Local Hydro, Hot Tap Nozzle Questions

[PipingEquipment]

There are several vessels in service that require new nozzles. The question has been asked can we do a full pen weld through the nozzle wall and not cut into the shell until later when a hot tap will be done on them. They want to hydro the nozzles against the shell before it is cut with the hot tap, but that hydro plan doesn't seem to me to account for all the stresses (because it doesn't factor in the shell that will be stressed out to the limit of reinforcement and because the shell is likely in a heat affected zone from the weld), can anyone comment on this approach, does it meet all Codes? Also I'm not sure that even doing a hot tap AFTER hydro is ok, wouldn't the tap change the metallurgy from heat and its piercing the shell...that seems a bit off too, but I'm told that it is an industry standard practice, has anyone seen this practice and does it meet the Code?

The original Code is ASME Section VIII div 1, and the repair code is NBIC.

 

[wsu1975]

PipingEquipment:
Pressure testing the nozzle to be hot tapped is indeed an industry standard practice (It was 10 years ago when I did the last one!). Remember that the nozzle AND the hot tap machine need to withstand the process pressure and temperature, hence the pressure test before the vessel is cut. The hot tap design and fabrication must meet the code of record or a NBIC authorized substitute, as well as, depending on the jurisdiction, the approval of the inspection and regulatory agencies. I recommend looking at the API Recommended Practice API RP-2201 “Safe Hot Tapping Practices in the Petroleum & Petrochemical Industries” and API 510, “Pressure Vessel Inspection Code” for guidance on what is required/recommended for hot tapping both piping and pressure vessels. There are materials that may not be compatible with hot tapping – that’s where the vessel engineer, welding engineer and materials engineer are needed for input. If you are working for a major oil company, or providing services to, there may be a standardized method (Sometimes proprietary) to perform hot tap design, analysis, installation, and testing. Ask to see if this is the case to ease your concerns.
I hope this helps!
WSU1975

 

[saplanti]

I agree with wsu1975. The catalog hot tap equipment in most cases do not reach the pressure equipment/vessel/pipeline operating pressure. So there is a need for reducing the operating pressure to the acceptable level for the application. Therefore you need to discuss the requirements with the hot tap equipment supplier to understand the restrictions, and compromise if you do not have an established method/procedure for the hot tap application. It seems you do not have one.

 

[PipingEquipment]

Ok thank you for addressing my concerns about the hot tap (something we would sub out).
So if this is industry standard then that means the metheod of hydro they propose is ok too? If so how is that ok with ASME Code, as the hydro doesn't pressure all pressure parts being modified (the nozzle and the shell), since there is no pressure on the inside of the shell and pipe at the same time. I thought the weld cap method on the back of the shell on a partial hydro was done that way so that the entire joint (nozzle to shell) is tested, but if the above method is ok then it would almost always be easier/cheaper to do then having to weld the cap in...can anyone set me straight here?

 

[jte]

Hi PipingEquipment-

There is some confusion in this thread due to the various definitions people use for "hydrotest". This term has various meanings as defined in ASME PCC-2 Article 5.1 and while you are asking about one meaning you are getting responses using another meaning.

First, ASME VIII Div. 1 does not apply since this is post-construction. Thus, while VIII-1 does not allow local hydrotesting (in this case a "pressure test" at 1.3 * MAWP adjusted for temperature) such as what you are describing or even using an internal "hydrotest cap", post-construction codes by their nature must be a bit more flexible. Thus, NBIC does not prohibit the use of hydrotest caps and an AI might even accept the "weld the nozzle to the shell and hydrotest it before cutting the hole" approach as a Code hydrotest.

As you note in your original post, the statics with either a hydrotest cap or the "before you cut the hole" method are all wrong and in my opinion such a test is useless in terms of assuring gross structural integrity.

In a nutshell, and working purely from memory and my own thoughts and experience, the current draft of a new article for hot tapping which is expected to be published in the 2018 edition of ASME PCC-2 will suggest that:

[ul]weld the nozzle on
do some NDE
attach the valve and hot tap machine
tightness test to the operating pressure (not MAWP) in order to ensure that the seals etc. are sound
perform the cut, close the valve, remove machine, etc.[/ul]

I'm a bit surprised with the comment that most hydrotest machines cannot handle "common" pressures... In my experience I do not recall running in to a pressure limitation on the basis of the machine itself, but certainly some folks are in industries with higher commonly seen pressures.

 

[saplanti]

jte,

You call "I'm a bit surprised with the comment that most hydrotest machines cannot handle "common" pressures... In my experience I do not recall running in to a pressure limitation on the basis of the machine itself, but certainly some folks are in industries with higher commonly seen pressures. ". I was not mentioning the hydrotest machines. I did focus on the hot tap operation itself only. I trust this eliminates the confusion.

 

[jte]

saplanti-

My comment was in relation to the hot tap machine itself, not a hydrotest pump. Perhaps our experiences are different in that I've never been directly responsible for obtaining a proper hot tap machine, I've always been the client's engineer and worked with well established companies which offer hot tapping services. It is these companies which provided machines with adequate pressure capacity so if they had to get a "special" machine it was done internal to their company.

 

[saplanti]

jte,

I do not criticize your experience and your posts here. You are probably right writing all these. However I also experienced that the supplier of the hot tap equipment asked for reduction in the operation pressure during the hot taping, not after. I guess this is the one you misunderstood my posts. I do not want to go further since the original poster did not mention anything about the operation pressures of the vessels and the selected equipment for tapping for us to get into the details. Our discussion is only on the possibilities. Regards.

 

[jte]

saplanti-

I think I understand. Good discussion.