Hydrotesting of Old Boiler

The short answer is; it all depends. The boiler inspector is the person you should ask because the "code" is interpreted differently in different locals. Typically, he will de-rate the maximum allowable working pressure of an old pressure vessel depending on observed corrosion, age and other issues. That's the deciding factor for deriving the test pressure. It will always be higher than the RV set points.

Relief valves are gagged or blanked or removed during hydro. See your RV manufacturer for info on gags.

Dear Zippy2,

Thats a good comments. thanks anyway....

In general it is not good practice to rely on the pressure safety valve to save you if you exceed the design limits. PSVs can fail. And the design limit is 1.5 x, not the working pressure. And any pressure vessel fatigues with age; chemical attack and cyclic stress fatigue. How I teach my engineers to answer these '"Is it really necessary . . . " questions is one of Risk v. Reward. You save time, money, and trouble by skipping the test. Does your company take on huge risk if there is an incident? Summary: Are you comfortable explaining to the wife and kids of a colleague at his funeral how much time and money you saved by skipping a safety test? Then you have your answer. Set the safety bar high each day you walk in to work. Others will follow it. Those that criticise you . . . just repeat the above statement and do what is right!

Thanks for the comments. The safety valve will always be calibrated at least once a year for PPM as well as for safety reason. However, at normal boiler operation the operating pressure is less on the setting of safety valve as per code and standard. We always performed 1.5 x on hydrotesting after complete retubing of the boiler as standard procedure. Common explosion of direct fired boiler is cause by burner controller malfunction & unattended monitoring of Water level controls.

hi,

Your picture really brings smile on the faces in CR4

really? He might expect that to be notice at all. Is that your pic in reality? Then i may NOT keep looking while doing the hydrotesting of boiler. i will be careful next time or i might forget the pressure limit of my hydrotesting of boiler. Some guys will think that explosion may not avoided due to this sort of negligence.

My mother traded her pre-natal vitamins for Vodka and Cigars !

The National Board of Boiler and Pressure Vessel Inspectors directs in-service inspectors to pressure test a boiler to 1.5 times MAWP unless the boiler stamping has been lowered due to corrosion or design. This is to ensure that leak before burst criteria that was built into the vessel by the ASME code is still effective. Leak before burst allows an operator to shutdown safely (or run).

Even after a re-tubing, with the pressure elements replaced by an approved repair facility, a boiler may still retain its stamped MAWP rating after a hydrostatic test has been performed.

link to NBBI http://www.nationalboard.org/NationalBoard/CommissionedInspectors/InspectorGuides/CInsp_Guide_Firetubes.aspx

According to ASME BPVC, Section VIII, Division 1, latest edition, the hydrostatic test pressure, at ambient temp, P_h is :

P_h = 1.3 P (S_{all at amb. temp.} / S_{all at design temp.}),

Note : item (1.3 x Design pressure) not (1.5 x Operating pressure)

where, P = Design Pressure

S_{all. at amb. temp.} = Allowable tensile strength of vessel material at ambient temp.

S_{all. at design temp.}= Allowable tensile strength of vessel material at ambient temp.

For an old boiler, such rerating can be carried out to calculate the Max. Allowable Working Pressure , MAWP, depending on actual inspection reports.