×
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

overpresurization on sp 6071 vessel
2

overpresurization on sp 6071 vessel

overpresurization on sp 6071 vessel

(OP)
Hello everybody,

I had a pressure vessel DOT SP-6071 for hydrotest that was
accidentally was overpressurized to 1.6 timss hydrostatic test pressure. How will I determined if the unit is to be scrapped or got a chance to remain in service?

The vessel service pressure is 700 psi, its test pressure is 1800 psi and, yes, it was presurized to 2880 psi.
It was not possible to read permanent expansion since the sistem had a leak.

The vessel is manufactured with Almar-362 Stainless steel which specs are as follows;
Martesitic stainless steel
C0.05 max;Cr14-14.5;N 6.25-7; Ti 0.6-9; Bal fe
Annealed: 188.000 TS 182.000 YS; 13EL, 41HRC.

THe vessel did expand progresively without any drop in pressure.

Afterward a test with its normal test pressure was sucessfull.

I,ll welcome any insight in the matter.




 

RE: overpresurization on sp 6071 vessel

I cannot speak for DOT vessels but ASME vessels and pipes allow up to 90% of yield under the hydro loading. In your case I would perform the following.

1) Find your allowable stress under hydrostatic test.
2) Calculate the state of stress in the vessel for the 2880 psi you applied.
3) Compare calculated stress to your allowable, if you still pass you are all set.
4) If you fail, compare your calculated stress to material yields and ultimate strengths. Judging from your very poor tensile to yield ratio, the material is not ductile and any yielding will very severely degrade vessel integrity. (if I calculated yielding, I would scrap it but it depends on 5 below)
5) As far as judging the adequacy of a yielded vessel for service that will depend entirely on the rules you designed the vessel to. But I would venture to guess that yielding will be prohibited.
 

RE: overpresurization on sp 6071 vessel

(OP)
Thank you very much ColonelSanders83!

Now I think I can figure out how to calculate my allowable stress under hydrotest for this vessel but I am not very sure about(point 2)calculating the state of stress in the vessel in which 2880 psi were aplied.

I got to admit I am quite ignorant about this since my work usually only have to do with the simpler matters of testing the vessels and the enginer that could help is on holidays at the moment.

At his return he will take the matter but at present I am to seek answers.
Again Thank you for your reply.  

RE: overpresurization on sp 6071 vessel

f2t...if you can calculate (1), you can calculate (2).  Substitute actual test pressure for design test pressure and solve for stress.

RE: overpresurization on sp 6071 vessel

(OP)
Thank you for all your help! Thank you Ron, I just could not think.

I calculate my wall stress under normal hydrotest conditions and I have 84375psi.

The vessel was under 135000psi wall stress which is just 1.6 times the stress under test pressure.

The formula I was given states that wall stress equals test pressure times vessel diameter and the result to be divided by four times wall thickness.

These value seem far from tensile strengh and Yield values, but is there a way to test for damage( i.e.comparing hardness?). I do have another vessel that was tested properly.

Again, I will apreciatte any insight.


 

RE: overpresurization on sp 6071 vessel

The formula you were given only calculates axial stress in a cylinder wall. You also need to look at hoop stress which is pressure times diameter over two times the thickness. See here for a quick rundown on hoop and axial stress in a cylinder. http://en.wikipedia.org/wiki/Cylinder_stresses

You should make sure you also evaluate stresses at the tank penetrations. Penetrations involve discontinuities in the vessel shell and are generally associated with high stresses.

Realistically you will not be able to do much with the vessel until the engineer returns, because wile you can calculate the hoop and axial stresses in the cylinder you do not know what to compare the values to (should you compare to yield or only some fraction yield, this information will be in the design code used for the tank). But more importantly you do not have the tools to calculate stresses at the vessel penetrations (These are likely to be the most highly stressed locations in the vessel).

As far as testing for damage goes it will be difficult. An over pressurization of vessel will not affect hardness, only the strain in the steel and that is almost impossible to measure without a strain gage (or other such methods) recording strain while you were testing. You may be able to x-ray and look for cracks but that won't tell you how much the vessel has yielded.

Like I stated previously, if your vessel has yielded I would toss it. Your engineer may not, due to his more intimate knowledge of the vessel and its requirements (as stated before I work with ASME vessels and pipes)
 

RE: overpresurization on sp 6071 vessel

(OP)
Thank you again ColonelSanders83!

You are correct I can´t really do much about it without the engineer, he will find out what to do.

I know that this is relatively new to him, since he came to his position and kind of work just I a few months ago, but he does have the base knowlege and training I lack to make the correct decision.

I know some guys in my company do x-ray components and perform hardness testing, but I know nothing about strain gauges.

Also I wonder if in a waterjacket hydrostatic test the total expansion and permanent expansion ratio is a indication of if the vessel is staying still within its elastic deformation.

Thank you again!






 

RE: overpresurization on sp 6071 vessel

I am curious to know the outcome of this vessel. What has been done?

RE: overpresurization on sp 6071 vessel

(OP)
Hi COlonelSanders83,

I am sorry I have not anwser before but I was abroad and without access to a computer.

The vessel was made scrap and send to be destroyed as far as I know, last time I saw it was with a red tag and all markings removed in the expedition area.

I kind of knew that will be the outcome.

I will like to thank you, and Ron, for your valuable help.

 

I read somewhere that about 66.352 percent of all stadistics are just made up numbers!

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