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As part of tank bottom plate replacement we are planning to make opening in the shell (42mm thick A537 CL2 material )in order to transport the plate inside the tank for bottom replacement.Is it mandatory to carry out PWHT for the shell opening weld joint as per the code?

regards,

What's the design code for tank? API 620 or 650?

1. The tank material A537 Class 2 is quenched an tempered falling in Group VI as per API 650.
2. Stress relieving is mandatory no matter whatever type of connection you make as the tank in question must be stress relieved.
3. Stress relief must be done on the pre-fabricated part (either you go for a monhole or a butt insert plate) before installation of the reinforcement plate (in case of opening for manhole).
4. The stress relieving temperature for the said material must be less than the tempering temperature.
5. Test specimens are also mandatory as per para 3.7.4.6 of API 650.

The above inputs were as per API 650 where there is a limitation to the thickness of 12.5 mm (for group VI material) at the welded attachment or nozzle opening. API 650 mentions about the connection whether it is flush type clean out fittings or flush type shell connection, stress relieving is to be done.

Now as per API 620, tank sections that have a nominal thickness of wall plate greater than 11/4 in.32 at any nozzle or other welded attachment and nozzle necks whose thickness at any welded joint therein exceeds (D + 50)/120 shall be thermally stress relieved after welding.

What are your plans for the opening after bottom plate replacement? Would you provide a manhole here? What's the size of the opening?
Any alteration must comply with API 653 requirements. Share your plans and then I may provide you some inputs.

Replace the whole shell plate where you provided the opening as per API 653 and for the shell API 650 does not lay down any PWHT / stress relieving requirements.
It's the best way to go.

Note: Local stress relieving is not permitted by API 650. Reinstating with a new shell plate as mentioned by mechcolor seems to be the right solution.

Thanks to all for the feedback. We want to make a elliptical opening in the first shell course for inserting the bottom plates and re-weld the old cut shell plate at the removed section(similar to insert plate)and do 100% radiography. Is it required to carry out PWHT for the shell weld joint? It is a old tank designed as per 650 and the above opening is required as part of tank refurbishment to replace the tank bottom plate.Repair will be carried out as per 653.

regards,

API 650 does not mention anything regarding PWHT of shell joints. If you just have to insert a plate just go for it without stress relieving as you cannot do anything with these welds. Any local PWHT is prohibited in API 650.

Refer to my last post, I would recommend replacing a shell plate where the opening was provided. Insert plate for the opening may or may not be manufactured in the way it should be whereas rolling a new plate as per tank diameter is a relatively easy and common practice of mechanical contractors.
During welding either for insert plate or shell plate, use proper pre-heat temperature, interpass and slow cooling after welding operation. No PWHT / stress relief required as per code.