Blind Flange on Pressure - Class Inspection requirements

[babman]

Hi,

This post is in relation to my first post about blind flanges a few weeks ago.

Essentially we have redesigned the upper head on a vertical process vessel to include a 8" handhole/inspection/removal hatch to remove a internal demister pad which has caused issue on several other projects.
The vessel is located on a compact skid unit located on a large ship.

In our design, we have moved over a 2" nozzle on the same head to accommodate the new 8" RFWN flange with counter blind flange - all to ASME B16.5 dims for a 300# rating.
This was decided as the best option, instead of having the 2" nozzle penetrate the blind flange and having to remove the connecting 2" spool pipe to gain access to handhole hatch.

Now one of our senior warranty engineers has dropped a potential grenade in saying that by now having this inspection hatch not connected to pipework, everytime we remove the blind flange and put it back on, we shall require class approval for stating the vessel is still fit for service at the design pressure.
We have a similar sized vessel on another area of the skid unit, where we utilise a 8" nozzle connection to gain access to demister pad - however the nozzle is directly connected to the inlet pipework.
The senior warranty engineer has stated that because it is connected to pipework, we can take it off as many times as we want and reinstate it without having class involved.

Some my colleagues involved in this project, including myself, are sceptical about his reasoning - can anyone shed any light or opinion on the topic?

Regards

 

[TGS4]

This phrase that you used here

class approval for stating the vessel is still fit for service at the design pressure

is something that is not familiar to me. Although you have stated that this equipment is located "on a ship", it would be helpful if you explained your jurisdictional requirements a little better.

 

[babman]

Hi TGS4,

Sorry if I haven't provided enough info for someone to follow on my query - I tend to write essays when only a paragraph is required, so I tried to keep my question as brief as I could.

The vessel details are:-

- classic cylindrical pressure vessel, vertically mounted with 2:1 elliptical heads.
- Situated on a modular compressor skid unit - comprising of various other PV's, 3 stage compressor, electric motor etc.
- Skid unit is situated in a compressor room on a large liquefied gas vessel - hence when I refer to class, I mean everything we order/design has to be maritime class approved i.e. Lloyds Register, ABS, DNV-GL

We design the vessel to whatever maritime classification society the ship is under - but also use ASME for checking flanges, nozzles, vessel wall thickness details.

I was just seeking any info on if there was any ASME or any class rule that stipulated that an inspection hatch/blind flange - not connected to any associated pipework with the pressure vessel - would require re-approval from a classification society or 3rd party inspector, everytime the blind flange was removed for inspection. That is what my colleague in the Warranty department has implied is the rule - however many others in my company as well as myself, are sceptical that this is the case.

I am drawing a blank from searching through the codes as well as the trusty mass Google searching.
An obvious question would be "Why are you not seeking further info from said Warranty engineer on this topic since they raised the question?", which would be the quickest route.
However said engineer has simply stated this scenario is the rule, it is up to us to prove to him that it is not the case.

Thus I was hoping that someone on this site, may have heard such a similar rule or could hopefully debunk my colleague's assumption - or at the least point me in the right direction.

Regards

 

[LittleInch]

He might state "this is the rule", but you need to question him further on which section, paragraph etc this "rule" has come from.

Given the same word "vessel" is potentially used for two completely different situations, i.e. vessel as in ship and vessel as in pressure vessel you might be referring to two different scenarios.

I can see that if you remove a blank flange which is intended to be a water tight element in the hull or bulkhead then it might need to be somehow class approval, but in the world of pressure vessels I've never heard of it before.

However ships and offshore systems like this are a world of their own and sometimes don't make sense to us land lubbers.

As said it is simply not acceptable for him to just state "this is the rule", without giving any documentary evidence. This needs to be challenged and the context of this statement understood within the mysterious rules of marine class approval. when you get it (if it exists) then come back to us.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.