ASME Intent

[jimishad]

Morning all,

We operate large HRSG's and have maintained them to 'ASME intent' for a number of years. Although you would expect this type of information to be readily available, it's not. The question is; does anyone else use an interpretation of the ASME codes to maintain their HRSG's.

Any information or guidance would be most appreciated.

Regards

Jim

 

[metengr]

jimishad;
We have several HRSG's and we follow OEM guidelines for operation and maintenance activities. In-service inspections and repair fall under the National Board Inspection Code requirements. I am not sure what "ASME intent" is that you are referring to because ASME B&PV code is a construction code, NOT an in-service code.

If it is in reference to ASME B&PV Code Sections VI or VII these are good sources for additional information on operation/maintenance of heating and Power boilers. We have used information from these sources to develop our own specific procedures for operating and maintenance of HRSG's to supplement OEM guidelines. However, we are not bound by nor required to follow ASME B&PV Code Section VI or Section VII.

 

[Sharik]

We would agree with metengr, our HRSG units are repaired/altered to the applicable Code of Construction (ASME Section i). This is a requirement in our Quality Control Program and in our Contractors' QC Programs.

Inspections are completed to the National Board.

 

[davefitz]

meteng is correct, the codes are design codes and not operating codes, but there are some areas where some areas of concern exist in the operationsof combined cycle plants.

2 areas that come to mind would be covered by B31.1 in the design , but apparently something seems to get lost in the translation.

B31.1 par 102.2.4 allows short term operation above ASME allowable stresses , but usually the time limits defined by ASME are not programmed into the DCS and there is then no time limit imposed on operators for such overpressure. Typically the worst case is overheat of the cold reheat pipe during startup windage heating of the HP turbine- normally this pipe is carbon steel and siche B31.1 does not provide allowable stresses for carbon steel above 750-800f, any overheat above 800 F is technically not permitted. A bigger concern is leakage past the HP bypass which may heat the carbon steel pipe above 800F for prolonged periods- this can lead to graphitization of this pipe.

Another area that sometimes does not seem to meet B31.1 rules is overpressure protection of natural gas lines. If 100% full casualty flow overpresure protection is not provided by relief valves, then B31.1 allows alternate overpressure protection provided several redundant mechanisms are in place , including:
a) 2 independent PRV's in series, both set to limit downstream pressure to bleow design pressure. Independent technially implies independent power supply and control systems- this is sometimes not met
b)downstream pressure switch, hardwired to an inlet stop valve. This inlet stop valve must have an actuator sized to close within 1 second.
c) other items- see the code

 

[jimishad]

Thanks for all the replies so far.

The main driver for the question relates to ASME IIIV particularly when repairing LP sections of the HRSG. I am led to believe we moved away from ASME as the PWHT timescales were excessive, and agreed an 'ASME intent' with our insurers. I have found some documentation relating to this and am reviewing; the question now is can you work to outside the ASME codes for repair and inspection?

Regards

Jim

 

[metengr]

Jim;
Most Jurisdictions in the US reference and require the National Board Inspection Code (NBIC) publication NB-23 for Inspection, Repair and Alteration activities of boilers and pressure vessels. The NBIC references the orignal code of construction in "so far as practical" to be used in performing repairs/alterations. As far as inspections, the NBIC has all of the necessary information related to this activity - ASME B&PV should not be used.

To answer your question regarding repair, yes, you can use other options for weld repair that are listed in the NBIC. For example, NBIC Part RD contains various alternative weld repair methods that are not mentioned in the ASME B&PV codes because you are dealing with an in-service pressure retaining item. In some cases, the orignal code may have required PWHT. However, this can become impractical or even result in damage to the component in certain field installations, that is why we developed alternative welding methods in the NBIC.

I would suggest you purchase a copy of the 2001 NBIC with the 2003 Addendum. Even though I sit on the NBIC main committee this is not a commerical plug, nor do my comments reflect those of the main committee.

 

[GenB]

I know that the ASME I is working on "tighten the belt" on HRSG's mfrs. because of the current problems.
You may call it intent. This will be for new construction only. They may address/pinpoint current problems and recommendations for maintenance of inservice of these.
For now the BNIC takes precedence over repairs in conjunction with the jurisdictions if in The US or Canada.
ER

 

[GenB]

There are some ASME bulletins addressing the problems and recomending repair procedures as well.
Ussually comes as topics on newsletters.
ER