Headquarters Office 1933 Dover Road,  Epsom, New Hampshire 03234 Phone:  603-736-4892           Fax: 603-763-3323   Engineering Office 150 High Street,  Canton, Massachusetts 02021-3611 Phone:  781-828-0451            Fax:  781-821-4091

March 19, 1998

Revised March 9, 2001

TO : Northstar Turbine Customers:

Subject : SULFIDATION

Gentlemen:

Frequently I am asked: What is Sulfidation? and, What can be done to prevent it?

What is sulfidation?

Sulfidation is a particular kind of corrosion which occurs to both nickel and cobalt based alloys. It is caused by sulfur which is found in ALL petroleum products including jet fuel. Since there is no such thing as sulfur FREE jet fuel, sulfidation is a persistent problem which requires our constant attention. Salt, air pollution, agricultural chemicals, and lead act as catalysts in the sulfidation reaction. As catalysts these four materials encourage the sulfidation reaction to progress more rapidly. Removal of these four catalysts, the use of protective coatings and metal alloys which are less susceptible to sulfidation are the only methods available to battle sulfidation.

What can be done to prevent it?

2.    The MORE Program, and the Pratt and Whitney Canada PT6A Maintenance Manuals, Section 71-00-00 describe turbine section wash.  This is the washing of the turbine section with clean water (i. e. drinking quality water.  It is necessary to remove one spark igniter and to insert a special wash nozzle into the engine to perform the turbine section wash.  PT6A engines with minor sulfidation problems should have turbine section wash once a week. PT6A engines with moderate or severe sulfidation problems should have turbine section wash once a day at the end of the day.  In cold weather it is necessary to mix alcohol with the water for this turbine section wash.  Since clean water is used for turbine section wash, it is almost impossible to damage the engine by washing it too often.

3.    The PT6A engine is allowed to use aviation gasoline (i. e. with lead) as an alternate fuel when Jet A, or an equivalent is un-available. Since lead is a catalyst for the sulfidation reaction, it is very desirable to plan flights so as to AVOID the necessity of using aviation gasoline at all. However, a true emergency is an emergency, and aviation gasoline may then be used.

4.    Everyone realizes that airports which are near salt water are a risk for salt exposure. Not everyone realizes that air ABOVE salt water up to an altitude of one mile (i. e. 1.61 kilometers) is also a risk for salt exposure. Bearing in mind that the pilot has to fly where he has to go, and where air traffic control tells him to go, any changes to the flight route which will minimize exposure to salt laden air will minimize the sulfidation problem.

5.    Air pollution, and agricultural chemicals are also catalysts for the sulfidation reaction. The comments about salt and salt laden air also apply to air pollution and agricultural chemicals, except that air pollution reaches much higher in the atmosphere than salt from the ocean does.

6.    Compressor turbine blades, and compressor turbine vane and vane rings are the engine parts most often attacked by sulfidation. In addition since these parts are very expensive to replace, sulfidation corrosion on these parts is to be avoided it possible. Pratt and Whitney Canada manufactures compressor turbine vane rings, compressor turbine vanes and compressor turbine blades with a pack process diffused aluminide coating on them. While pack process diffused aluminide is a fairly good coating, it is not the best coating to use to battle sulfidation. Sermaloy J is a silicon aluminide diffusion coating which can be applied to both cobalt and nickel alloys.  Sermaloy J has an thirteen year proven record of vastly superior sulfidation protection when compared with pack process diffused aluminide. There are several ways to obtain the benefits of Sermaloy J:

6A.    PWC turbine blade P/N 3102401-01 was introduced by PWC S/B 1346. It has pack process diffused aluminide and it will sulfidate. PWC turbine blade P/N 3039901 was introduced by PWC S/B 1455. It has Sermaloy J and is a significant improvement.

6B. Northstar Turbine is the manufacturer’s representative for Turbo Products, Federal Aviation Administration – Part Manufacturer Approval (i. e. FAA PMA) parts. Turbo Products turbine blade P/N T102401-100 is made from INCO 100 material and is Sermaloy J coated. It is as good as PWC P/N 3039901, and less expensive.

6C. Turbo Products turbines blades P/N T102401-01 and P/N T023401 are made from INCO 738 material and are Sermaloy J coated. The INCO 738 material is significantly more sulfidation resistant than INCO 100. The Sermaloy J coating is significantly more sulfidation resistant than the pack process diffused aluminide. The Sermaloy J coating and the INCO 738 work so well together that the improvement from using both of them together is dramatic. They are better than PWC P/N 3023401, 3102401-01, or 3039901, and less expensive.

