Impact test of 750oF C.S., UG-20(f)

[AMenJr]

Hey folks, need your opinion again. Part of my 1950 vessel has a 750oF design temp. I am installing SA516-70 & SA105 mat'l in this section. The 1950 ASME Code doesn't req. impact test or hardness limits. The 2004 Code, under UG-20(f) does. I believe it's due to the "creep-rupture range of C.S. at about 700oF" mentioned in API 510. We are allowed to design to the 1950 Code and NOT require impact test. I am recommending normalized, impact tested and limiting the hardness to 200BHN for adding our material to this section. One of the openings being added is a new 60"OD inlet and is a significant part of this section. Do you think I am being to Code critical by recommending these special material conditions, based on today's Code rather than the 1950 Code? I feel, better safe than sorry, especially since the added small cost of these test and conditions is not an issue.

 

[metengr]

AMenJr;
I believe you are fine specifying the material and heat treatment condition. However, if this vessel is an unfired pressure vessel this sounds like an alteration, and you need to be sure that it is performed in accordance with a recognized repair code standard (like the National Board Inspection Code or API).

 

[metengr]

The 1950 ASME Code doesn't req. impact test or hardness limits. The 2004 Code, under UG-20(f) does. I believe it's due to the "creep-rupture range of C.S. at about 700oF" mentioned in API 510.

Just one correction to part of the OP above, the requirement for impact testing has to do with the minimum design metal temperature (MDMT) and not exposure of carbon steel to 750 deg F. The requirement for impact testing is based on the vessel's original MDMT, which probably was not stated on the nameplate.

 

[AMenJr]

Thanks metengr, 1. so am I correct in stating that the 2005 Code requires impact testing, per UG-20(f), for these materials with a design temperature of 750oF? 2. Am I overkilling by requiring the material to be normalized and meet a max. of 200BHN?

 

[metengr]

AMenJr;

1. so am I correct in stating that the 2005 Code requires impact testing, per UG-20(f), for these materials with a design temperature of 750oF?

No. The impact requirements are related to the minimum design metal temperature. You are using UG-20 (f) in the wrong context. You need to follow thru and review UG-84 followed by UCS-66.

Next, having a normalized and tempered steel plate with a maximum specified hardness might be above minimum requirements. What is the function of the vessel?

 

[AMenJr]

metengr,
Sorry about the delay. The vessel is a vert. Fractionator tower 20'ID x 103's/s x 28psig. The bottom has a cone and the top has an elliptical head. The cone and 50' of the bottom shell is lined with 0.10"ss and operates at 700oF, designed for 750oF. Most of the vessel is about 1/2" thick with the section above the lining at 1/4" corrosion allowance and designed for 650oF. We are the owners agent and the owner requires us to do the calculations before the Coded shop does theirs. We are working close together with the shop so we have continuity and avoid ommissions and/or errors. The rest of the tower temperature drops as the fluid rises to the top of the tower with a final temperature of 281oF. We are adding numerous connections and re-rating the pressure of the vessel. All the internals are being replaced also to the latest technology. After reviewing you last comment, we regrouped with the team engineers and some of us took your view while others still held on to the belief that somehow UG-20(f) applies to the 750oF case. However, we were not able to prove how it applies or how it does not apply. The Owner takes the path that it does not apply. Well, to get to the meat of the question, we are still concerned about the 56 year old vessel section operating at 700oF. We make reference to NBIC RB-9100 (b)(3) which states "The lower temperature limit for the creep range for carbon steel is at least 700oF." We have expressed our opinion that the material should be tested for creep during the vessel alteration and the results included in predicting the service life left of the vessel. We also believe they should allow a metallurgist to review the material for this vesssel. Personally, I don't think they will, even though some of us believe it would be the safe thing to do. We have not seen anything that states we do not have to check the existing material stated above for creep after 56 years of service at 700oF. If you know of a published document that would help with this old material concerning this subject, it would be appreciated. I would go to the library here and look it up. Well, metengr thanks again for your comments. I really like the Engtips site forum.

 

[metengr]

AMenJr;
Creep deformation and fracture behavior as related to impact testing requirements in ASME Section VIII, Div 1 UG-20(f) are totally different damage mechanisms and design concerns. Thanks for the detailed explanation, now I see why you posted.

Ok, back to the issue at hand. If you have a concern related to creep life of this material, I can tell you that carbon steel at 700 deg F will show little, if any, loss in creep rupture life provided the service stresses have been at or below the allowable stress values referenced in ASME Section II, Part D.

What I would do in your position is to perform thickness testing to assure that you are at or above the minimum design wall thickness. The reason I would do this wall thickness survey is to assure that current stress levels are at or below allowable stress values in accordance with original design.

As a minimum, I would perform some surface nondestructive testing of any girth and seam welds. I would not conduct any creep testing UNLESS the wall thickness survey implies wall loss that would increase service stresses OR a review of the past operating/maintenance history indicates the pressure vessel has been exposed to repeated over-design temperature excursions. If you suspect over temperature excursions, you can have surface replications obtained of the carbon steel vessel material to evaluate the extent of spheroidization damage.

In my involvement with "aged" vessels, carbon steel can last many years if it has been installed in properly designed and operated pressure vessels.