Re: [PSUBS-MAILIST] ASME PVHO

In a message dated 11/1/2010 8:10:34 P.M. Central Daylight Time, ojaivalleybeefarm@dslextreme.com writes:

The other side of it is, how close, with the equipment available can you come to producing a cylinder that perfectly round. I remember Alex describing how he had quite difficult job getting his stiffeners pounded into his cylinder.

Brian

-----Original Message-----
From: owner-personal_submersibles@psubs.org [mailto:owner-personal_submersibles@psubs.org]On Behalf Of Sean T. Stevenson
Sent: Monday, November 01, 2010 5:57 PM
To: personal_submersibles@psubs.org
Subject: Re: Re: [PSUBS-MAILIST] ASME PVHO

A couple of years ago, I had a unit demonstrated in my office which was a direct 3D input device - it had a magnetic base, and a three-arm linkage terminating in a ball probe. The user simply touched the ball anywhere on the part to be measured, and touched a trigger button on the handle (or held it down) to capture the contact position. XYZ points (with respect to the base) were instantly entered into software. In the case of a cylinder, you would repeat this process until you had enough captured points to define the "cloud", then best-fit to a perfect cylinder to determine individual point deviations. The software spit out all of the statistics, outliers, etc. Impressive gear, but expensive, although I understand that you can rent this sort of stuff.

-Sean

On Nov 1, 2010, JimToddPsub@aol.com wrote:

Guys,

Considering a cylindrical hull sitting on a roller table for easy rotation:

My concept for measuring out-of roundness has been twofold:

(a) Construct a micrometer frame large enough to mount on a pair of stationary rails running fore and aft alongside the cylinder and measure the diameter at eight points (four pairs) around the circumference and at approximately every foot along the length. The critical part is to keep the two contact points (on opposite sides of the cylinder) for any given measurement exactly opposite fore and aft.

(b) To measure inside, use a spring-loaded micrometer such as I've used in the past to check the inside of a cylinder in an internal combustion engine. Same issue of exactly opposite pair points fore and aft.

It's been over 30 years since I've done either one. Is this methodology out of date? Is it too cumbersome? Are there now laser-based devices reasonably available for measuring the inside diameter at multiple points?

Would it make sense to just have an engineering service check the cylinder prior to doing any work on it and again after stiffeners and major penetrations have been welded in place rather than using the homemade procedures described about? I expect they would not use something as old fashioned as contact micrometers since industry commonly uses lasers to QC machined parts.

Thanks,

Jim

In a message dated 11/1/2010 3:48:08 P.M. Central Daylight Time, ojaivalleybeefarm@dslextreme.com writes:

Hi Hugh, I'm just saying you can only measure something with in the tolerance of your measuring device. I didn't know about the templates that you're talking about. How are you suppose to make those? Are they just a big round piece of metal? That would have to be measured before any obstructions were in the way. What do you do about a flat spot?

Brian

-----Original Message-----
From: owner-personal_submersibles@psubs.org [mailto:owner-personal_submersibles@psubs.org]On Behalf Of Hugh Fulton
Sent: Monday, November 01, 2010 11:26 AM
To: personal_submersibles@psubs.org
Subject: RE: [PSUBS-MAILIST] ASME PVHO

Brian,

I am not sure how to take that statement.

ABS rules has charts under section 5 for making templates for checking but these are in addition to the 1% tolerance on diameter measurements.

The templates appear to be very coarse and for localized deformation. Hugh

From: owner-personal_submersibles@psubs.org [mailto:owner-personal_submersibles@psubs.org] On Behalf Of Brian Cox
Sent: Tuesday, 2 November 2010 6:31 a.m.
To: personal_submersibles@psubs.org
Subject: RE: [PSUBS-MAILIST] ASME PVHO

Hi Hugh,

Seems to me your out of roundness is limited by your ability to measure it.

Brian

-----Original Message-----
From: owner-personal_submersibles@psubs.org [mailto:owner-personal_submersibles@psubs.org]On Behalf Of Hugh Fulton
Sent: Sunday, October 31, 2010 10:26 PM
To: personal_submersibles@psubs.org
Subject: RE: [PSUBS-MAILIST] ASME PVHO

Hi Jon,

I think that we should have the Q.A. part tied up for P-subs as well so that the home builders appreciate the requirement for roundness. I am afraid I am lacking in the understanding and math behind getting the answers and I think that Cliff, Sean, and you would come to some agreement as to a formula.

I cant believe that it is a misprint in ASME. I am missing something somewhere but I don’t know what. Chs, Hugh

From: owner-personal_submersibles@psubs.org [mailto:owner-personal_submersibles@psubs.org] On Behalf Of Jon Wallace
Sent: Monday, 1 November 2010 5:51 p.m.
To: personal_submersibles@psubs.org
Subject: Re: [PSUBS-MAILIST] ASME PVHO

Interesting catch, Hugh. Definitely something wrong with that formula.

On 10/31/2010 11:06 PM, Hugh Fulton wrote:

Hi Sean,

I am having problems with doing Q.A. on my shell for out of roundness. This is an area which is fairly important to measure.

I have applied the 1% rule as a general tolerance but trying to comply and understand the PVHO caclcs.

ASME PVHO-1-2007 has a section:-

1-7.13.3 (e) (2) Formula for c

c= 2.28(R/t)^0.54 cannot get under the required 2.8 with any normal measurements of a vessel .

Do you have any experience with this.

My diameter is 48” and the shell thickness 5/16” L is 15.75”

Have you done any calcs on this area.

Do/t for my purpose is 162 which falls within normal dimensions and under UG80.1 gives sensible answers.

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