×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

CTOD test on 5D Bends.

CTOD test on 5D Bends.

CTOD test on 5D Bends.

(OP)
For sub sea pipeline usually CTOD test is carried out for both pipeline and 5D bend used in the pipeline.Can any body suggest the exact reason of doing CTOD( Crack Tip Opening Displacment)test. Because for piping under ASME B 31.3 piping this test is generally not suggested by any consultant.   

RE: CTOD test on 5D Bends.

In your experience, does the CTOD testing you 'usually' come across also have stipulated acceptance criteria, or is it for information?  If the latter, it is to provide input into any engineering critical assessment (ECA) that may be performed later on.  If the former, it may be that the ECA has already been carried out.

Steve Jones
Materials & Corrosion Engineer
http://www.pdo.co.om/pdo/

RE: CTOD test on 5D Bends.

A 5D bend is most likley made by induction bending.  Done poorly, properties will degrade.

RE: CTOD test on 5D Bends.

OK - so what will a CTOD test tell us then?

Steve Jones
Materials & Corrosion Engineer
http://www.pdo.co.om/pdo/

RE: CTOD test on 5D Bends.

CTOD will tell us if the Induction Bend process has screwed up the toughness properties.  Charpy may also be used for this purpose.

RE: CTOD test on 5D Bends.

Precisely - so why CTOD test?

Steve Jones
Materials & Corrosion Engineer
http://www.pdo.co.om/pdo/

RE: CTOD test on 5D Bends.

The advantage of CTOD is that it provides a K1 value at slow loading rates.  A K1 value can be used for determining allowable flaw sizes where as charpy energy can do so only poorly.  If one also looks for a minimal amount of CTOD stretch zone formation, say 0.15mm, then it is likley the piece has good toughness against both slow and rapid fracture.

The charpy test is a better (as well as faster and less expensive) test when the upper shelf material toughness is less than 100J.  (Some might put this in the 100J to 200J range) Below 100J, the charpy test is a high strain test and indicates toughness pretty well.  Particularly as one should also have pre-bend charpy data to compare to.

When pre-bend toughness is over 100J, charpy energy may be miss leading if too much of the hammer energy is being consumed by crack initation.  In that case, the test is not measuring toughness against high strain rate and may result in a miss-leading high toughness value.  Even so, a high charpy energy value is still pretty good and acceptable for many applications.  Charpy is still the most commonly used standard.

In my opinion, CTOD should be reserved for critical applications where technology is being stretched in one way or another.  Standard applications that have been done many times before should stick with charpy.

RE: CTOD test on 5D Bends.

Thank you - we got there at last.  The only real value of performing CTOD testing is either to provide accept/reject information or to provide input into an ECA.  To provide accept/reject information, one must have an acceptance criterion or critera.  If there isn't one (or any), and an ECA is not going to be performed, then there is no point doing the CTOD test.

Steve Jones
Materials & Corrosion Engineer
http://www.pdo.co.om/pdo/

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources