Creep measurement

[MalcolmA]

I'm looking for advice on techniques to measure the amount of creep that has been sustained by a furnace tube.
Also, what is considered an acceptable amount of creep.
Are there any codes or standards that provide guidelines.

 

[btrueblood]

Ask this question in the boiler & pressure vessel forum.

 

[jte]

MalcolmA-

You need to get your hands on a copy of API Standard 530, "Calculation of Heater Tube Rhickness in Petroleum Refineries." Annex A, "Estimation of Remaining Tube Life" should be particularly useful.

btrueblood was right, you probably would get more responses from the B&PV forum.

jt

 

[bvi]

Do a search based on Omega methods. Small samples can be removed, and the extent of creep life exhaustion determined by a relatively short term creep test on the sample. There are a number of technical papers on this, and a MPC program that developed this technology.

 

[btrueblood]

Guys, Malcom re-posted his question into the B&PV forum and got a lot of helpful info. on the subject.

 

[briand2]

Malcolm,

Perhaps you're referring to the "Peaking" measurement for the longitudinal weld? (Nod, Nod, Wink, Wink).

Brian

 

[athomas236]

One way of measuring creep damage to tubes and pipes is replica testing.

This involves grinding, polishing and etching part of a tube and/or weld to a mirror finish. The area is then coated with acetone and a plastic film placed over the prepared surface. After drying the plastic film (which now has a replica of the grain structure) is removed and examined under a microscope. The examination will allow the creep damage to be placed into one of eight categories. VGB standard TW507(1997) has eight such categories and provides guidelines for classification of creep damage.


athomas236

 

[MalcolmA]

Thanks to everyone for the advise.

briand2,
I'm not sure what is meant by "Peaking" measurement.

 

[briand2]

Malcolm,

1. I thought you were a different "MalcolmA"...sorry.

2. "Peaking" measurement is what's done on fire-tube / shell boilers (here in the UK). It measures the extent to which the longitudinal weld on the shell protrudes radially outwards from the surrounding shell. Over time, this measurement increases (it's measured with a simple gauge) due to cyclic operation.

Regards,

Brian

 

[athomas236]

Thats interesting I never realised that firetube/shell boilers could be subject to creep. I always thought that they operate at such low pressures and temperatures the design was not based on time limeted stresses.

athomas236

 

[Daytona955i]

Malcolm

Be aware that peeking has got diddly squat to do with creep.

It is to do with poor quality manufacture resulting in a "peek" or flats either side of the long seam of a fabricate cylinder. This out of roundness induces a Moment in addition to the stress field normally expected in a cylindrical shell.

This was a major problem in the late 80's / early 90's here in the UK, specifically with the shell of Fire Tube (also known as "Shell" or "Package") Boilers which resulted in a number of catastrophic failures. The problem was addressed by a SAFed (Safety Assessment Federation) committee who have derived a methodology of addressing this problem.

As always, a little bit of knowledge can be a dangerous thing!