Old ASME SEC VIII Div I application

[orama]

Could someone help me please: I need to perform one huge modification in a CS (SA 515 Gr.70) vessel, built under the old ASME SEC VIII Div I Ed. 1978. My question is:
Is it necessary to recheck this vessel under both old and current edition or it is necessary only to perform the calculation notes under the new edition? Should I use the old code streeses instead the new ones?
Thanks in advance.

 

[jte]

orama-

You can perform your calc's to the current edition of Div. 1 using the old allowable stresses for the old SA515-70 material.

For the new material you may have more options. I have designed alterations for old vessels where the alteration uses the new allowable stresses. This is something I cleared (in writing - well, email) with our jurisdiction first. Many would say that you have to be consistent within the vessel, so check with your AI and jurisdiction. A good example of an alteration that I did was replacing the corroded heads on a vessel. The replacements were identical, same material, thickness, dimensions. However, I was able to use the current allowable stresses for the material and thereby gain some corrosion allowance. Although the replacement was physically identical, since I used different allowable stresses it was considered an alteration. The main thing was to be clear on the Manufacturer's Partial Data Report and the R-1 about which stresses were used. The hydrotest pressure was based on a factor of 1.5, not 1.3, since the circumferential seams were attaching to the existing shell.

jt

 

[unclesyd]

jte,
Did your AI require a hydrotest at 1.5 or was this your decision?

 

[JoeTank]

Orma,
It is entirely acceptable to check the vessel per the origonal Code and design the mods per the original Code also.

Steve Braune
Tank Industry Consultants

http://www.tankindustry.com

 

[unclesyd]

SteveBraune,
What I was getting at is if you use the newer code for the head materials and there is known corrosion in a vessel why go back to the 1.5 x Hydro instead of the newer 1.3 x.
Even in saying this I realize that each case needs to be evaluated by a design engineer and/or a materials (corrosion) engineer then discussed with the jurisdictional authority prior to commencing work.

I just don't think it’s good practice to subject an operating vessel to any deliberate pressure excursions beyond the minimum required by the code.

 

[JoeTank]

unclesyd,
I was not disputing the good stuff you offered. It just looked like the orama was going to get wrapped around the axle with all of the what-if stuff that was coming in. I just wanted him to know that he could keep it simple by going back to the original Code and avoiding the re-rate/ alteration route. As always, yor comments are worthy of note.

Steve Braune
Tank Industry Consultants

http://www.tankindustry.com

 

[unclesyd]

SteveBraune,
No problem and I agree with you whole heartedly about getting wrapped up in a situation. This only means more meetings getting too many people involved.

 

[jte]

unclesyd, SteveBraune, and orama-

Yup, I could've been more clear that the entire job, new steel and old, can be designed and fabricated using the old allowable stresses for simplicity.

I made the decision to hydro to 1.5x instead of 1.3x for a few reasons: The corrosion was limited to the heads only (impingement issue)so I have confidence in the shell. It avoided a longer discussion with the jurisdiction. Clearly, the heads can take it (physically identical ones did some 30 years earlier). Here's one I wouldn't have thought of in my old life working for a major Engineering and Construction outfit: The HAZOP remote contingencies (e.g. power outage + steam outage at the same time which takes some critical pump and its backup out of commission) sometimes are evaluated based on allowing the vessel to see 1.5*MAWP (the "two thirds" rule commonly seen on exchangers is directly related). Changing this vessel to 1.3x on the hydro might have impacted the HAZOP. Before people get too excited about this, let me assure you that a "design contingency" is evaluated to keep the vessel below MAWP. This would be something like a single critical pump fails, or we have a power outage. This types of situation can be reasonably expected to happen during the life of the vessel. The "remote contingency" is something, usually two or more issues acting together, which is not likely to happen, but is considered in the HAZOP.

In essence, I saw no reason to be concerned about a 1.5x hydro and there were several advantages to it.

jt

 

[deanc]

The actual words are in the NBIC RC-1020,RC-3000,and Appendix4 under Original Code of Construction. These all point you in the direction outline in the previous posts.

 

[jay165]

jte:

Not to beat a dead horse, but wouldn't the relief valve prevent the vessel from seeing 1.5 the MAWP?

 

[jte]

jay165-

The relief valve capacity is set by the design contingency.

A remote contingency may result in higher loading. Say we loose a cooling circuit due to simultaneous power loss and steam system failure knocking out the all of the cooling water pumps. The liquid in the system may flash and overwhelm the relief valves which were designed for a lower relief need.

jt

 

[jay165]

Interesting approach. I'll try to use that at the next HAZOP. Thanks for the reply!