6D. Turbo Products turbine blades P/N T102401-792 are made from INCO 792 material and are Sermaloy J coated. The INCO 792 material is significantly more sulfidation resistant than INCO 100. The Sermaloy J coating is significantly more sulfidation resistant than the pack process diffused aluminide. The Sermaloy J coating and the INCO 792 work so well together that the improvement from using both of them together is dramatic. They are better than PWC P/N 3102401-01 or 3039901. Un-fortunately Turbo Products P/N T102401-792 is expensive and may cost as much as the PWC turbine blades which it replaces.

6E. PWC turbine vane P/N 3019551 is made from WI52 (cobalt), it has pack process diffused aluminide and it will sulfidate. Turbo Products turbine vane P/N T019551 is made from INCO 738 material and is Sermaloy J coated. The INCO 738 material is significantly more sulfidation resistant than WI52. The Sermaloy J coating is significantly more sulfidation resistant than the pack process diffused aluminide. The Sermaloy J coating and the INCO 738 work so well together that the improvement from using both of them together is dramatic. It is better than PWC

P/N 3019551 and less expensive.

6F. PWC turbine vane ring P/N 3032651 is made from INCO 738, it has pack process diffused aluminide and it will sulfidate. Turbo Products turbine vane ring P/N T032651 is made from INCO 738 material and is Sermaloy J coated. The Sermaloy J coating is significantly more sulfidation resistant than the pack process diffused aluminide. The Sermaloy J coating and the INCO 738 work so well together that the improvement from using both of them together is dramatic. It is better than PWC P/N 3032651 and less expensive.

6G. Sermaloy J is such an improvement over PWC pack process diffused aluminide that some people have sent both new and used PWC turbine blades, vanes, and vane rings to overhaul shops to have the pack process diffused aluminde coating removed and Sermaloy J applied to obtain the additional sulfidation resistance. While having engine parts re-coated is a good option for some people, it makes better sense to buy the part with the correct coating in the first place.

6D. Turbo Products turbine blades P/N T102401-792 are made from INCO 792 material and are Sermaloy J coated. The INCO 792 material is significantly more sulfidation resistant than INCO 100. The Sermaloy J coating is significantly more sulfidation resistant than the pack process diffused aluminide. The Sermaloy J coating and the INCO 792 work so well together that the improvement from using both of them together is dramatic. They are better than PWC P/N 3102401-01 or 3039901. Un-fortunately Turbo Products P/N T102401-792 is expensive and may cost as much as the PWC turbine blades which it replaces.

6E. PWC turbine vane P/N 3019551 is made from WI52 (cobalt), it has pack process diffused aluminide and it will sulfidate. Turbo Products turbine vane P/N T019551 is made from INCO 738 material and is Sermaloy J coated. The INCO 738 material is significantly more sulfidation resistant than WI52. The Sermaloy J coating is significantly more sulfidation resistant than the pack process diffused aluminide. The Sermaloy J coating and the INCO 738 work so well together that the improvement from using both of them together is dramatic. It is better than PWC P/N 3019551 and less expensive.

6F. PWC turbine vane ring P/N 3032651 is made from INCO 738, it has pack process diffused aluminide and it will sulfidate. Turbo Products turbine vane ring P/N T032651 is made from INCO 738 material and is Sermaloy J coated. The Sermaloy J coating is significantly more sulfidation resistant than the pack process diffused aluminide. The Sermaloy J coating and the INCO 738 work so well together that the improvement from using both of them together is dramatic. It is better than PWC P/N 3032651 and less expensive.

6G. Sermaloy J is such an improvement over PWC pack process diffused aluminide that some people have sent both new and used PWC turbine blades, vanes, and vane rings to overhaul shops to have the pack process diffused aluminde coating removed and Sermaloy J applied to obtain the additional sulfidation resistance. While having engine parts re-coated is a good option for some people, it makes better sense to buy the part with the correct coating in the first place.

CONCLUSION – Sulfidation is corrosion, and corrosion is very persistent. It may be necessary to use a combination of the above listed methods to reduce sulfidation damage in moderate and severe cases.

Comments, Ralph Hawkins is the Chief Engineer for: MORE Company, Northstar Turbine and Hawkins Aero Engineering. If you need additional information call me at 781 828 0451, or

FAX me at 781 821 4091.

Sincerely,

Ralph Hawkins

Chief Engineer

Northstar Turbine LLC

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