We have an equipment under sour service with design conditions corresponding to 600# class rating. Max/ min Design Temp are 80/ -29 deg C.

Approximate shell thickness required with SA 516 Gr 70 is 100 mm. Fro the MOC, choice is in between SA 738 and Sa 516/ SA 515, I have few queries on selection of material;

1. What is the benefit of selecting SA 738 other than having slightly lesser thickness as compare to SA 516/ 516.

2. SA 515 is for intermediate and higher temp service so propabley not a preferred one for the given temperature.

3. SA 738 Gr A or C can be used (Gr B thickness is limited to 65 mm) but only Gr A is heat treated as per the code, What benefit we get for using Gr A or with Gr C?

4. Whether required impact properties can be achieved with SA 738 for the required thickness?

5. Code supplimentary requirement ask for impact testing at -50 deg F. My copy of the code gives 45 deg C value corresponding to -50 deg F, whether i am missing any thing , which figure is correct?

Request your advise.

Regards

Sanjeev

sanjeev_shukla70,

1. The benefit of selecting SA738 is the usual one for selecting steel grades with higher yield/tensile values. But there are certainly also drawbacks. I would not recommend such a high strength steel like SA738 (any grade) for sour service applications.

2. SA515 is a coarse grain steel and inappropriate for service temperatures of -29 deg C.

3. SA738 Gr.B is limited to 100mm according the actual edition. What do you mean by heat treated as per code? Grade A can be delivered in normalised condition up to 65mm, all other grades and thicknesses have to be quenched and tempered

4. Impact properties at -29 Gr.C can be achieved on all Grades of SA738 up to 100mm.

5. Where do you find a supplementary requirement with impact testing at -50 Gr F?

Regards

Hocke,

Thanks for your reply.

I think I was using an obsolete version ( of the code which was indicating a limit of 65 mm for Gr B and impact values in the supplimentary requirements appendix.

SA 738 referes back to SA 20 for general requirements however SA 20 table A 1.15 does not include SA 738 for impact test requirements. Any advise on impact test temperature and the values for this material.

Regards
Sanjeev

Sanjeev
SA738 contains an Appendix X1 with nonmandatory Information. There, longitudinal values of 20 ftlbs at -50°F in longitudinal direction resp. -20°F in transverse direction are shown. I assume, that the metric values for temperature given are erroneous and -45°C resp. -30°F should be correct.
Please note that these values have to be agreed with the material manufacturer.
Higher values or lower temperatures can probably also be achieved. But a general assessment is quite difficult, as minimum achievable temperature are strongly dependent of the chosen Grade, material thickness, PWHT conditions,.....
Moreover, SA738 is not among the most used steel grades in practice and probably not easy to find on the market.

Hocke,

Yes this is not a commonly used steel and we are already struggling to locate this grade. This is specified by the Client and we are trying to take a deviation tyo this.

Impact values and temperature are indicated in the appendix but -50 Deg F (45 Deg C) and -20 Deg F (30 Deg C) for long and trasnverse respectively.

Not sure which value of the temperature is correct.

In my copy metric values are positive ie 45 Deg and 30 Deg, where do you get -45 Deg C?

Sanjeev

Sanjeev
I assume that the metric values are simply misprints.
1) -45°C and -30°C are the commonly used metric values for -50°F and -20°F in ASME.
2) ASME generally considers minimum available temperatures in transverse direction higher than for longitudinal direction, see ASME SA20 Table A1.15. With +45°C in long and +30°C in transverse, this would be the direct opposite.
3) No one needs impact values at +45°C or +30°C for a steel grade declared for moderate or lower service temperatures.
4) As it is only an option in the standard, it is up to you to agree with the manufacturer the desired impact requirements. In my opinion, the construction code requirements (e.g. ASME VIII,1 or 2) regarding MDMT and minimum Charpy values should mainly determine the requirements and not the available options in a material standard. I understand the available values as a guideline for material selection. But you can not assume, that on material bought without impact requirements, you will always obtain these available values.

Regards