Pressure Vessel Bulge Assessment

[corus]

A bulge has formed in a pressure vessel wall under circumstances which are known, but are unlikely to happen again. Is there a method by which it can be determined if the area of the bulge needs to be replaced? I've seen out of roundness tests in pressure vessel codes before, but how do you treat out of flatness (in the axial direction of the vessel)?

corus

 

[unclesyd]

Can you provide a little better description of your vessel along with some sizes?

 

[corus]

The vessel is cylindrical (or was).

I'm not interested in the method of replacing part of the vessel wall, and hence size or whatever isn't relevant, but whether there is a need to make any changes at all when considering pressure vessel design codes now that the vessel is no longer cylindrical either in the circumferential or axial direction .

corus

 

[JoeTank]

I believe that API-579 (Fitness for Service) provides such evaluations.

Joe Tank

 

[metengr]

The pressure vessel design codes really don't apply to in-service evaluations. This is the reason for in-service Codes like the national Board Inspection Code or API 579.

First off, finite element analysis (FEA) or modeling could be used to determine how the bulged region is affected by service stresses. Once this is known, what type of future inspection (either nondestructive or other method) needs to be performed on the bulged area and surrounding vessel material on a periodic basis to assure continued safe operation.

 

[flamby]

Since the section is no longer circular, at some place the diameter (or better long axis) is more than what it was nominally. The stresses will go up in proportion to (long axis)/(nominal dia) as a rough check.

Ciao.

 

[deanc]

corus:

You are trying for a "use as is" so suggest you contact your Local Jurisdiction and Insurance Carrier before you proceed.

May be a waste of time to recalc.

I have pushed bulges back into place and done flush/window patches. But,why did this happen, have you cut coupons to check for material damage, have you contacted a "R" repair firm?

Think you better do some of this first.

 

[jte]

API-579 / ASME FFS-1 2007 certainly covers bulges. I've performed FFS for several shell bulges over the years. Excerpts from part 8:

The procedures in this part can be used to assess weld misalignments and shell distortions in components made up of flat plates; cylindrical, conical, and spherical shells; and formed heads. The types of flaws referred to as weld misalignment and shell distortion in this part are defined in the following paragraphs.

Bulge – An outward deviation of a cross-section of a shell member from an ideal geometry that can be characterized by local radii and angular extent. The local bulge geometry may be either spherical or cylindrical. Flat spots (infinite radius of curvature) are not considered to be bulges; they are classified as general shell distortions. If the bulge occurs at a blister, the analysis procedures in Part 7 should be utilized for the assessment.

If you choose to take the FFS approach, be sure to deal with an engineer experienced with FFS evaluations - these can be quite different from new design. And as deanc pointed out, check with the jurisdiction and insurance folks. The interest/involvement of jurisdictions in FFS varies quite a bit. Depending on what jurisdiction a vessel is in some of my FFS work may be reviewed and accepted by the State PV folks or they may have no interest in it.

jt

 

[MJCronin]

corus...

Well, one more time, lets begin the guessing game...

Was the vessel subject to temperatures or pressures in excess of design ? If so how high ?

Is this a carbon steel column in petrochemical Amine service ? (There is a long history here....) Has the vessel been repaired before and did the bulge occur in the area of repair ? Do you have any records at all regarding this vessel ?

Does the component have an ASME or equivalent stamp ?

Is the vessel protected by a safety relief device ?

-MJC