Flame Spray

Yes infact it is an interesting area. To go in detail my mail was indication of the possible HVOF-High Velocity Oxy Fuel flame spray application method. With regard to your query, I would suggest you to have a look into http://www.finishing.com/ a technical forum which is dedicated for specialists in this coating & polishing industry including the ENP and other varieties of polishing. Aluminium is an expensive choice, and has high resistance to acidic and neutral environment / atmospheres. But is considered to of high risk in explosion due to Aluminium itself. And it is generally not a preferance for high temperature. I am aware of two monopolistic companies in the major valve market -Italy, one is flame spray, and the other is Praxair. If you are procuring your subject materials from this market, you can avail the service of these companies. Praxair in India, does not do this coating service to my knowledge. With regard to flamespray, the link below gives the basic list of coating nos. but it is a small list and you have to check with them for more information, they give these technical information only to thier regular customers on a limited info basis, as the detailed info of the individual coating material is not shared in the website and kept as an 'internal distribution copy'. It gives specific information on Application, mechanical, chemical, application procedure, hardness and life expectancy etc. being properiatary to them. But as a customer you can get this info for deciding on the exact coat you require for your application.
http://www.flamesprayusa.com/materials.php
http://www.twi.co.uk/j32k/protected/band_3/ksrdh001.html

With regards,
Kannan

"M K Malhotra" mk.malhotra@eil.co.in

Dear Kannan You have given a very elaborative and informative response. Many thanks for that. The last para is of interest to me in the manner that in one of our high temperature pipeline, we were considering to use Thermally Sprayed Aluminium as external corrosion coating to withstand high temperature. If you have further informatio on this subject please share.

Kind Regards.
Manoj K Malhotra Engg. Manager Pipelines, EIL New Delhi.

Just to highlight though known to many, B 16.5 spells as....

5.4.1 General. Ring joint gasket materials shall conform to ASME B16.20. Materials for other gaskets are described in Annex C. The user is responsible for selection of gasket materials which will withstand the expected bolt loading without injurious crushing, and which are suitable for the service conditions. Particular attention should be given to gasket selection if a system hydrostatic test approaches or exceeds the test pressure specified in para. 2.6. 6.4.5.2 Ring Joint. The side wall surface finish of the gasket groove shall not exceed 1.6 micro-m (63 micro-in.) roughness. (This finish is applicable for the gasket surface also.)

Secondly B16.20 lists .......

The hardness of few gasket material Soft iron is 90 BHN Low carbon steel is 120BHN F5 grade(4to6Cr-0.5Mo) is 130BHN SS410 is 170BHN SS304 is 160BHN SS316 is 160BHN SS321 is 160BHN SS347 is 160BHN

Thirdly .....

As the whole purpose of the hardness concern is not to crush the gasket or damage the damage the groove and to have the right leakage proofness. As any other joint, in these high rating class joints, I would recommend you to check the torquing requirement of these bolting in your project, which I suppose are having bolt dia >=2". Accordingly do the leakage check and consult the stress engineer to recommend the prefered hardness level of the gasket. The hardness difference is very important and linked to the torquing. Then choose your gasket material...again....suitable for the service though some may claim that the service will never be in contact with the gasket but it is not true in practical situation. For these reasons the B 16.5 leaves it to the design engineer.

Check this link for online bolt torque calculation
http://www.zerofast.com/torque.htm and http://tech.groups.yahoo.com/group/piping_valves/message/73

Irrespective of all these rules and approaches ...do qualify from your end if the contract is correct. Sometimes, does mistakes happen on either side(Contractor or Owner or PMC) That is why the big weapon called Concession request / Deviation request with different names.....is available, and....if you are sure of your method of qualification.

Finally......

Although it is recommended that the rings are to be of hardness lower than the flanges to assure tight joints when gaskets are replaced or renewed, this feature may not be possible to obtain in the case of various alloys. Stainless steel alloy flanges heat-treated for optimum corrosion resistance will have the same range of hardness as the ring gaskets of the same material annealed to minimum hardness. Setting hardness as a minimum does not mean to have any technical reasons except for gasket renewals. Nace materials are a different subject altogether. Pl. check it out. Also verify if this hardness is linked to specific gasket predefined by client/pmc. If so, do go for alternative gasket like soft iron as it is steam service in your case should not be a problem. Also check if the hardness issue, same incase of other flanges in the stream.

Else you have the alternative and expensive solution - Metal spray used for hardfacing of seats and balls of all type of valves. This technology came for the carbide coating in the glass industry. Technology came from LindeGas called 'Carboflam' was adopted by valve industry for the W-Carbide, Cr-carbide coatings which usually starts from 15 microns in thickness. The metal composition defines the temp resistance, corrosion, porosity,adhesiveness and the hardness, usually selected by the company which specialises in this kind of coating which are few in number and has become a highly controlled knowhow industry. However this is not the only technology available in the market.

http://www.linde-gas.com/international/web/lg/com/likelgcom30.nsf/repositorybyalias/glass_carboflam_new/$file/Carboflam_43491235.pdf

With regards,
Kannan.

desaid@toyoindia.com Sent by: piping_valves@yahoogroups.com
28/11/2007 04:49
Subject [piping_valves] Increase the Hardness of RTJ groove?

Dears, Can any one give suggestion / opinion on below situation. We have flanged valve having RTJ flanges as end connection. The requirement is to have the min. hardness of groove as 160 BHN. Vendor is offering quite less hardness than 160. (Valves already manufactured.) How can we increase this hardness?
By overlaying or cladding ?
Or by any special treatment?

Please help.

Thanks in advance,
Dhwani Desai.