Convection Tubes of Primary Reformer Furnace

[qaisarabbas]

We never inspected the convection tubes of our primary reformer furnace. These tubes are of different mater ranging from carbon steel to low alloy steel and manurite and containing process stream ranging from BFW to feed gas, fuel gas and saturated steam at elevated temperature & pressure.

I have heard that these tubes are usually leaked online specially at u bends due to erosion corrosion. But the problem is that we cant carry out UT of u bends due to small dia and sharp curvature. What would be the alternate methods for health assessment of convection tubes? Should be go for hydrotest? We are also thinking of replacing few sample tubes for destructive testing.

Please share your experience and advice.

Regards - Qaisar Abbas

[sakib321]

ya go for pressure test and for destructive testing why u not go for on site replica test to ensure the metallurgical structure integrity.
aside from this consult the furnace manual usually vendor provide the inspection plan for it
in our case we have it

[ben]

sakib321,
What does your inspection plan call for?

[sakib321]

it means the
extent of inspection required
time when need to inspect
method to inspect

[ben]

It would be nice if you share some info also under those heads.

[arcpro]

I have not seen any reference of hydrostatic testing of convection tubes in API 573 which covers inspection of fired boilers and heaters.
As per API 573 para (9)(b);
Destructive methods. One destructive method is removal of a tube or tube section deep in convection banks and inaccessible for direct measurement of the tube wall. However, with the availability of internal intelligent pigs to measure wall thickness, the need for destructive examination is lessened.
For pigs, I have seen FTIS (Furnace Tube Inspection System) which is applicable to both convection and radiant tubes. This system has been developed by QUEST. You may go to www.qi2.com for further details.

[qaisarabbas]

Thank you arcpro for suggesting pig inspection and confirming about destructive testing w.r.t. applicable api standard. What type of destructive tests should we go for?

sakib321, please share the details of inspection plan suggested by your vendor, as it is a common platform to share the knowledge.

Regards - Qaisar

[arcpro]

Metallographic examination can be performed for deterioration mechanisms, such as decarburization, carburization, hydrogen attack, and stress cracking. Physical testing of creep life can be appropriate for severe services and for affirming any calculated remaining life. Oftentimes, calculated remaining tube life include several assumptions of tube operating history that can lead to inaccurate results. The density of scale samples can be measured and may provide information on the tube operating history.
Any other destructive testing may also be performed which may provide some evidence on suspected damage.

You may consider checking your convection tubes with ECT, remote field testing for the accessible lengths.

[qaisarabbas]

Arcpro,

appreciating your response and elaboration. For our next plant turnaround, we will go for destructive tests (Metallography, tensile test, etc) of a sample tube & some NDT (UT, RT, Videoscopy) on other accessible tubes and their u bends.
Thank you for value addition.

[mechcolor]

1. UT of accessible tubes (without fins) to be taken especially on U-bends at both the ends of the reformer

2. Pig inspection has proven to be much effective but high cleanliness of tube ID is required plus a costly technique

3. Take out a sample from convection tubes (at least 24" long) both from finned and shock ones

4. Perform mechanical testing including tensile test which should come up with results of yield, ultimate strength, percentage elongation

5. Perform metallurgical testing of microstructure

6. Get creep analysis, results, changes in dimensions or microstructure

7. Metallurgical results must be taken at about 200 times magnification

8. Pressure test can be performed but against a well defined written procedure