Hydrostatic Testing of a fired boiler or PV

[NovaStark]

Good day all,

I am reviewing a hydrotesting procedure that my company has a standard for a specific fired boiler that produces medium pressure steam. So it has a firebox, steam drum,mud drum, economizer and superheater coils.

Now within the procedure is a graph showing incremental pressure steps and hold times e.g. 0 to 200 psi in 10 mins and hold for 5 mins and then up by another 200 psi in 10 mins and hold for 5 mins until the MAWP.

Now normally for this Operating pressure is < MAWP such that Op. Pressure is approximately 1.25*MAWP. I don't have the the BPVC Viii code on me but I think they suggest either 1.3 or 1.5 times MAWP.

For a unit with repairs, is going up to the MAWP endorsed by the code and does the code suggest pressurization rates and hold times per step or is there any documents explaining the logic behind pressuring up in steps apart from spotting leaks at a lower pressure (thus meaning you abort the pressure test)?

 

[TGS4]

ASME Section VIII, Division 1 is a Code for new construction. Therefore, it does not address repairs. Ask this question of your repair a Code.

For Section VIII-1, the test pressure is 1.3 * MAWP * Lowest Stress Ratio. That last quantity can greatly increase your test pressure for higher temperature designs.

 

[NovaStark]

I did see that formula in asme PCC-2 under " Hydrostatic Pressure Test of Pressure Vessels or Piping Systems". Based on that, would a hydrotest after a repair be unreliable if only tested up to MAWP and not 1.3*MAWP*Lowest Stress Ratio ?

 

[TGS4]

Pressure vessels and piping have different philosophies with regards to hydrostatic testing. Piping generally considers it to be a leak test, whereas pressure vessels definitely take credit for the beneficial effects (crack-tip blunting, favourable compressive residual tress fields, etc).

A test to MAWP only would be what I would consider to be a service test. However, if you have a higher LSR, then you aren't really doing a test that acknowledges that the material is fundamentally weaker at the design temperature, as compared to ambient conditions.

What are you trying to accomplish with a hydrostatic test after your repair?

 

[NovaStark]

Pressure vessels and piping have different philosophies with regards to hydrostatic testing. Piping generally considers it to be a leak test, whereas pressure vessels definitely take credit for the beneficial effects (crack-tip blunting, favourable compressive residual tress fields, etc).

A test to MAWP only would be what I would consider to be a service test. However, if you have a higher LSR, then you aren't really doing a test that acknowledges that the material is fundamentally weaker at the design temperature, as compared to ambient conditions.

What are you trying to accomplish with a hydrostatic test after your repair?

I believe after the repair, they're thinking that if they pressure test up to MAWP (with MAWP = 1.25 MAOP) and see that the pressure remains fairly constant within 30-60 mins, then they will be confident that the repair will hold out under operation. They'd be doing the test with water at around 120F whist under operation water is supplied at 266-300F and of course this being heated by a burner.

Also because they're using plant equipment to supply the water, I don't think our pumps can dead head to more than 20% above MAWP.