Whether Sight Glass Should be Assembled with Vessel while performing Hydrotest ??...... Answer : NO

[shm8324]

thread794-329895


Dear All,

One interesting question raised on static equipment group (Facebook)…

Whether Sight Glass Should be Assembled with Vessel while performing Hydrotest ??
Person who has raised this query is handling one vessel with sight glass mounted over it. Its U stamp job, So AI insisted to assemble sight glass while performing hydrotest.
Different members of group also has such kind of experience so they mentioned Yes, it is required…

But after I did some study and search on code requirement related to such proprietary item, I found that ASME has excluded such proprietary item from its purview. So code rules cannot be applied to such proprietary item. I have answered it as follows.

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First I replied with some logic :
It's a glass.... brittle one... applying 1.3 x DP or MAWP.. would it not cause any problem during hydrotest ?? I think sight glass vendor might have checked its integrity but test pressure (pneumatic or hydro ) would not be that much high which we apply to pressure vessel. Also sight glass material spec not as per ASTM or ASME so we cannot insist that material integration to be checked as per ASME rules..
AI can accept U-2(g) i.e. any acceptable engineering method... if site glass manufacturer can furnish such test certificate or results it can be acceptable to AI...


After that I referred code ASME VIII-1 :

Paragraph U-1(e) defines the geometric scope of VIII-1. When constructing a pressure vessel to be code stamped, it is important to know where the Section VIII, Division 1, rules apply, and where beyond a certain boundary some other standard applies. The most common geometric scope definitions.
U-1(e)(4)—The first sealing surface for proprietary fittings or components. A common example would be a sight glass installed within a framed opening of the vessel.
Here first sealing surface is pad type flange joint with which sight glass attached with vessel. So beyond it attached sight glass is not falls under ASME purview.

ASME VIII-1 U-1(e)(4) clearly excludes proprietary devices like sight glass from ASME Purview.

Then some of ASME Interpretations concluded the same :

Interpretation: VIII-79-44
Subject: Section VIII, Division 1, U-1(e)(4)
Date Issued: July 12, 1979
File: BC79-345

Question: Under the provisions of U-1(e)(4), is a strain gage level indicator attached to a vessel beyond the first sealing surface exempted from the Scope of Section VIII, Division 1, or must it be considered a part of the containment, and be designed with material acceptable under Section VIII, Division 1?

Reply: Excluding relief devices, any gage or instrument attached to a vessel beyond the first sealing surface is excluded from the Scope of the Code and does not need to comply with Code requirements including Code acceptable material.

Interpretation: VIII-1-83-256R
Subject: Section VIII, Division 1, Non-metallic View Ports (This can be call as sight glass)
Date Issued: May 31, 1984
File: BC84-030

Question: Are non-metallic components attached to the first sealing surface of a vessel as referenced in U-1(e)(4) and AC-120(d) outside the scope of Section VIII, Divisions 1 and 2?

Reply: Yes.

If logic is sight glass going to be assembled as a part of vessel, then level gauge/ transmitter also going to be part of vessel. Such logic should also be applied to it and assemble it with vessel while performing hydrotest.... but that is not the case.... reason is simple. as it is proprietary accessories, its integrity lies with that manufacturer from whom this accessory is purchased so at the most we can ask accessories manufacturer to furnish such integrity test certificates so that same can be shown to AI in case they ask whether same is done or not.. For testing purpose pad type flange can be covered with obround blind and testing can be performed. sight glass integrity requirement needs to be asked to sight glass vendor to be confirmed as per applicable code or standard.

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If anybody have any different experience on it please share.

 

[metalonis]

We've done several Code vessels that included a sight glass. We've never hydro tested with the sight glass installed. The opening has always been plugged during the test. It's always been OK with our AI.

 

[TD2K]

When we've ordered pressure vessels, the instrumentation is all installed in the field so the vessel is never initially hydrotested with them in place.

I've seen some seal pots for pumps that have an integral level glass in the side of the vessel (Flowserve provides these). Those come from Flowerve with the gauges so I expect those are hydrotested with the gauges but that's an exception.

 

[ASMEQC]

We always hydro with the glass installed. The glass should always be rated higher then 1.3 of the MAWP and temp. Although we have had a few people install the wrong glass and it didnt work to well. To me the glass should be sealed before shipping and how do you know that it is without doing hydro with them. Just my 2 cents.

 

[moltenmetal]

If the gauge glass cannot withstand a hydro test, I do not want yo be anywhere near that vessel in service.

Hydro with the glass in place.

 

[shm8324]

If it is applicable to sight glass... Then same also needs to be asked for other auxiliary equipment like level gauge connections, float wells, and safety valves as they are also a part of equipment.

But that is not the case… as all these attachments are proprietary and do not follow any construction requirement (material, design, fabrication etc….) of ASME. We can ensure first sealing surface integrity by hydrotest (with applying 1.3 x Dp or MAWP hydro pressure as till that point all construction requirement of ASME is already satisfied).. but beyond that attached accessory do not follows the same…

Refer any obround type sight glass specification. It specifies Max. Operating Pressure and Temp. Same can be availed to AI in case they are raising question on integrity and pressure-temp. limit of sight glass..

So as per such specification we can select sight glass as per our equipment max. operating pressure or MAWP (not equipment hydrotest pressure because as per ASME it doesn't followed ASME construction requirement so no need to withstand such tremendous pressure test)…

At the most we can perform leak test of sight glass separately only to ensure there is no leakage causing cracks adhere on glass surface or any of its joint beyond first sealing surface… Please note that my view is not to exclude sight glass from any testing, but as per me UG-99 hydrotest pressure do not required to apply on this component… by any other method such integrity can be ensured….

I have replied based on what ASME is considering and reason behind it…. adding anything during bid stage doesn't proves that it should be a practice to be followed…. integrity can be ensured with other ways also… only hydrotest is not the only way to ensure… Also hydrotest will cause a brittle failure… and glass falls in such failure category, so it's always better to find other alternative for the same…

 

[moltenmetal]

A gauge attached by ASME flanges, like any other valve or instrument, may be removed for a test. But any gauge which has a custom fixture welded right into a shell or head is entirely another matter in my opinion.