Boiler Hydrostatic Testing

[txdilbert]

Guys,

Looking for some direction on this.

The organization I work for requires that boilers already in operation receive hydrostatic testing every year if steam or high temperature hot water. I have read conflicting information regarding the test pressure the boiler must be brought up to. Understand ASME has required 1-1/2 times the MAWP for the longest time, but is this only for boilers not yet put in operation? Is NBIC the prevailing standard in our case? NBIC does not appear to stipulate a minimum pressure for testing, only a maximum. What is typically done in the field?

Is the required test pressure higher for boilers receiving major repair or alteration?

thanks

 

[metengr]

mxengr23451;

First off, hydrostatic testing by definition applies to new construction (ASME Code) of Power boilers and is conducted at pressures between 1.3 to 1.5X MAWP. Once the boiler is placed into service, the NBIC should be the applicable code for boilers.

I see no reason to conduct annual hydrostatic testing. This practice is unncessary and can result in damage to your Power Boiler. Why? Hydrostatic testing is used to find gross leaks in boiler components during new construction, and is a practice that has been around for many years. The myth is that conducting a hydrstatic tests does not ensure safe operation for some period of time, it only means you have no through-wall leaks at the present moment.

Once the initial hydrostatic test is performed by ASME Code, you should not need to use repeated hydrostatic tests to find leaks. The NBIC provides use of pressure tests at lower pressure as a test method capable to find leaks, and will not result in harmful tensile membrane stresses in components that may have marginal tougness at ambient temperature. Remember, Section I components are not required to have a minimum notch toughness requirement because the components generally operate well above the nil ductility temperature in service.

So, what I would recommend is to rely on enhanced boiler inspection methods annually to verify the condition of your boiler, and use pressure testing (well below operating pressure - 25% of MAWP) and supplemtal nondestructive testing to verify the integrity of any leak repairs to your boiler. You want to preserve the life of your Power boiler and not damage it repeated hydrostatic tests.

 

[txdilbert]

metengr,

Thanks for your response.

NDT probably would not be very cost effective in our situation. If pressure testing is the route we want to pursue, do you think 25% of MAWP is adequate to verify leak integrity? This pressure would likely be similar to operating pressure. I would think we would want to do 80-90% of MAWP at a minimum. Do you disagree? I'd like your thoughts.

thanks

 

[metengr]

mxengr23451;
Here is the problem I have with pressure testing above 300 psig. The magnetite (oxide) layer that is protective on carbon and low alloy steel waterwall boiler tube ID surfaces can be fissured during pressure testing or hydrostatic testing using oxygentated water. As a result, tube failures from corrosion fatigue are probable.

This is why elevated pressure testing is not a good idea when it comes to in-service boilers. For our Power Boilers we use under 300 psi for pressure testing and in some cases I do a fill and static head to check for leaks. This meets the requirements of the NBIC and our Inspector understands what we are trying to accomplish by avoiding corrosion fatigue tube leaks in waterwall panels. Our tube failure rates from corrosion fatigue have dropped significantly since we have utilized this approach.

Again, the risk of brittle fracture of drums or headers using elevated pressure water at room temperature can be significant. This is probably the biggest threat I could see against hydrotesting in-service Power Boilers.

NDT can be very cost effective using borescopes, UT scans of waterwalls and basic visual inspections. If you need to use pressure testing as a crutch to find leaks, go with 300 psig or lower.

 

[rmw]

I guess the most "pins and needles" situations I have ever experienced in my professional life was pressure testing of in-service boilers and especially older boilers after some repair that required hydrotesting. I didn't worry about the repair, I knew it was good, I worried about what hadn't been repaired.

rmw

 

[BCbrad]

Your Authorized Inspector may also provide some guidance. In my past experience in-service boiler hydro tests have been permitted at 90% MAWP where the normal operating conditions are less than 90% MAWP. Also, there have been allowances to test 90% the relief valve setting.

Refernce NB-23 Part 2 Para. 4.3.1.2