Re: Re-rating - pressure test thoughts

From: <Christopher>
Date: Sat Sep 10 2005 - 00:04:00 EDT

On Sep 9, 2005, at 11:57 AM, aluser2 wrote:

> chris, it is legit under the code.

I don't think so, but if you can cite me chapter and verse, I'll consider it.

First, the Code doesn't 'rate' anything. The pressure vessel codes are a set of rules to be followed in the construction of pressure vessels. If the AI finds that all the applicable rules are followed for the construction and service conditions, the vessel may be stamped with the ASME cloverleaf for a specific MAWP. The Code plate isn't a 'rating;' it simply indicates that the vessel construction accords with Code rules. Once the stamp is applied, construction ends and that's the end of the Code's purview. There is no 'rating,' just a statement of compliance. This is covered in the Foreword to Section VIII, and I suspect you'll find similar language in the piping codes. You can't convert a non-Code vessel into a Code vessel just by doing numbers or with a hydro-test, and you can't make a Code vessel stamped with a MAWP of 250 psi into a Code vessel stamped with a MAWP of 275 psi--once the stamp is applied the Code has no more to say.

Moreover, the code can't 'rate' a vessel because it makes no statement of suitability for a given service. The owner takes that responsibility when he installs the vessel. That's covered in the Foreword, too.

After installation, modifications are governed by the jurisdictional rules. If the jurisdiction is loose, the owner or his agent might 're-rate' or fiddle to his heart's content, up to the point where injury or property damage occurs and the insurors or the courts take over. But the ASME Code has nothing to do with it, because it only governs new construction. The National Board Inspection Code part RA may apply to modifications or repairs, again depending on the jurisdiction. But not the ASME Construction codes. If the jurisdiction is tight or OSHA rules apply, the owner who operates a Code-stamped vessel at a pressure higher than the MAWP may face fines or loss of insurance coverage

That said, I don't think any jurisdiction can prevent an owner from contacting someone to run numbers or do tests and make a judgment that a vessel can be used at some other pressure than that found on the Code plate. To that extent 're-rating' up or down is possible. But it is not in compliance with the Code because the Code only applies to new construction. And the parties involved necessarily assume all liability in the event that things don't work out, including civil penalties for violating any jurisdictional requirements mandating Code rules for pressure vessels. That's because the ASME Code represents the standard of care for pressure vessel design in the US and Canada. When you take liberties with the Code rules you're sticking your neck way out. If you're running a Code vessel stamped for a MAWP of 250 psi at a service requiring 300 psi, you're ignoring the standard of care, and if anything happens, you're on the hook for it--the Code won't save you.

Christopher Wright P.E. |"They couldn't hit an elephant at <a href="/group/PipingDesign/post?postID=CQq76tIpH3uJfg_VtR5Z-N-0LZoaS9UjXh-8ddOlDy5j0j13SKiHMzRr3nGehTA-XD2TXww_BjF6Ebs">chrisw@skypoint.com</a> | this distance" (last words of Gen.

.......................................| John Sedgwick, Spotsylvania

1864)
<a href="http://www.skypoint.com/~chrisw/">http://www.skypoint.com/~chrisw/</a> Received on Sat Sep 10 00:04:00 2005