Pressure test & API579-1 FFS

[JVT_Stress]

Hello,

A FFS service level-3 assessment of a corroded ASME B16.9 BW TEE needs to be performed for general metal loss.
The orginal piping code is ASME B31.1
The material of the piping system is A106Gr B with a design pressure of 50Barg and a design temperature of 410°C.

1st question : is a new pressure test always required after a FFS assessment?

Although the original design temperature is 410°C, based on conversations with the plant personnel a max peak temperature of 385°C has been observed (not continous)
Which is about 14°C above the creep limit of 371°C for A106GrB material.
Since the design code is ASME B31.1, creep has been taken into account in the original design.
A loading histogram is not available.

2nd question : Is creep a significant factor to be considered in the FFS assessment, based on the above measured data of 385°C peak temp for A106GrB material?

Best regards,

 

[BJI]

1. No, pressure testing is normally for repairs and alterations, not for FFS. Creep is influenced by sustained stress at temperature, peak fluctuations would be of lower consequence but might need to be considered for creep-fatigue interaction.

2. It could be if operating under creep conditions. For your situation it is unlikely to be significant but should be considered for the ongoing operation at reduced wall thickness.

 

[TGS4]

2. Your answer to this is contained inn Table 4.1 (Hint: yes, creep needs to be considered).

 

[ReliaEng2008]

Are you doing a FEA (level 3) on a CS tee? Why can't you just replace it? It looks like you can take it out of service, since you considered pressure testing it. I would not spend the time and money to do a level 3. Have you tried FFS levels 1 and 2 before requesting level 3?

Regarding creep: how come the design temperature is above the creep temperature for A106? I don't think that design would be approved.

Need more info

 

[JVT_Stress]

Hello,

Thank you for the replies. I have checked table 4.1 and creep starts already at 343°C for the material concerned.
I have requested a load history diagram from our client (pressure and temperature, number of shut downs and start ups, etc...) but this is not available.

API 579-1 FFS points in the direction of Omega testing protocol, to obtain material parameters and creep damage.

@ReliaEng2008,
Thank you for your post. Unfortunatly we are not the owner of this plant, so we cannot decide to replace this piping system by ourselfs.

The only way I see to justify the replacement is to perform a FFS calculation including metal loss and creep and estimate the remaining life.
API 579-1 FFS states clearly that components such as ASME B16.9 BW tee is to be assessed with a level 3 assessment. (I think this is because ASME B16.9 are proof tested not calculated, so i do not know the orginal wall thickness when the BW TEE was new)
This piping system is more then 20 years old, but was not in continious service (it only served for start up and shut down of an energy plant).
We need to advice our client correctly and replacement is also an option in my opinion, but our client wants a justification from our company first, before we start the replacement.
Relating to why the design temperature is above the creep temperature, because ASME B31.1 allows this. Benchmark for creep in ASME B31.1 is 100.000h.
Creep was taken into account in the original design by using the allowable stress at 410°C from Appendix A-1.
But this is not my concern, I was still at university obtaining my engineering degree at that time;-)

The question is how can i know if these 100.000h have already been reached, without a load history diagram?

 

[TGS4]

Without a load histogram, you will need to make some assumptions, and run those assumptions past your client.

Don't forget that those 100,000 hours are based on the design temperature, and your operating temperature is lower.

 

[GD2]

JVT Stress,
It seems you are talking two things here.
1. Assessment for general Metal Loss, and
2. Assessment for creep damage and determine Remailing Life.

Here is my advice:
1. Evaluate General Metal Loos by API 579 Part 4. You can do a Level 2 assessment for Type B Class 2 component (ASME B16.9 has no design equation but has a design procedure).
2. Evaluate for Creep Damage by API 579 Part 10. This is tough because don't have a past load histogram.
No worries, you can get way out of it, by using the MPC Project Omega Method.
MPC project Omega program had developed a testing protocol by taking testing sample from the location of the component to establish material parameters for determining remaining life.
In your situation, this may not be practicable. You can fairly estimate the remaining life from tested material properties under similar conditions from Tables given under part 10 of API 579.

There are two parameters used in the industry - Omega Parameter and Larson-Miller Parameter.

You need to use the Project Omega Method as there is no past operational history.

The 1000,000 hrs you stated is one of the many criteria Codes uses to determine the allowable stress for the component at the design phase.

After service, you need to apply a post-construction code like API 579 to evaluate the component for continued service.


GDD
Canada