NDT for ammonia storage tank

[purnawan]

Hi Dear, as per Code, whether phased arrays test method could be used for ammonia storage tank to replace radiographic test? What are the things that must be considered to make phased arrays test. Many Thanks

 

[Duwe6]

Mostly, the metal surface within 10cm of the weld have to be smooth to the touch, to allow the transducer to scan smoothly along. Also, since PA is not limited by the film cassette size, consider scanning more length than the API minimum at each test spot.

 

[weldstan]

ASME VIII, Div.1 permits the use of phased array testing as an alternate to RT. I believe that Code Case 2235-9 is stiil applicable, if so, obtain and review. Also, if s,o the minimum thickness of shell is 1/2". Most of the 2235-9 requirements have been incorporated into ASME V, Article 4.

 

[purnawan]

thanks gentlemen, in my consideration is the technical design of the ammonia storage tank follows API 620, while the phased array method has not been accommodated in API 620 (please correct me if I wrong). Therefore, technically, can I use PA method to replace RT method?

 

[Duwe6]

API 620, just like 650/653, allows the designated Inspector a lot of leeway. If your tank Inspector concurrs [in writing], then it is permissible IMHO.

 

[weldstan]

API 620 does have requirements for UT (Phased Array and TOFD)per Annex U.

 

[MJCronin]

purna.....

What type of ammonia is being stored in this tank ?

Does the tank store the more potent anhydrous ammonia or simply aqueous ammonia ?

In the USA, anhydrous ammonia is typically stored in ASME VIII pressure vessels, designed for 250 psig MAWP.

Anhydrous ammonia corrosion has caused vessel failure in the past

Additional vessel design/quality requirements is mandated by many US states and defined in ANSI K61.1

Aqueous ammonia is stored at a lower pressure.

Some information here:

https://www.osha.gov/dts/shib/shib120505.html

MJCronin
Sr. Process Engineer

 

[Duwe6]

Sounds like this is one of the huge semi-cryo low-pressure tanks; API 620. Typically a tank-in-a-tank, 50-100 feet in diameter with a 2-3 foot annular space filled with vermeculite for insulation, cooled to just below its boiling point. Is this guess correct, purnawan?

 

[weldstan]

Adding to MJCronin, vessels in anhydrous ammonia service and constructed from carbon steel must be post weld heat treated per UCS-56.

 

[purnawan]

many thanks weldstan, Duwe6, MJCronin to your advise and valueable information. Ammonia stored is anhydrous at temperature -33C. The tank is double wall, diameter of inner shell 40250 mm and outer shell 41750 mm. Annular space filled with perlite insulation. We have existing 4 ammonia tanks and we use RT for the inspection. How much that already applies the use of UT (PA) in lieu of RT on the ammonia tank.

 

[lganga]

purnawan

We have to erect an API 620 R double wall ammonia tank .
We are now reviewing the NDT inspection, to avoid future problems related to SCC
If you consider the figure R-2 we add all the verticals 100%RT+20% in the horizontal buttwelds.
If the tank has E=1 for the shell thickness calculation. Are these NDT tests covering the joint efficiencie E=1?.

We are thinkng in UT as alternative for RT .
Regards
Luis
See my thread in Storage Tank engineering

 

[IFRs]

Given the hazards involved, I hope you are considering going to a more rigorous test rather than a less expensive one.