800 F. I thought that the data will be availaible in 2004. I am not aware if there is a newer version of code than 2004.

 

[metengr]

mechiit;
I checked the 2006 addendum of the 2004 Edition of Section II, Part D, Table 2 and there is no revision to the maximum permitted service temperature of 1500 deg F.

It might have been a code case that was recently adopted. I will check on this.

 

[metengr]

Yes, indeed it is a code case

CC 2385-1
I would recommend you review this code case for specific requirements. Here are the stress values which apply to specific product forms (SB-622 seamless pipe and tube, and others);

1550 deg F 1.8 Ksi
1600 1.5
1650 1.3
1700 1.0
1750 0.85
1800 0.73

Subsection C and Part UNF rules apply. Welding is limited to GTAW and GMAW processes.

 

[mechiit]

Hi metengr

Thanks for the info